Vol. 20 No. 4 (2010)

Nuclear Physics News International

Volume 20, Issue 4 October–December 2010

FEATURING: Laboratory Portrait: The ISOLDE Facility • Weak Decay of Hypernuclei • Charmonium Specroscopy — A Tool for Understanding the Strong Interaction Nuclear Physics News Volume 20/No. 4

Nuclear Physics News is published on behalf of the Nuclear Physics European Collaboration Committee (NuPECC), an Expert Committee of the European Science Foundation, with colleagues from Europe, America, and Asia.

Editor: Gabriele-Elisabeth Körner Editorial Board T. Bressani, Torino S. Nagamiya, Tsukuba R. F. Casten, Yale A. Shotter, Vancouver P.-H. Heenen, Brussels (Chairman) H. Ströher, Jülich J. Kvasil, Prague T. J. Symons, Berkeley D. MacGregor, Glasgow M. Toulemonde, Caen Editorial Office: Physikdepartment, E12, Technische Universitat München, 85748 Garching, Germany, Tel: +49 89 2891 2293, +49 172 89 15011, Fax: +49 89 2891 2298, E-mail: [email protected]

Correspondents Argentina: O. Civitaresse, La Plata; Australia: A. W. Thomas, Adelaide; Austria: H. Leeb, Vienna; Belgium: G. Neyens, Leuven; Brasil: M. Hussein, São Paulo; Bulgaria: D. Balabanski, Sofia; Canada: J.-M. Poutissou, TRIUMF; K, Sharma, Manitoba; C. Svensson, Guelph: China: W. Zhan, Lanzhou; Croatia: R. Caplar, Zagreb; Czech Republic: J. Kvasil, Prague; Slovak Republic: P. Povinec, Bratislava; Denmark: K. Riisager, Århus; Finland: M. Leino, Jyväskylä; France: G. De France, GANIL Caen; M. MacCormick, IPN Orsay; Germany: K. Langanke, GSI Darmstadt; U. Wiedner, Bochum; Greece: E. Mavromatis, Athens; Hungary: B. M. Nyakó, Debrecen; India: D. K. Avasthi, New Delhi; Israel: N. Auerbach, Tel Aviv; Italy: M. Ripani, Genova; L. Corradi, Legnaro; Japan: T. Motobayashi, RIKEN; Mexico: J. Hirsch, Mexico DF; Netherlands: G. Onderwater, KVI Groningen; T. Peitzmann, Utrecht; Norway: J. Vaagen, Bergen; Poland: B. Fornal, Cracow; Portugal: M. Fernanda Silva, Sacavém; Romania: V. Zamfir, Bucharest; Russia: Yu. Novikov, St. Petersburg; Serbia: S. Jokic, Belgrade; South Africa: S. Mullins, Cape Town; Spain: B. Rubio, Valencia; Sweden: J. Nyberg, Uppsala; Switzerland: K. Kirch, PSI Villigen; United Kingdom: P. Regan, Surrey; USA: D. Geesaman, Argonne; D. W. Higinbotham, Jefferson Lab; M. Thoenessen, Michigan State Univ.; H. G. Ritter, Lawrence Berkeley Laboratory; G. Miller, Seattle.

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Vol. 20, No. 4, 2010, Nuclear Physics News 1 Nuclear Physics Volume 20/No. 4 News

Contents Editorial...... 3 Laboratory Report The ISOLDE Facility by Alexander Herlert ...... 5 Feature Articles Weak Decay of Hypernuclei by Elena Botta and Stefania Bufalino...... 13 Charmonium Spectroscopy—A Tool for Understanding the Strong Interaction by Ulrich Wiedner...... 19 Facilities and Methods AGATA and GRETA: The Future of Gamma-Ray Spectroscopy by I-Yang Lee and John Simpson...... 23 The WASA Facility at COSY by Magnus Wolke...... 29 Meeting Reports 11th Symposium on Nuclei in the Cosmos (NIC XI) by Klaus Blaum, Norbert Christlieb, and Gabriel Martínez-Pinedo...... 33 The Second Edition of the State of the Art in Nuclear Cluster Physics Workshop by Christian Beck, Pierre Descouvemont, Marianne Dufour, and Jean-Marc Sparenberg ...... 34 First Azarquiel School of Astronomy by Inma Domínguez and Carlos Abia...... 36 News and views ...... 37 Obituary...... 38 News from EPS/NPB ...... 39 Calendar ...... 40

Cover illustration:

2 Nuclear Physics News, Vol. 20, No. 4, 2010 editorial

Jefferson Lab in Transition

It’s been said that when you are tion of the beams. The past year saw a component of the project. Physics through changing, you are through. series of parity violation experiments, apparatus are being assembled, and Fortunately, for the U.S. nuclear including the measurement of the many accelerator components are physics community, there are many neutron radius of lead; the second arriving. We are looking forward to a changes taking place. phase of measurements forming a first, six-month, installation shutdown For example, in a recent editorial, complete set of photoproduction of the accelerator in spring 2011. Bob Tribble, former Chair of NSAC, experiments on the proton, which During that shutdown, we will make described the state of nuclear physics should provide a model-independent the penetration into the existing accel- in the United States. Bob correctly determination of all the relevant erator stub to transport the beam line emphasized the success in develop- amplitudes; and the installation of the to the new Hall D. A year later, a ing a plan that the funding was Q-weak experiment, the most recent 12-month shutdown will allow the com- able to support. The primary compo- of the parity-violation experiments. pletion of the accelerator upgrades. nents of that plan—construction of These experiments and others mean Then, we will start to commission the the 12 GeV Upgrade to the Jefferson we have a full experimental program accelerator. Lab accelerator facility, CEBAF; scheduled through spring 2012 and, For some time, Jefferson Lab also launching of FRIB, a new rare iso- given the hard deadline for cut-off of has operated a very high-power, tope facility; a targeted program of the accelerator driven by the construc- infrared free-electron laser (FEL) sup- experiments to investigate neutrino tion of the upgrade, extensions of run- ported by funding from the Office of properties and fundamental symme- ning time are hard to come by, placing Naval Research. The FEL takes tries; and the support of upgrades for a premium on readiness. Despite this advantage both of SRF technology the experiments and the RHIC col- full program and a growing 12 GeV and the beam energy-recovery tech- lider at Brookhaven—are all in nuclear physics program, we have nique. Recently, a new beam line was progress. received several letters of intent and installed using Air Force funding, and A laboratory portrait of Jefferson proposals for searching for so-called we now are operating a free-electron Lab also appeared in the previous dark photons, which may be possible laser in the ultraviolet regime. With issue Nuclear Physics News. That harbingers of dark matter. This is a the higher harmonics of the ultraviolet article gave a fairly broad discussion new departure and, perhaps, an laser, this facility could support of the range of nuclear physics topics important extension of our physics experiments with photon energies of being explored at the laboratory and scope. 10 eV, significantly expanding the our plans for 12 GeV Upgrade phys- The 12 GeV Upgrade is a major physics reach and possibly pointing ics. It also touched on the existence of project for the laboratory; we have the way to a 100 eV laser in the a free-electron laser. The basis for the more than 120 full-time equivalent future. success in both of those fields is the people working on it. As one of the During the past few years, the excellence of our superconducting economic stimulus initiatives, Depart- DOE Office of Science has recog- radiofrequency technology (SRF). ment of Energy (DOE) funding for nized that a number of the national Here, I would like to discuss further the project was accelerated with laboratories are using buildings that the full range of changes that are tak- money that moved from 2010 and are 50 years old and more; this is the ing place at Jefferson Lab. 2011 into 2009. The major construc- case at Jefferson Lab. So we have Our nuclear physics program with tion of the new experimental hall, been approved for, and are already in the 6 GeV accelerator has evolved to Hall D, and the extension of central the construction phase of, a signifi- exploit more and more the high inten- helium liquefier buildings are just two cant extension of our test laboratory sity, stability, and excellent polariza- very visible elements of the civil space and the addition of two new

The views expressed here do not represent the views and policies of NuPECC except where explicitly identified.

Vol. 20, No. 4, 2010, Nuclear Physics News 3 editorial

buildings. These changes both expand tor systems in nuclear power our space for preparation of experi- generation. The major projects in the ments and enhance the processing laboratory also have been supple- facilities in the superconducting mented, again as part of the economic radiofrequency center. In turn, we stimulus funding, by significant gen- will then be able to participate in several plant project funding from the eral future accelerator projects across DOE Office of Nuclear Physics. the DOE’s Office of Science, such as The result is that Jefferson Lab is the FRIB project at Michigan State changing. Its physics programs are University, perhaps Project X at Fer- being regenerated, and the labora- milab, the power upgrade of the Spal- tory’s technical capabilities and phys- lation Neutron Source at Oak Ridge, ical appearance are all changing. This and the next-generation light source, is a major transformation, which in wherever it might be built. We can turn is generating a strong sense of also imagine that our accelerator rejuvenation and enthusiasm. We developments might lead to more have the basis to continue as a major HUGH MONTGOMERY direct societal impact through initia- center for nuclear physics during the Jefferson Lab tives such as accelerator driven reac- decades to come.

4 Nuclear Physics News, Vol. 20, No. 4, 2010 laboratory report

The ISOLDE Facility

Introduction the United Kingdom. Negotiations permanent experimental setups are the The ISOLDE facility [1–3] is one with other countries are ongoing. gamma detector array MINIBALL, the of the world-leading laboratories for mass spectrometer ISOLTRAP, the the production and investigation of ISOLDE Experiments laser spectroscopy setups COLLAPS 3 4 radioactive nuclei. ISOLDE belongs to In order to perform experiments at and CRIS, the He- He dilution refrig- CERN’s accelerator complex situated ISOLDE, proposals have to be submit- erator NICOLE, the weak interaction on the border between Switzerland and ted to CERN’s ISOLDE and Neutron experiment WITCH, and the total France (Figure 1). The facility has Time-of-Flight Experiments Commit- absorption gamma spectrometer TAS. been in operation since its start in 1967 tee (INTC). The INTC meets regularly A more detailed description of these and is presently receiving protons from to evaluate experiment proposals as experiments is given below. the Proton Synchrotron Booster (PSB) well as letters of intent, which aim at of CERN. The success of ISOLDE is new experimental techniques or the Physics at ISOLDE due to the continuous development of development of new beams. After rec- The experiments at ISOLDE focus new radioactive ion beams and ommendation by the INTC and mainly on modern nuclear structure improvement of the experimental con- approval by the CERN Research physics. In addition, front-line stud- ditions. With the upcoming high Board, experiments may request their ies in other fields are pursued. The energy and intensity upgrade HIE- allocated number of radioactive ion energy range of the investigated radi- ISOLDE the possibilities for experi- beam shifts for scheduling. In general, onuclides goes from 10–6 eV in the ments with exotic nuclei will be further ISOLDE experiments are scheduled case of low-temperature nuclear ori- boosted. This laboratory portrait gives within 1–2 years after approval. entation at NICOLE to 3 MeV per an overview of the present facility that Many experiments install their own nucleon in the case of post-accelerated will focus on the status of radioactive experimental equipment in the beams at REX-ISOLDE. ion beam production, the operation of ISOLDE experimental hall, although a The nuclear structure is reflected ISOLDE, and the main experimental large fraction of approved experi- in many ground state properties of equipment rather than aiming at a com- ments make use of permanently nuclei, for example nuclear masses, prehensive summary of physics results. installed setups or common equipment nuclear charge radii, spins, and already in place. In particular, for the moments. With the investigation of The ISOLDE Collaboration solid state physics community, collec- excited nuclear states the evolution The ISOLDE facility is run by tion points are available to accumulate and behavior of shell closures can be CERN staff, mainly from the engi- radioactive ions for further use in off- studied. Shape evolution and coexist- neering and beams departments, and line experiments. Among the more ence in many regions of the chart of is an integral part of the CERN accelerator complex. The ISOLDE user community is represented by the ISOLDE Collaboration, which has an important role in shaping the science program at ISOLDE and the technical developments around it. The ISOLDE Collaboration officially holds the Memorandum of Understanding with CERN that covers legal aspects. The member states of the collaboration are Belgium, CERN, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Figure 1. ISOLDE facility situated on the Meyrin site of CERN across the Norway, Romania, Spain, Sweden, and border line between Switzerland and France.

Vol. 20, No. 4, 2010, Nuclear Physics News 5 laboratory report

that is, radioisotopes are used to the exotic ions are accelerated toward examine biomolecules and to perform and directed into an electromagnet in-vivo studies on plants. It is also where they are separated according to planned to test radioisotopes for medi- their mass. cal applications. ISOLDE provides two target sta- ISOLDE also hosts experiments tions, the GPS and the HRS front-end, that investigate fundamental interac- named after the two adjacent mass tions. Especially Penning trap experi- separators. In principle, both front- ments are dedicated to fundamental ends are compatible such that targets tests since they are able to provide can be mounted on either one of the very precise data that are needed to target stations. However, with the further push the limits for new high-resolution separator (HRS) a physics beyond the Standard Model. resolving power of the order of 5,000 or higher can be achieved since two Radionuclide Production and electromagnets are being used. In Operation at ISOLDE addition, a slit system after the HRS The radioactive nuclei are pro- allows one the removal of isobaric Figure 2. Standard ISOLDE target duced in reactions of high-energy pro- contamination if separated in the HRS unit. tons from the PS-Booster accelerator but still present in the beam. The gen- in thick targets. The typical proton eral purpose separator (GPS) can reach energy is 1.4 GeV, which can be low- a resolving power of about 1,000. nuclides as well as properties of ered to 1 GeV on request. Depending Nevertheless, with a special deflector nuclides along the drip lines, includ- on the isotopes of interest and possi- geometry within the mass separator it 11 ing halo nuclei like Li, are of inter- ble isobaric contamination, the target is possible to deliver beam to three dif- est. Furthermore, exotic radioactive material and the subsequent ion ferent beam-lines at the same time: decay modes are investigated. source are chosen to match the experi- while the central mass is sent to the Another closely related field of mental requirements (i.e., mainly pro- main experimental beam-line, the ions research is nuclear astrophysics. duction yield and purity). More than on the lower mass and higher mass Nuclear masses and half-lives of 25 different target materials are side can be send to the GLM and exotic nuclides need to be known in offered with uranium carbide being GHM beam-lines, respectively. order to calculate nucleosynthesis pro- the most versatile and the most The experiments can request cesses. In addition, decay properties requested in the last years. A technical either the GPS or the HRS system including beta-delayed particle emis- drawing of a standard ISOLDE target depending on the experimental con- sion have to be understood in order to unit is shown in Figure 2. straints. With the installation of the take them into account in the theoreti- In general, the target material is ISCOOL cooler and buncher right cal models. Finally, low-energy reac- kept at an elevated temperature, in the behind the HRS separator, a further tion cross-sections provide valuable case of uranium carbide at 2,000°C, constraint for ISOLDE experiments input for the understanding of the vari- so that the produced exotic atoms dif- has been added. While the ISCOOL ous processes in stars. fuse out of the target into an adjacent system provides a better beam emit- The application of radionuclides in ion source. The ionization takes place tance and the possibility of short solid state physics and life sciences is in a hot plasma, on a hot surface, or bunches of a few microsecond another very active field at ISOLDE. by laser excitation. With a careful length, the transmission for light ions Many radionuclides can be provided combination of the target material and below mass A = 40 can be lower than that act as probes to study surface and the ion source type, a chemical selec- 50%. Usually, the beam requests are bulk properties, diffusion of atoms into tivity may be obtained, thus resulting discussed with the ISOLDE technical lattices, and properties of semiconduc- in a selective production of more than group and the Physics Coordinator in tors. Similar experimental techniques 70 of the chemical elements. The ion order to find the most suitable front- are used for biophysics experiments, source is elevated to 30–60 kV and end for the envisaged physics run.

6 Nuclear Physics News, Vol. 20, No. 4, 2010 laboratory report

Target and Ion Source Development Throughout its existence ISOLDE has been leading developments in the production of radioactive isotopes via the ISOL (Isotope Separation On-Line) method. Many results have also emerged on specialized techniques for manipulation of (radioactive) ions and measurements performed with them. It is therefore vital to include dedicated target and ion-source development test runs in the physics on-line schedule. The intensity of a radioactive beam depends on the intensity of the primary proton-driver beam, the target thickness, the cross section for production of the specific radioactive isotope, and on the efficiency of extracting the produced isotope from Figure 3. RILIS scheme with the new solid state pump lasers. the target, purifying it, ionizing it and guiding it into the experimental setup. Many specialized targets and ion chemical selectivity, that is, the or yttrium oxide). First on-line tests sources have been constructed over absorption on a piece of quartz that is and full experiment runs showed very the last years in order to optimize the inserted between the target container promising results [6] and the reliabil- efficiency. However, it is still chal- and the ion source, inside the transfer ity will be further tested in the future. lenging to predict the behavior of a line [4]. Especially the amount of alka- new target design in the fierce envi- lis like rubidium is reduced by several A New Versatile Arc Discharge Ion ronment involving high-temperature orders of magnitude. For an optimal Source (VADIS) chemistry and intense radiation. operation, the temperature of the trans- The production yield also depends Besides the intensity of radioactive fer line has to be adjusted. With such a on a high ionization efficiency. A ion beams, the amount of contamina- target it was possible to obtain very recent technical development aimed tion, that is, the beam purity is of impor- pure beams of neutron-rich zinc iso- at the improvement of a plasma ion tance for the experiments. Presently, topes beyond the magic shell N = 50. source [7]. With this new type of ver- Thierry Stora from the EN-STI group at satile arc discharge ion source CERN is responsible for new target and Application of Submicron Targets (VADIS), the yields of noble gas iso- ion-source developments at ISOLDE. One challenge of the thick ISOL topes have been increased by up to an Especially requests for new beams in targets is the fast release of short- order of magnitude. It was therefore approved experiment proposals and let- lived isotopes from the target con- possible to reach very neutron-rich ters of intent are taken into account to tainer. Especially refractory elements isotopes of krypton and radon, espe- prioritize the projects. Recent highlights like vanadium are not accessible with cially 229Rn was investigated for the of target and ion-source development ISOL targets. However, a recent first time including the determination comprise the following subjects. development toward new target mate- of its mass and half-life [8]. rial showed a way to improve release Beam Purification by Application of times and to provide higher produc- a Quartz tion yields and even new beams. This RILIS Developments This development aims at a reduc- new material consists of sub-micron The Resonance Ionization Laser Ion tion of contaminating ions by use of size grains [5] (e.g., of silicon carbide Source (RILIS) [9] is very selective and

Vol. 20, No. 4, 2010, Nuclear Physics News 7 laboratory report

lasers in order to check the feasibility background effects by orders of mag- for a future use at ISOLDE. nitude. For all experiments the emit- Presently, 29 RILIS elements are tance of the HRS beam has improved available at ISOLDE and for other 17 due to ISCOOL, which allows the elements the ionization schemes have experiments to have a better injection been tested. Recent highlights of RILIS of the beam into the setups. developments include a new scheme for Recently, the HRS front-end was manganese and a two times higher effi- exchanged with a new more modular ciency for gallium. In 2010 it is planned system (Figure 4) and it is planned to to perform an on-line test for resonant exchange the GPS front-end soon. Tar- laser ionization of astatine. get changes and operation should be Besides the broad-band excitation, more reliable with fewer delays. For it is also possible to have a narrow- the beam diagnostics a new fast tape band excitation in order to excite station is being commissioned. It will hyperfine levels and thus select iso- allow the ISOLDE technical group to Figure 4. New HRS front-end FE 6. mers of an isotope of interest by obtain yield information of short-lived tuning the lasers depending on the isotopes not possible with the present spins of the different isomers. It was system. Finally, the vacuum system operates through stepwise excitation also possible to apply the RILIS lasers was completely renovated to ensure a of atoms to above the ionization for in-source laser spectroscopy [12]. more reliable operation. threshold. It has been an important In addition to the upgrade of the part of ISOLDE since 1992 and the RILIS pump lasers, a new off-line lab- Experimental Installations at technology has been transferred to oratory was initiated: the LARIS labo- ISOLDE and Recent Results many other laboratories. The RILIS ratory at CERN. In principle, it This facility portrait cannot pro- group, led by Valentin Fedosseev, is consists of an oven to produce an vide a complete overview of all recent continuously pushing the develop- atomic beam from a sample that is then ISOLDE experiments and results. In ment and tests of new ionization crossed by laser beams for ionization. the following the major permanent schemes [10] in order to get access to The amount of ionization is measured installations at ISOLDE are briefly new elements (e.g., gold [11]) or to with a time-of-flight spectrometer with reviewed and recent examples of improve the laser ionization effi- which the ions are detected and ana- physics results are given. ciency for available elements. lyzed. This off-line laboratory has A recent major upgrade was done proven to be very useful in finding new REX-ISOLDE and Post-Accelerated in light of the HIE-ISOLDE project ionization schemes especially for the Beams (see below). New solid state pump application of the new Nd:YAG pump The REX-ISOLDE system [14] lasers (Nd:YAG) replaced the aging lasers at the ISOLDE RILIS. has evolved in the last years into a copper vapor lasers, which had a facility within the ISOLDE facility rather long start-up time (more than Recent Improvements of the (Figure 5). It is maintained by CERN two hours) and pulse-to-pulse insta- Facility staff and step-by-step the operation has bilities. In 2008 the first on-line use of The ISOLDE facility has over the improved over the last years with Nd:YAG lasers took place and in last years continuously improved the respect to reliability and efficiency. Iso- 2009 only Nd:YAG pump lasers were conditions for experiments. The instal- topes as heavy as radon isotopes have used for on-line runs (see Figure 3 for lation of the radiofrequency quadru- been post-accelerated and efficiencies the laser scheme of RILIS). The cop- pole cooler and buncher ISCOOL reach between 5 and 10%. per vapor lasers have been removed [13], as part of the HIE-ISOLDE The multiply charged ions needed recently and a further upgrade of the upgrade, had a major impact on many for efficient post-acceleration are pump lasers and installation of new experiments. Especially laser spec- produced in a unique way in the dye lasers is ongoing. It is also troscopy experiments can make use of REX-ISOLDE low energy stage. Singly planned to perform tests on Ti:Sa the bunched beams in order to reduce charged ions from ISOLDE are

8 Nuclear Physics News, Vol. 20, No. 4, 2010 laboratory report

stopped, bunched, and cooled in a Penning trap (REX-TRAP), transferred to an electron beam ion source (REX- EBIS) where they are bred to mass-to- charge ratios between A/q = 3 and 4.5 before magnetic separation and acceleration. This essentially universal scheme allows post-acceleration of most of the beams produced by ISOLDE. The technical improvements include tests of diamond detectors for a better beam diagnostics and bunched injection from the ISCOOL buncher and cooler. Furthermore, REX-TRAP has been used to improve the mass- selectivity and within the REX-EBIS charge breeder iron isotopes were produced by in-trap decay of stored Figure 5. REX-ISOLDE setup within the ISOLDE experimental hall. manganese isotopes [15]. The main user of the post- accelerated beams is the MINIBALL gamma array [16]. MINIBALL con- Another beam-line is connected to end of 2010, the COLLAPS experiment sists of eight cryostats, each contain- the REX-LINAC in order to send has a long record of measurements caring three individual germanium post-accelerated beams to dedicated ried out in the last decades at ISOLDE. crystals that are mounted in close experimental setups (e.g., to perform COLLAPS uses different detec- geometry around the target position. scattering experiments). It is also tion techniques to obtain information In case of Coulomb excitation experi- planned to study polarized nuclei on hyperfine splitting or isotope ments (see, Refs. [17–19]) the spheri- using the tilted foils polarization tech- shifts. The most common is the classi- cal target and detection chamber is nique. A test setup is presently cal collinear laser spectroscopy where equipped with a double sided silicon installed at ISOLDE. fluorescence light emitted by the strip detector (DSSSD) to detect pro- excited atoms is detected with photo- jectile and/or target particles. The Laser Spectroscopy at COLLAPS multipliers. The other methods use DSSSD allows one to determine the and CRIS optical pumping, for example, into energy (velocity) and scattering angle Atomic-beam experiments with excited states with a lower ionization of the detected particles, an essential radioactive ions were pioneered at energy (for subsequent re-ionization) ingredient for the Doppler correction ISOLDE and still provide important and or to change the population with of the gamma-ray spectrum. It is also model independent information on respect to nuclear polarization. In the possible to study nucleon transfer nuclear ground state properties such as latter case the beta-NMR technique is reactions in inverse kinematics for charge radius, spin, magnetic dipole applied for the measurement of reso- which dedicated detection set-ups moment, and electric quadrupole nances (see, Ref. [23]). Recent high- have to be used in addition to the moment. Today most studies involve lights comprise results on the charge gamma array. One example is the T- collinear laser spectroscopy where the radii of neutron-rich beryllium iso- REX system [20], which has been ion (or atom) beam is overlaid with one topes [24], on the moments of neu- successfully used to investigate one or or more laser beams. At ISOLDE, two tron-rich gallium isotopes [25], and two neutron transfer reactions (see, experiments are permanently installed: data obtained for nuclear spins and Ref. [21]). An overview of the REX- COLLAPS and CRIS. While the CRIS magnetic moments of copper iso- ISOLDE experimental program can experiment is presently commissioned topes [26]. The CRIS setup (collinear be found in Ref. [22]. and will receive its first on-line beam resonant ionization spectroscopy)

Vol. 20, No. 4, 2010, Nuclear Physics News 9 laboratory report

aims at francium isotopes with low the recoil energy spectrum after beta detectors. They are ideal for establish- production yields of only a few hun- decay of selected isotopes in order to ing decay schemes but unfortunately dred atoms per pulse, which requires search for scalar or tensor contribu- have very limited detection efficiencies. the application of the ISCOOL tions to the Weak Interaction [29]. For As a result it is difficult to determine buncher, pulsed excitation lasers as unpolarized nuclei the shape of the beta-decay strengths because of the well as sensitive particle detection. recoil ion energy spectrum is deter- so-called Pandemonium effect [33]. mined by the β–ν angular correlation. This difficulty can be overcome High-Precision Mass Measurements A Penning trap is employed to act as a by the use of Total Absorption spec- with ISOLTRAP source for the decaying nuclides. By troscopy [34]. The technique is based The ISOLTRAP Penning trap mass use of a so-called MAC-E filter (retar- on the detection of all of the gamma spectrometer [27] aims at the precise dation spectrometer), all recoiling cascades that follow the beta decay and accurate determination of atomic ions are transmitted along the experi- from each level with a highly efficient masses of exotic nuclides. It is capable ment axis and with an electrostatic device, a total absorption gamma to study nuclides with a production yield barrier (retardation potential), their spectrometer (TAS). Thus instead of below 100 ions per pulse and with half- kinetic energy can be determined. The detecting the individual gamma rays lives below 100 ms. The mass determi- experiment has completed the com- one measures directly the intensity of nation is performed by measuring the missioning phase and a physics run on feeding to each level. cyclotron frequency in a strong homo- 35Ar is planned at the end of 2010. The TAS setup at ISOLDE has geneous magnetic field of the isotope of been installed by a collaboration of interest and of a well-known nuclide. groups from Strasbourg, Valencia, Nuclear Orientation at NICOLE From the ratio of the frequencies, the Surrey, and Madrid. This LUCRECIA The NICOLE experiment aims at, mass ratio is obtained. ISOLTRAP setup is one of the largest single crys- e.g., the measurement of magnetic employs meanwhile four different ion tal total absorption spectrometers in dipole moments by use of oriented traps in order to study exotic nuclides. existence. It has a cylindrical shape nuclei at low temperatures and on-line With a linear radiofrequency buncher with a diameter of 38 cm and a length β-NMR [30, 31]. The exotic nuclides and cooler the ions delivered by of 38 cm. It has a longitudinal bore from ISOLDE are deposited, for exam- ISOLDE are bunched for subsequent perpendicular to the symmetry axis. ple, on a pure iron foil soldered to the injection into a multi-reflectron time-of- The beam-line from ISOLDE enters cold finger of the dilution refrigerator flight system. This new device has a this hole and radioactive species can for which the temperature can be low- high resolving power (several 10,000 be implanted directly in the center of ered down to 10 mK. Beta detectors are within a few milliseconds) and pre- the TAS or can be carried there after placed at 0° and 180° to the orientation selects the ions for the first Penning trap, implantation on a moving tape. axis outside the setup close to the sam- where an additional isobaric cleaning is LUCRECIA has been used in ple location in order to measure the performed. Finally, in the measurement studies of shape effects in the mass polarization. The magnetic resonance is Penning trap, the cyclotron frequency region A = 70. For example, it was obtained by varying a radiofrequency of—in the ideal case—only one ion is shown [35] that 76Sr is one of the most excitation and observing a change of the measured. With ISOLTRAP more than deformed, prolate nuclei that exist in asymmetry. One recent example is the 400 nuclide masses have been deter- nature and it was confirmed that 74Kr case of 71Cu, for which the magnetic mined in the last years, which are has a mixed shape ground state [36]. dipole moment was determined for the applied for nuclear structure physics Presently, similar studies in the lead ground state [32]. (see, Ref. [28]), nuclear astrophysics, region aim to determine the shapes of and fundamental tests. One recent high- the ground states of 188,190,192Pb. light is the discovery of the new isotope Spectroscopy at TAS 229 Rn of radon [8]. Measuring beta decay strengths is Free Beam-Lines for Decay notoriously difficult because of the Spectroscopy The WITCH Experiment continuous nature of the beta decay ISOLDE provides two beam lines, The WITCH experiment aims at a spectrum. In general, such measure- LA1 and LA2, for a versatile use of test of the Standard Model by probing ments have been made with germanium the variety of radioactive ion beams

10 Nuclear Physics News, Vol. 20, No. 4, 2010 laboratory report

for any short-term experiment. Usu- have been undertaken in a large vari- While the investigation of new radio- ally these are decay spectroscopy ety of semiconductors and oxides, for isotopes for small-scale clinical stud- setups that are put up in a few days example ZnO [42]Fe. Recently, ies is continued in the near future, and operate on-line up to one week Mössbauer spectroscopy including a biophysics studies using the PAC before they are dismantled. measurement of the angular depen- technique are successfully ongoing dence was used to determine that the with the main probe nuclei 199mHg and The Solid State Physics Program at coupling in ZnO is clearly paramag- 111mCd. The biophysics PAC experi- ISOLDE netic, therefore reducing the perspec- ments generally aim to identify the The application of radionuclides tives for ZnO:Fe to act as a true dilute binding sites, ligands, and dynamic produced at ISOLDE in materials sci- magnetic semiconductor [43]. interactions of probe atoms attached ence and biophysics account for about The method of perturbed angular to large biomolecules under specific 15% of the allocated on-line operation correlation (PAC) allows one to mea- conditions [47]. The radioisotopes are [37–40]. In the case of materials sci- sure the electric field gradient and the implanted in ice held at liquid nitro- ence, investigations focus on the magnetic field that a suited probe gen temperature. After melting the study of semiconductors and oxides, nucleus experiences on its lattice site in ice, the radioactive probes are directly with the recent additions of nanoparti- a solid. Experiments at ISOLDE mainly available for biochemical processing cles and metals, while the biophysics concentrate on the investigation of in aqueous solution using a small studies address the toxicity of metal semiconductors and metal surfaces [44] chemistry lab located on-site. It is ions in biological systems. The differ- using, for example, the probes 111In, planned to extend the ISOLDE bio- ent experimental techniques that are 111mCd, and 111Ag. The general goal is to physics experiments to in vivo studies, used to characterize the samples are better characterize the properties of In, that is, by introducing the PAC probes typical radioactive probe techniques Cd, and Ag impurities in nitrides. PAC into living plants [48]. such as Mössbauer spectroscopy [41], is also applied to study oxides, for perturbed angular correlation, emis- example, for the investigation of phase Outlook: The HIE-ISOLDE Project sion channeling, and tracer diffusion transitions in manganites [45]. The HIE-ISOLDE project is the studies. In addition to these “classic” The principle of the emission next major upgrade and will boost methods of nuclear solid state physics, channeling (EC) lattice location ISOLDE to higher energies for the also standard semiconductor analysis method relies on doping single crys- post-accelerated radioactive ion beams techniques such as photoluminescence tals with radioactive probe atoms that and with an increase of the intensity of or deep level transient spectroscopy decay by the emission of charged par- the proton driver higher production − + profit from the application of radioac- ticles such as α, β or β particles or yields are envisaged. Furthermore, the tive isotopes. conversion electrons, which, on their beam quality is subject to improvement, Mössbauer spectroscopy yields way out of the crystal, experience which is partly accomplished with the information on the charge state and on channeling or blocking effects along installation of the ISCOOL buncher and the electric field gradients and mag- crystal directions. The resulting aniso- cooler as well as the new RILIS pump netic fields to which the Mössbauer tropic particle emission yield in the lasers as mentioned earlier. probe nucleus is exposed in a solid. vicinity of major crystallographic The HIE-ISOLDE project has With the pure and intense 57Mn beams directions depends in a characteristic been approved by the CERN delivered by ISOLDE, it is possible to way on the lattice sites occupied by Research Board in December 2009 populate the 98 ns level in 57Fe by the emitter atoms and is recorded with and the project has officially started beta decay, which is the most com- the aid of position sensitive detectors. in January 2010. With Yacine Kadi monly used Mössbauer state. The During the last years the EC experi- as Project Leader and Matteo Pasini intense 57Mn beams allow the experiments focused on the lattice location of as technical coordinator for the HIE- ments to do fast data taking and to dopants and impurities in ZnO [46], Si, LINAC system the project is looking record hundreds of Mössbauer spectra GaN, AlN, and, most recently, also forward to the production of the first per day, which is not possible in any in Ge. cryomodule. In June 2010 over other radioactive ion beam facility. Biophysics and medical applications 30 Letters of Intent for the future Mössbauer experiments with 57Mn57 have a long tradition at ISOLDE. HIE-ISOLDE facility were evaluated

Vol. 20, No. 4, 2010, Nuclear Physics News 11 laboratory report

by the INTC. The information gath- 9. B. A. Marsh et al., Hyperfine Interact. 34. A. Algora et al., Eur. Phys. J. A 20 ered from the experiment proposals 196 (2009) 129. (2004) 199. will be used to finalize the layout of 10. V. N. Fedosseev et al., Hyperfine 35. E. Nácher et al., Phys. Rev. Lett. 92 the new HIE-ISOLDE experimental Interact. 162 (2005) 15. (2004) 23250. 11. B. A. Marsh et al., Hyperfine Interact. 36. E. Poirier et al., Phys. Rev. C 69 hall. It is planned to operate the low- 171 (2006) 109. (2004) 034307. energy ISOLDE experiments during 12. H. De Witte et al., Phys. Rev. Lett. 98 37. U. Wahl, Nucl. Instr. and Meth. B, to the installation of the new supercon- (2007) 112502. be published. ducting HIE-LINAC accelerator and 13. H. Franberg et al., Nucl. Instr. and 38. J. G. Correia, Nucl. Instr. and Meth. B for the post-accelerated beams a Meth. B 266 (2008) 4502. 136 (1998) 736. staged approach is foreseen in order 14. D. Voulot et al., Nucl. Instr. and Meth. 39. M. Deicher et al., Eur. Phys. J. A 15 to give beam to, for example, MINI- B 266 (2008) 4103. (2002) 275. 15. J. Van de Walle et al., Eur. Phys. J. A 40. M. Deicher et al., Hyperfine Interact. BALL at intermediate energies 42 (2009) 401. 151/152 (2003) 105. before reaching the design value of 16. J. Eberth et al., Progr. Part. Nucl. 41. G. Weyer, Hyperfine Interact. 177 10 MeV/u. Phys. 46 (2001) 389. (2007) 1. With the ongoing development of 17. J. Van de Walle et al., Phys. Rev. Lett. 42. G. Weyer et al., J. Appl. Phys. 102 radionuclide beams, present experi- 99 (2007) 142501. (2007) 113915. ments as well as new installations, 18. I. Stefanescu et al., Phys. Rev. Lett. 43. H. P. Gunnlaugsson et al., Appl. Phys. especially for HIE-ISOLDE, the 100 (2008) 112502. Lett. (2010), 142501. 44. M. Deicher et al., Physica B 389 ISOLDE facility is looking forward to 19. A. Ekström et al., Phys. Rev. Lett. 101 (2008) 012502. (2007) 51. new discoveries and results in the 20. V. Bildstein et al., Progr. Part. Nucl. 45. A. M. L. Lopes et al., Phys. Rev. Lett. next years to come. Phys. 59 (2007) 386. 100 (2008) 155702. 21. K. Wimmer et al., Phys. Rev. Lett., 46. U. Wahl et al., Phys. Rev. Lett. 95 Acknowledgments accepted. (2005) 215503. The following persons provided 22. P. van Duppen and K. Riisager, to be 47. L. Hemmingsen et al., Chem. Rev. 104 material for the article and their support published in J. Phys. G. (2004) 4027. 48. U. Heinz et al., Chem. Eur. J. 15 is acknowledged: Alejandro Algora, 23. D.T. Yordanov et al., Phys. Rev. Lett. (2009) 7350. Yorick Blumenfeld, Kieran Flanagan, 99 (2007) 212501. 24. W. Nörtershäuser et al., Phys. Rev. Björn Jonson, Bruce Marsh, Stefano Lett. 102 (2009) 062503. Marzari, Thierry Stora, Piet van Dup- 25. B. Cheal et al., Phys. Rev. Lett. 104 pen, and Ulrich Wahl. (2010) 252502. 26. K. T. Flanagan et al., Phys. Rev. Lett. References 103 (2009) 142501. 1. Hyperfine Interact. 129 (2000) 1-553. 27. M. Mukherjee et al., Eur. Phys. J. A 2. http://cern.ch/isolde 35 (2008) 1. 3. http://www.scholarpedia.org/article/ 28. S. Naimi et al., Phys. Rev. Lett. 105 TheISOLDEfacility (2010) 032502. 4. E. Bouquerel et al., Nucl. Instr. and 29. V. Yu. Kozlov et al., Nucl. Instr. and Meth B 266 (2008) 4298. Meth. B 266 (2008) 4515. 5. T. Stora et al., Patent # WO2010/ 30. J. Rikovska et al., Phys. Rev. Lett. 85 034364. (2000) 1392. 6. S. Fernandes et al., J. Nucl. Mat., 31. V.V. Golovko et al., Phys. Rev. C 70 accepted (2004) 014312. 7. L. Penescu et al., Rev. Sci. Instrum. 81 32. N.J. Stone et al., Phys. Rev. C 77 (2010) 02A906. (2008) 014315. 8. D. Neidherr et al., Phys. Rev. Lett. 102 33. J.C. Hardy et al., Phys. Lett. B 71 ALEXANDER HERLERT (2009) 112501. (1977)307. CERN

12 Nuclear Physics News, Vol. 20, No. 4, 2010 feature article

Weak Decay of Hypernuclei

ELENA BOTTA Dipartimento di Fisica Sperimentale, Universita’ di Torino, Torino, Italy

STEFANIA BUFALINO INFN—Sezione di Torino, Torino, Italy

Introduction will indicate the mesonic decay widths of reactions (1) and Hypernuclei are nuclear systems in which a hyperon, (2) for a Λ bound in a nucleus, that is for the hypernucleus. normally a Λ, acts as a constituent particle, so that they can In NMWD the decay of the hypernucleus occurs be considered as strange nuclei. They were observed for through processes that involve a weak interaction of the Λ the first time in 1953 by Danysz and Pniewski [1], studying with one or more nucleons. Sticking to the hadronic vertex images from a photographic emulsion stack exposed to Λ → πN, if the emitted pion is virtual it can be absorbed by cosmic rays at an altitude of about 26 km. the nuclear medium, resulting in a non–mesonic decay of These strange nuclear systems, referred to as Λ-hypernuclei, the following types: can be produced in their ground state or in excited states Λ → Γ decaying with both particle and gamma ray emission, n nn ( n) one neutron induced NMWD (1n) (3) depending on the excitation energy as for normal nuclear Λ → Γ p np ( p) one proton induced NMWD (1p) (4) systems. On the other hand, Λ-hypernuclei undergo a sub- (1)ΛNN → nNN (Γ ) two nucleon induced NMWD (2N) (5) sequent decay from the ground state, due to the Λ particle 2 instability for weak decay with a lifetime τ = 263 ps; this Λ where Γ , Γ , and Γ indicate the corresponding decay process is indicated as the decay of L-hypernuclei and has n p 2 widths. Reactions (3)–(5) are not accessible for free Λ and been studied quite extensively both experimentally and can occur only in nuclei. The emitted nucleons carry a high theoretically since the early days of hypernuclear physics momentum (~420 MeV for reactions (3) and (4), ~340 [2,3]. Being the Λ the lightest hyperon, its decay can pro- MeV/c for reaction (5) if the available energy is equally ceed only through the weak interaction, strangeness non- split among the final nucleons), so the NMWD is not Pauli conserving, and consequently the decay of Λ-hypernuclei blocked in hypernuclei and becomes the dominant decay is a weak process, analogous at some extent to the weak mechanism starting from mass number A~5. beta decay of normal nuclei. The total weak decay rate of a Λ–hypernucleus is then: A Λ-hypernucleus in its ground-state decays to non- strange nuclear systems through the mesonic (MWD) and Γ =Γ + Γ (6) non-mesonic (NMWD) weak decay mechanisms. In MWD T MWD NMWD the Λ hyperon decays to a nucleon and a pion in the nuclear Γ =Γ + Γ where MWD π− π0 is the total mesonic weak decay medium, similarly to the weak decay mode in free space: Γ =Γ + Γ rate and NMWD 1 2 , is the total non-mesonic weak Γ =Γ +Γ decay rate, with 1 n p; the hypernucleus lifetime is Λ → + π− + τ=/Γ . free p 37.8 MeV (64.2 %) (1) T The observables that can be obtained from the experi- → n + π0 + 41.1 MeV (35.8 %) (2) ments are the hypernucleus lifetime, τΛ, the decay ampli- Γ Γ Γ Γ Γ tudes for the different channels, n, p, 2, π−, π0, the in which the emitted nucleon (pion) carries a momentum Γ Γ ratio n/ p and the energy distributions of the light decay ~100 MeV/c. MWD is suppressed in hypernuclei with products, while daughter nuclei produced in reactions (1)–(5) respect to the free-space decay, due to the Pauli principle, can hardly be detected. being the emitted nucleon momentum smaller than the In this article the hypernuclear systems will be indi- A nuclear Fermi momentum (~270 MeV/c) in all nuclei cated by the symbol ΛZ, where A indicates the mass num- Γ Γ except for the lightest ones. In the following π− and π0 ber of the system, that is, the total number of “nucleons”

Vol. 20, No. 4, 2010, Nuclear Physics News 13 feature article

300 It should be noticed that all the experimental data show free Λ lifetime a smoothly decreasing behavior as a function of the mass 250 number A, with the exception of the value for 16O and that for the heavier targets (Au, Bi, U: A ~ 215). The conclu- 200 sion is that for the medium A hypernuclei τ is about 80% that of the free Λ, falling at about 50% for the heaviest tar- 150 gets. This result indicates that in medium A hypernuclei

lifetime (ns) the opening of the NMWD channels compensates almost 100 completely the suppression of the MWD ones due to the Pauli blocking, while in heavy hypernuclei the NMWD 50 process dominates and reduces the stability of the free Λ. The variation of the Λ lifetime when embedded in a 0 10 102 nucleus represents an in-medium modification of the free mass number A particle properties. Figure 1. Present status of lifetime measurement for L-hypernuclei.

(p, n, Λ), Λ identifies the constituent hyperon and Z stands 300 for the chemical symbol of the atomic species with Z 250 protons. In the following the present experimental knowledge 200 on the weak decay of Λ-hypernuclei is presented and the most recent results published by the FINUDA Collabora- 150

tion are discussed in detail. We just remember that FIN- counts / (2 MeV) 100 UDA [4] was a magnetic spectrometer working at one of + − the two interaction regions of the (e , e ) collider DAΦNE 50 at LNF and that its scientific program was focused on the study of both spectroscopy and decay of Λ-hypenuclei in a 0 wide mass number range (A = 5–51). Present theoretical 0.25 models and calculations describing both MWD and NMWD are addressed to allow the interpretation of the 0.2 results. Recent experimental and theoretical reviews can be 1/2+

Λ 0.15 + found in Refs. [5] and [6]. Γ 3/2 - / π Γ Lifetime Measurements 0.1 The most straightforward observable that can be mea- 0.05 sured is the lifetime τ of a given hypernucleus for weak decay, otherwise referred to as the lifetime of Λ in nuclei. 0 It can be obtained by measuring the delay in the emission 20 25 30 35 40 45 50 55 60 kinetic energy (MeV) of the decay products from the ground state of a specific hypernucleus, neglecting the contributions from hypernu- Figure 2. Upper part: kinetic energy spectrum of MWD p- 7 clei with lower mass number, that can be produced by de- for LLi obtained by the FINUDA experiment (adapted excitation with particle emission of highly excited states of from [8]). The solid curve is a gaussian fit to the peak in that hypernucleus and are indicated as hyperfragments. the spectrum, to compare with theoretical predictions. Recently measurements of τ of reasonable quality Lower part: calculated major decay rates to final 7Be 7 + (errors of ~10%) were performed on a wide mass number states from Ref. [10], in red bars for LLi (1/2 ), and in 7 + range [7] and the results are summarized by Figure 1. blue bars for LLi (3/2 ).

14 Nuclear Physics News, Vol. 20, No. 4, 2010 feature article

Mesonic Weak Decay light s-shell, p-shell, and sd-shell hypernuclei [9] and have The mesonic weak decay channel of Λ-hypernuclei has been reviewed recently [10]. been the tool that allowed the discovery of the strange The energy spectra of MWD π− allow one to get infor- nuclear systems and has been studied both experimentally mation on the spin-parity of the initial hypernuclear ground and theoretically from the birth of Hypernuclear Physics. state. In this respect the study of pion spectra from MWD From the experimental side, a considerable amount of can be regarded as a new spectroscopic investigation tool. Γ Γ Λ data on π− and/or π0 is now available on light -hypernu- Indeed, kinetic energy spectra of the emitted particles are 4 4 5 7 9 11 clei of s- and p-shell: ΛH, ΛHe, ΛHe, ΛLi, ΛBe, ΛB, directly related to the excitation functions of the daughter 12 15 ΛC, ΛN (see Ref. [8] and references quoted therein). It is nucleus and the comparison with spectroscopic calcula- worth underlying that the information available up to a few tions starting from different spin-parity configurations of years ago on the charged MWD of light hypernuclei con- the hypernuclear ground state allows one to discriminate sisted almost entirely of Γπ−/ΓΛ values, where ΓΛ is the free between possible assignments. This is evident in Figure 2 − 7 Λ total decay width, obtained by means of counting mea- where the spectrum of MWD π for ΛLi measured by surements with no magnetic analysis of the decay meson. FINUDA [8] is reported and compared with calculations Recent results from the FINUDA experiment [8] have from Ref. [10]: the shape of the spectrum clearly allows filled this lack of information and will be discussed in the one to determine the spin of the hypernucleus ground state. following. Exploring the possibility of performing a magnetic analysis The theory of hypernuclear MWD was initiated by of MWD pions, FINUDA has confirmed previous spin-par- 7 + 9 + 11 + Dalitz [3], based on a phenomenological Lagrangian ity assignments for ΛLi (1/2 ), ΛBe (1/2 ), and ΛB (5/2 ), describing the elementary decay processes (1) and (2), and obtained by different techniques, and has assigned a 3/2+ 15 motivated by the observation of MWD reactions in the pio- spin to the ΛN ground state, that could not be determined neering hypernuclear physics experiments with photo- with other methods. graphic emulsions, that provided means of extracting Concerning the MWD decay rate, Figure 3 reports the hypernuclear ground-state spins and parities. experimental values of Γπ−/ΓΛ available at present for s- and Γ Γ Complete calculations of π− and π0 for single final p-shell hypernuclei and the theoretical values calculated in states were performed during the 1980s and 1990s for very Refs. [9] and [10]. It is remarkable that a very good agreement holds among the FINUDA results and previous measurements,

0.5 when existing, and among the FINUDA results and theo-

0.45 retical calculations. Very strong nuclear structure effects are also evident, as predicted by Ref. [9]. 0.4 To complete the discussion of MWD, it must be 0.35

Λ noticed that for low-energy pions, the pion-nucleus poten- Γ

-/ 0.3

π π

Γ tial has been studied so far through -nucleus scattering 0.25 experiments and measurements of X-rays from pionic 0.2 atoms; the study of MWD, in which a pion is created by 0.15 the decay of a Λ hyperon deep inside the nucleus offers, 0.1 important opportunities to investigate in-medium pions 0.05 and to discriminate between different off-shell extrapola-

0 tions inherent in potential models. 4 6 8 10121416 A Non-Mesonic Weak Decay - Figure 3. Total p decay rate Gp- in units of GL as a NMWD reactions (3) and (4) actually are weak reac- function of the hypernuclear mass number A. Open tions between baryons inside nuclei. Due to the short Λ 7 9 11 15 circles: LLi, LBe, LB, and LN values measured by lifetime, the NMWD is the only practical way to get infor- FINUDA [8]. Full triangles: previous measurements; mation on the weak process ΛN→NN, that is the first open squares: theoretical calculations from Ref. [9]; full extension of the weak, ΔS = 0, NN → NN interaction, in stars: theoretical calculation from Ref. [10]. particular on its parity-conserving part that is normally

Vol. 20, No. 4, 2010, Nuclear Physics News 15 feature article

NMWD of Λ-hypernuclei has been studied quite extensively both experimentally and theoretically since the early days of hypernuclear physics. See Refs. [5] and [6] for a complete review. Most of the theoretical efforts of the last years were devoted to the solution of a complex situation concerning the weak decay rates: indeed, a strong disagreement between theoretical estimates and experimental determi- Γ Γ nations of the n/ p ratio characterized up to few years Γ ago the so-called Gn/Gp puzzle, for which ( n/ Γ Γ Γ p)theor << ( n/ p)exp. Limited, low precision, data were 12 11 available only for ΛC and ΛB. Recently, in Ref. [13] a Γ Γ value of n/ p ~0.9 was reported, with a 20% error, for 5 12 ΛHe and ΛC from experiments at KEK, by analyzing the spectra of both final state nucleons in coincidence and selecting events not suffering for final-state interaction (FSI). This result is in agreement with recent theoretical values obtained with the inclusion in the ΛN→NN transition potential of mesons heavier than the pion, of interactions terms that explicitly violate the ΔI = 1/2 rule and, in particular, of a description of the short range baryon-baryon interaction in terms of quark degrees of freedom introducing ΔI = 3/2 contributions. Thanks to this convergence between experimental results and theoretical calculations the puzzle can be considered as solved even if quite big errors affect the experimental results; the theoretical model, which 12 Figure 4. Top: comparison between the LC NMWD reproduces at best the results, can be looked at as the proton spectra measured by FINUDA [17] (red circles) best level of understanding at first approximation of the and KEK [16] (blue circles). Bottom: comparison between NMWD mechanism. the FINUDA spectrum and the theoretical calculations of In the interpretation of the decay rate experimental val- Ref. [14] (continuous line histogram) ues it was also pointed out that the 2N induced decay could play an important role in NMWD and that a fraction as big Γ as 20–25% of the NMWD could be due to this mechanism, completely masked by the strong interaction. Since even if no experiment had explicitly measured its contribu- NMWD is characterized by a large momentum transfer it is tion. However, no theoretical calculation explains both the Γ Γ Γ not influenced by the details of hypernuclear structure and NMWD and n/ p values consistently. turns out to be a useful tool to elucidate the role of explicit Still puzzling is the situation concerning the nucleon quark/gluon substructures of the baryons by probing short spectra in NMWD, in particular for protons. Indeed, distances. discrepancies still exist between theory and experiments. A On the other hand, reaction (5) can be interpreted by complete review can be found in Ref. [6] and more recent assuming that the pion is absorbed by a strongly correlated calculations can be found in Ref. [14]. pair of nucleons. This mechanism has been suggested in A large amount of data on NMWD has been produced Γ Γ Ref. [11] to reproduce the observed values of n, p, and by the SKS Collaboration [15] at KEK; see Ref. [5] for a Γ Γ n/ p but no experimental evidence has been obtained up complete review. In Ref. [16] spectra of protons from 5 12 to now of the 2N stimulated decay, with the exception of a NMWD of ΛHe and ΛC are reported with a low-energy few indirect results [12]. cut at 35 MeV.

16 Nuclear Physics News, Vol. 20, No. 4, 2010 feature article

The FINUDA experiment at LNF has obtained can be evaluated, in good agreement with theoretical 5 7 12 NMWD proton spectra for ΛHe, ΛLi, and ΛC [17], calculations [17] and previous indirect experimental 12 with a lower energy cut at ~15 MeV. The kinetic energy determinations [12] for ΛC only. This is the first model- Γ Γ spectra show a similar shape for the three hypernuclei: a independent experimental determination of the 2/ p peak around 80 MeV (which corresponds to about half ratio. of the Q–value for the free Λp→np reaction) broadened To complete the discussion of the results obtained at by the Fermi motion of nucleons and smeared, on its LNF on the weak decay of Λ-hypernuclei, it is worth citing low energy side, by a rise that can be ascribed to FSI that FINUDA has also been able to measure rare two-body and 2N induced weak decays. Figure 4, from Ref. [16], NMWD channels of s-shell hypernuclei/hyperfragments reports the comparison between the spectrum obtained [20], increasing a very poor sample of informations that 12 at KEK for ΛC (triangles) and that obtained at LNF dates back to bubble chamber and emulsion experiments. (dots), normalized beyond 35 MeV, Figure 4 left, and For the first time the relative branching ratio for the decay 4 the comparison between the FINUDA data and the of ΛHe in the dd and pt channels have been measured and 4 4 theoretical calculations by Ref. [14] normalized beyond a ratio R( ΛHe→dd/ ΛHe→pt) = 0.52 ± 0.35 has been 5 15 MeV, Figure 4 right. deduced. Also the decay rate of ΛHe in the dt channel has Γ = ± −3 Γ The comparison between the experimental spectra been obtained: dt (2.9 1.5) 10 Λ in agreement with shows that a quite strong disagreement is present between old theoretical expectations. the two experiments: the peak at 80 MeV is lost in the KEK data, due probably to the large thickness of the target. Conclusions The comparison with theoretical calculations indicates also The study of the weak decay of Λ-hypernuclei is a a strong disagreement of the FINUDA data with the theory. composite field related not only to hypernuclear phys- 5 The situation in less problematic for ΛHe, where a quite sat- ics, but also to nuclear and particle physics: it can be isfactory compatibility exists between both the FINUDA seen as the ground where the two realms overlap. The and KEK data and the FINUDA data and theoretical calcu- strangeness content of the constituent Λ allows for lation of Ref. [14]. investigation of strange nuclear systems as extension of The amount of the contribution of the 2N induced the ordinary non strange ones, and the study of their Γ Γ decay to the total NMWD, 2/ NMWD, seems to be funda- decay can shed light on the modifications of the intrinsic mental in obtaining a good agreement between experimen- properties introduced by the presence of the other com- tal data and theoretical calculations. Various theoretical ponent. The MWD investigation can act as a tool for the papers were dedicated to the calculation of the rates and analysis of the structure of the ΛN interaction potential, the nucleon spectra for this mechanism; a good summary which is the basic ingredient for building the Λ-nucleus on this topic can be found in Ref. [18]. potential. The NMWD is actually the only effective Very recently the FINUDA experiment has per- method to study the weak 4-baryons strangeness chang- formed a complete analysis [19] of the proton energy ing interaction ΛN→NN. 5 7 9 spectra following the NMWD of the ΛHe , ΛLi, ΛBe, In this article the actual knowledge of the weak decay 11 12 13 15 16 ΛB, ΛC, ΛC, ΛN, and ΛO hypernuclei. A clear of hypernuclei has been presented and discussed with the trend was found in the proton energy spectra as a func- help of theoretical models. tion of the mass number: the shape of the spectra After the end of the operation of the FINUDA experi- remains similar to that of Figure 4, but the peak at ~80 ment at LNF, the study of hypernuclear physics will MeV is more and more blurred as A increases and the continue at J-PARC [21], the new accelerator complex, that contribution of the low energy component ascribed to has just started its operation. A substantial part of the scien- FSI and 2N induced decay becomes more and more tific program for the first operating period is focused on the important. study of strangeness nuclear physics, in particular on the Exploiting the systematics on A, a model-independent spectroscopic study of Ξ–hypernuclei and on the comple- analysis of the contributions of FSI and 2N induced tion of the gamma- ray spectroscopy of light hypernuclei. decays to the nucleon spectra has been performed. A Measurements on the weak decay of hypernuclei are Γ Γ = ± = ÷ value 2/ p 0.43 0.25 for the A 5 16 range has been planned for the second operation period, in a couple of years Γ Γ = ± obtained, from which a value of 2/ NMWD 0.24 0.10 from now.

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References 1. M. Danysz and J. Pniewski, Philos. Mag. 44 (1953) 348. 2. W. Cheston and H. Primakoff, Phys. Rev. 92 (1953) 1537; M. M. Block and R. H. Dalitz, Phys. Rev. Lett. 11 (1963) 96. 3. R. H. Dalitz, Phys. Rev. 112 (1958) 605; R. H. Dalitz and L. Liu, Phys. Rev. 116 (1959) 1312; R. H. Dalitz, Nucl. Phys. 41 (1963) 78. 4. T. Bressani, Nucl. Phys. News 6 (1996) 8; M. Agnello et al., Nucl. Instr. Meth. A 537 (2007) 205. 5. H. Outa in Hadron Physics, Proceedings of the International School of Physics “Enrico Fermi,” Course CLVIII, T. Bressani, U. Wiedner, and A. Filippi, Eds. (IOS Press, Amsterdam, 2005), p. 219. 6. W. M. Alberico and G. Garbarino, Phys Rep. 369 (2002) 1. 7. H. Outa et al., Nucl. Phys. A 639 (1998) 251c; K. J. Nield et al., Phys Rev. C 13 (1976) 1263; W. Cassing et al., Eur. ELENA BOTTA Phys J. A 16 (2003) 549 and references quoted therein. 8. M. Agnello et al., Phys. Lett. B 681 (2009) 139 and references quoted therein. 9. T. Motoba and K. Itonaga, Progr. Theor. Phys. Suppl. 117 (1994) 477. 10. A. Gal, Nucl. Phys. A 828 (2009) 72. 11. W. M. Alberico, A. De Pace, M. Ericson, and A. Molinari, Phys. Lett. B 256 (1991) 134. 12. M. Kim et al., Phys. Rev. Lett. 103 (2009) 182502. 13. B. H. Kang et al., Phys. Rev. Lett. 96 (2006) 062301; M. J. Kim et al., Phys. Lett. B 641 (2006) 28. 14. G. Garbarino, A. Parreno, and A. Ramos, Phys. Rev. C 69 (2004) 054603. 15. T. Nagae, Nucl. Phys. News Int. 16 (2007) 3, p. 19. 16. S. Okada et al., Phys. Lett. B 597 (2004) 249. 17. M. Agnello et al., Nucl. Phys. A 804 (2008) 151. 18. E. Bauer and G. Garbarino, Nucl. Phys. A 828 (2009) 29. 19. M. Agnello et al., Phys. Lett. B 685 (2010) 247. 20. M. Agnello et al., Nucl. Phys. A 835 (2010) 439. 21. Nucl. Phys. News Int. 19 (2009) issue 4. STEFANIA BUFALINO

18 Nuclear Physics News, Vol. 20, No. 4, 2010 feature article

Charmonium Spectroscopy—A Tool for Understanding the Strong Interaction

ULRICH WIEDNER Institute for Experimental Physics I, Ruhr-University Bochum, Bochum, Germany

History of quarks (charm) and later the 5th generation (bottom) When brought together, matter and antimatter will that strongly supported the viewpoint that mesons could be annihilate each other, resulting in a state of pure energy. understood in a way similar to positronium in the elec- This energy can then materialize to form new particles. troweak interactions. The resulting potential would contain Energy for the production of particles can also be produced a Coulomb-like part based on a one-gluon exchange in other processes like the inelastic collision of a highly (OGE) and, special to the strong interaction, a part describ- energetic particle with a target, but at a much lower effi- ing the observed confinement: ciency than in the annihilation process. The use of both techniques in November of 1974 led to the so-called 4 a November revolution of physics; a fourth quark, namely Vr()=−s +kr 3 r the charm quark, was found simultaneously at SLAC and at Brookhaven [1, 2] and the quark model became a reality. Theoretical speculations on the existence of a fourth The narrow width of the charmonium states and the fact quark reach back to the year 1970, when Glashow, Iliopou- that they are well separated without interfering among each los, and Maiani predicted its existence in order to explain other allowed for precise calculations from the theoretical the suppression of flavor-changing neutral currents in the side. Even the simple-minded OGE complemented with a weak interaction [3]. The experimental discovery then spin-dependent Breit-Fermi Hamiltonian and a spin-orbit opened the door for the spectroscopic investigation and term gave a very good description of the charmonium classification of matter in a similar way as had been done spectrum as it was known before 2003. The case of char- in atomic physics long before. Physicists identify and clas- monium physics seemed to be closed. sify particles by assigning them quantum numbers, which From the theoretical side, however, it is questionable are properties that are unchanged in an interaction. These whether the concept of “free” gluons is valid in QCD. It include among others the electric charge, the spin, and the seems much more reasonable to describe the binding of baryon number and lepton numbers. the quark–antiquark pair by a flux of multiple gluons con- Following the discovery of the charm quark, more char- fined to a tube due to the gluon self-interaction. This monium states with relatively narrow widths were found in gauge boson-gauge boson interaction is special to the quick succession. The narrow width indicates a long life- strong interaction and does lead to peculiar predictions. time of the states, and results from the fact that charmo- Due to our understanding, bound states containing solely nium states (because their mass lies below the open-charm gluons (glueballs) or states where gluonic excitations of decay threshold at 3.73 GeV, which is twice the mass of the flux tube contribute to the overall features of a bound the D-mesons) must decay through the annihilation of the quark–antiquark pair (hybrids) should exist and we cc pair. The spectroscopic investigation of the experimen- should keep it in mind for the subsequent discussion. tally clean charmonium states deserves major credit in the Since the gluonic self-interaction is at the heart QCD, it development of Quantum Chromodynamics (QCD), the should be especially rewarding to study such glueballs theory of the strong interaction. and hybrids, which are predicted to exist in the charmo- The total widths in these decays have traditionally been nium mass region. described as annihilation into gluons, using the corresponding formulas for positronium annihilation into pho- Surprises from B-Decays α tons but with s vertices and combinatoric color factors. It Interest in charmonium physics got a big boost in 2003, was the spectrum of particles consisting of the 4th generation when the BELLE collaboration found an unexpected, very

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precise determination of the mass and a measurement of the width is a must for the future.

More Exotic Particles One particle that is definitely not a charmonium state or a traditional meson is the Z+(4430), again discovered by BELLE in the Kπ±ψ’ channel (Figure 1) [6]. This state carries electric charge and thus cannot be a charmonium state even though it must, due to its decay into ψ’π+, contain a cc pair. It is an obvious candidate for a multiquark state. Two more things are remarkable about the Z+(4430): its decay into J/ψπ+ is not observed, which might be indicative of a certain selection rule, and the width is again rather narrow. It is exactly this width that lets BELLE rebuke the claim of the BaBar collaboration that instead of being a resonance the signal is caused by interference effects in the Kπ channel. Two more charged states like the Z+(4430) were observed by BELLE but not by other experiments, decay- ± → π+χ + + Figure 1. The p y’ invariant mass spectrum for B K ing into c1 — the Z (4050) and the Z (4250) [7]. p±y’ decays. The fit shows a Breit-Wigner and a phase- Many more states, most of them above the open-charm space-like background. The blue area shows the estimated threshold, have since been found by several experiments. background. Because of their unusual properties or decay patterns they are not considered usual charmonium. Figure 2 gives an overview of the new states in relation to the conventional charmonium spectrum. + − narrow state in the J/ψπ π invariant mass spectrum, called Decay patterns that result in a charmonium state and a X(3872). The properties of this state are light meson instead of decays into open-charm particles raise the question if one or more of these states actually are M =±3871.. 56 0 22 charmonium hybrids. As mentioned earlier, hybrids are quark–antiquark states in which the gluonic degrees of Γ < 23. MeV freedom have been excited and contribute to the overall quantum numbers. It seems very likely that the gluonic The BELLE collaboration gives as a likely JPC assignment excitation decays into a light meson, while the relatively 1++, making it together with the narrow width, which is so heavy charm quarks stay in place and form a charmonium far known only as an upper limit, unlikely to be a conven- state. A good candidate for a charmonium hybrid was tional charmonium state. What else could it be? It is inter- the Y(4260), a state found by BaBar (and subsequently esting to recognize that it lies within 0.5 MeV of the confirmed by Cleo-c and BELLE). The Y(4260) decays + − DD*0 0 threshold, and nowadays we know that it decays into J/ψπ π . The quantum numbers are known from the into J/ψπ+π– and J/ψπ+π–π0 with similar rates. The proxim- production mechanism and must be JPC = 1−− . However the ity to a threshold makes it a prime candidate for a hadronic 1−− states in this mass region are well-known from previ- molecule. Molecules are weakly bound states of at least ous e+e− studies. Such overpopulation is also indicative of two hadrons and nuclei and hypernuclei could be consid- charmonium hybrids. ered as well-known examples. Obviously the characteris- It is worthwhile to turn to the question of how progress tics for a molecule should be that its mass is slightly below could be made in the foreseeable future. In e+e− annihila- the mass of the free constituents due to the binding energy. tions, direct charmonium formation is possible only for Since the interpretation of the state depends critically on states with the quantum numbers of the photon JPC = 1−−, the measured values of the state’s properties, a more namely the J/ψ , ψ′, and ψ(3770) resonances. Precise

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measurements of the masses and widths of these states can • up to ten times higher instantaneous luminosity (L = 2 be obtained from the accurate knowledge of the energies of × 1032 cm−2s−1 in high-luminosity mode, compared to the electron and positron beams. Charmonium states with 2 × 1031 cm−2s−1 at Fermilab); − different quantum numbers can be reached in the decay of • better beam momentum resolution (Δp/p = 10 5 in high- these resonances or, at higher energies, by means of other resolution mode, compared with 10−4 at Fermilab); production mechanisms, such as photon-photon fusion, ini- • a better detector (higher angular coverage, magnetic tial state radiation and B-meson decay. field and the ability to detect the hadronic decay On the other hand, any and all charmonium states can modes). be directly formed in antiproton–proton annihilations. This technique was successfully employed first at CERN and The FAIR antiproton facility was designed keeping these then at Fermilab thanks to the development of stochastic numbers in mind. beam cooling. With this method the masses and widths of all charmonium states can be measured with excellent The Future of Charmonium Spectroscopy accuracy, determined by the very precise knowledge of the Current experiments cannot add much more informa- initial antiproton and proton beams and are therefore not tion because the observed particles are produced in a decay limited by the resolution of the detector. The precision data chain and the knowledge of their properties is largely are necessary to progress further in understanding the con- limited by detector resolution. Where tested, these states ventional charmonium system and the underlying forces. couple strongly to antiproton–proton annihilations as In order to ensure success compared to previous experi- shown by results from LEAR experiments but also from ments a new antiproton facility should have: high-energy Fermilab experiments. In most cases a limited detector resolution will not be an issue at FAIR due to the possibility to directly scan the resonances with a high- precision antiproton beam, allowing PANDA to clarify the nature of the X, Y, and Z states. The appearance of additional narrow states in the charmonium mass region confirms the assumption that the identification of additional states is easier than in the light- quark sector due to reduced mixing. Mixing with conventional mesons is not at all an issue for hybrids with exotic quantum numbers, that is, quantum numbers that cannot be accommodated by a quark–antiquark pair. Several of the lowest-mass charmonium hybrids are predicted to have exotic quantum numbers. While usually the process of a complicated partial wave analysis leaves some ambiguities concerning the identification of an exotic nature, it can be easily established in antiproton–proton annihilations. In a production experiment, where the particle is usually produced together with a light meson, exotic quantum numbers are allowed for the unknown state. A subsequent formation experiment, with the center-of-mass energy of the experiment being exactly the particle mass, should then allow a scan of its properties. The exceptions are particles with exotic quantum numbers, which cannot be reached in a formation experiment. Therefore the appearance of a res- Figure 2. The established charmonium spectrum is shown onance in a production experiment and its absence in a on the left side. On the right side, newly discovered X and subsequent scan shows immediately its exotic nature. Y states with unusual properties and as yet unknown While the BaBar experiment is shut down for good, nature are plotted. BELLE will continue after a major upgrade of the machine

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and the detector. The expected increase in data rate will be In the future, the precision study of these new, unusual a factor of 100. This will allow the possible discovery of charmonium states might reveal deep insights into non- new phenomena exploiting the very same techniques as perturbative QCD and our understanding of the strong BELLE, now with a 100-fold increased sensitivity. It will interaction. not be in competition with PANDA as far as the necessary precision hadron physics, provided the time scales stay Acknowledgments more or less as they are, since it will take SuperBELLE, The author acknowledges the support from BMBF, and coming online 2014–15, several years to accumulate the the GSI and Julich Helmholtz centers for his work. required statistics of several thousand events for a final state to determine its quantum numbers in a partial wave References analysis. PANDA will accumulate these statistics much 1. J. J. Aubert et al., Phys. Rev. Lett. 33 (1974) 1404. faster, and as an antiproton facility, is free from the inher- 2. J.-E. Augustin et al., Phys. Rev. Lett. 33 (1974) 1406. ent problem of being limited by detector resolution or con- 3. S. L. Glashow, J. Iliopoulos, and L. Maiani, Phys. Rev. D2 strained to a specific decay chain. In addition, claims that (1970) 1285. the Z+(4430) is caused by interference of the particles in 4. S. K. Choi et al., BELLE Collaboration, Phys. Rev. Lett. 91 the final state can only be resolved in a different produc- (2003) 262001. 5. K. Abe et al., BELLE Collaboration, arXiv:hep-ex/0505038. tion mode, like the antiproton–proton annihilation, where 6. S.-K. Choi et al. BELLE Collaboration, arXiv: hep-ex/ these particles are simply not present and a direct scan of 0708.1790v2. + the Z (4430) seems possible. 7. R. Mizuk et al. BELLE Collaboration, PR D78 072004. The BESIII experiment in China has started data taking and will dominate the traditional charmonium spectroscopy of JPC = 1−− states that can be done at e+e− colliders in formation mode and the study of their decay products. The data volume and the quality of the detector will be a major step forward in hadron physics. To summarize: charm has once revolutionized our understanding of particle physics and it seems that history might repeat itself again. This is due to the discovery of unconventional charmonium states, which

• have strong decay modes into charmonium states and light mesons, • have a relatively narrow width despite being above the open charm threshold, • seem to have selective decay patterns into either J/ψ or ψ’ but not to both, and • seem to be not present in the total hadronic cross- + − section of e e collisions. ULRICH WIEDNER

22 Nuclear Physics News, Vol. 20, No. 4, 2010 facilities and methods

AGATA and GRETA: The Future of Gamma-Ray Spectroscopy

Introduction germanium crystals each surrounded detection of nuclear electromagnetic High precision gamma-ray spec- by a Compton-suppression shield, have radiation and its sensitivity for select- troscopy is one of the powerful tools pushed this particular detector technol- ing the weakest signals from exotic used to study the structure of excited ogy to its limit, with an efficiency for a nuclear events will be enhanced by a nuclear states and it has contributed to 1 MeV gamma ray of about 10% and a factor of up to 1,000 relative to its the discovery of a wide range of new peak-to-total ratio of 0.5. predecessors (Figure 1). It will have phenomena. Each major advance in With the advent of the first gener- an unprecedented angular resolution, gamma-ray detection has resulted in ation of radioactive-beam facilities resulting in excellent energy resolu- significant new insights into the struc- dedicated medium-sized detector tion even at velocities of the emitting ture of nuclei. To date, these advances arrays (e.g., MINIBALL [3,4] and nuclei up to 50% of the velocity of have culminated in two state-of-the- EXOGAM [5, 6] in Europe, SeGA [7] light by minimizing Doppler broaden- art 4π arrays of escape-suppressed in USA, and GRAPE [8] in Japan) ing. It is superbly suited to be used in spectrometers, Euroball in Europe [1] have been constructed with the spe- conjunction with the new generation and Gammasphere in the United cific aim to study the electromagnetic of radioactive beam accelerators or States [2]. These arrays, which consist radiation from reactions of fast-moving existing stable beam facilities. These of more than a 100 large volume short-lived exotic nuclei. instruments will be vital to realize the The new challenges for nuclear scientific potential of new facilities spectroscopy are emerging principally for example at EURISOL, FAIR, from the new generation of high- FRIB, HIE-ISOLDE, SPES, and intensity radioactive ion beam facilities SPIRAL 2. currently being developed worldwide. Given the importance of this These provide beams with energies increase in sensitivity, collabora- spanning the Coulomb energy regime, tions have been established in the typical of the ISOL facilities (SPI- United States and in Europe to con- RAL, REX-ISOLDE), to the interme- struct 4π tracking spectrometers. In diate and relativistic energy regimes the United States the project is of fragmentation facilities, such as called GRETA (Gamma Ray Energy RIBF at RIKEN, NSCL at MSU, and Tracking Array) [9,10] and in SIS/FRS at GSI. To fully realize the Europe AGATA (Advanced Gamma science potential of these facilities a Tracking Array) [11–13]. Both new generation of high-efficiency these projects have taken the first detectors with improved position res- step with the construction of GRET- olution is required. The global con- INA (Gamma Ray Energy Tracking sensus of opinion is that the next In beam Nuclear Array) and the Figure 1. The sensitivity of various major step in γ-ray spectroscopy AGATA demonstrator. These gamma-ray arrays as a function of involves abandoning the concept of a projects represent major technologi- spin and approximate timescale. physical suppression shield and cal advances in radiation detection Selected nuclear structure phenomena achieving the ultimate goal of a 4π Ge and each has taken a very similar are indicated. The sensitivity is ball through the technique of γ-ray overall approach. This article sum- defined as the inverse of the fraction energy tracking in electrically marizes very briefly the status of of the intensity in a nucleus that segmented Ge crystals [9,10]. The each project and gives examples can be studied by gamma-ray resulting spectrometer will have an from each project in some of the spectroscopy. unparalleled capability for the key technical areas. More details of

Vol. 20, No. 4, 2010, Nuclear Physics News 23 facilities and methods

many experiments involve high recoil In both AGATA and GRETA the Ge velocities), the ability to handle high detectors are 36-fold segmented multiplicities without summing (as coaxial Ge crystals. The crystals interactions from different gamma have a length of 9 cm and a diameter rays can be resolved), and the ability of 8 cm at the rear. At the front they to pick out low-multiplicity events are tapered to a hexagonal shape with hidden in a high background environ- a tapering angle of about 8° for ment due to the possibility of reject- AGATA and 10° for GRETA. These ing background events using the angles are a result of the efficient Figure 2. The AGATA spectrometer at directional information of the radia- packing of the detectors in a 4π Legnaro. The picture shows 5 triple tion. Another asset is that the high geometry. The geometry is based on cryostats, each with three Ge capsules. segmentation plus tracking also tiling a sphere with the geodesic One of the outer end caps is removed makes high precision linear polariza- arrangement of irregular hexagons to indicate the Ge capsules. tion measurements possible. The mod- and regular pentagons; for AGATA ularity of the detector design makes it the full array comprises 180 hexa- extremely versatile and flexible for use gons and 12 pentagons and GRETA each project can be found in Refs. in many different configurations. 120 hexagons and 12 pentagons. [10,14]. The new technological advances These geometries result in 3 slightly that make the tracking spectrometer different crystal shapes for AGATA Principle of Gamma-Ray Tracking possible are: fabrication of highly and 2 for GRETA. Each crystal is The improved sensitivity or segmented Ge detectors, fast digital encapsulated into a thin Al can using resolving power is due to the new electronics, efficient signal analysis the technology developed for the technique of tracking, which identi- and tracking algorithms, and Euroball cluster and the MINIBALL fies the position and energy of γ-ray improved computational power. In the detectors. The outer contact of each interaction points in the detector seg- following the principles of gamma- crystal is divided into 6 × 6 azimuthal ments. Since most γ rays interact ray tracking will be described. and longitudinal segments to give more than once within the crystal, the 36 electronically independent out- energy-angle relationship of the The Segmented Ge Detector and puts, plus the core signal giving a Compton scattering formula is used to Digital Signal Processing total of 37 signals. The encapsulated track the path of a given γ ray. The The first ingredient of a tracking crystals are provided by the company full γ-ray energy is obtained by sum- spectrometer is the Ge detector itself. Canberra France. ming only the interactions belonging to that particular γ ray. In this way there are no lost scatters into suppression shields and scattered gamma rays between crystals are recovered, thus a much higher overall efficiency can be achieved. A gain by a factor of 6 over Gammasphere/Euroball for a single 1MeV γ ray and about 20 times for 15 MeV γ rays is expected. Other key benefits of a highly segmented Ge array include high energy resolution, high counting rate capability (a factor Figure 3. A spectrum from an AGATA commissioning experiment showing the of ~5 over Gammasphere/Euroball), Coulomb excitation of a 56Fe beam on a 197Au target. The improvement in good position resolution (about 1° resolution with pulse shape analysis and kinematic correction using the DANTE versus 6° for Gammasphere critical detector is clearly apparent. Red is the raw spectrum, blue is corrected for Au for Doppler shift corrections since and black for Fe.

24 Nuclear Physics News, Vol. 20, No. 4, 2010 facilities and methods

The segmentation of the Ge systems need to cope with a large crystal provides the initial position- numbers of channels, over 6,000, and of-interaction information. In order also with very high rates in each to perform γ-ray tracking, the posi- crystal, up to 50 kHz. The principle tions and energies of the γ-ray inter- of the AGATA and GRETA systems actions in the Ge must be even more is to sample these outputs with fast accurately determined from the sig- analogue to digital converters (ADCs) nal waveforms. The position resolu- to preserve the full signal information is a key metric in the detector tion, in as clean an environment as performance. It directly affects the possible, so that accurate energies, efficiency and peak/total of the array, times, and positions can be extracted as well as the effective energy reso- using the signal decomposition algo- lution of the array when used with rithms. Interfaces to enable “easy” the source of radiation travelling electronic coupling of ancillary Figure 5. Side projection of the with high recoil velocity. AGATA detectors to the acquisition system position of the first interaction points and GRETA require state-of-the-art, have been developed. The projects in a GRETINA detector from a purpose-built digital electronics and have adopted slightly different sys- collimated 137Cs source. an associated data acquisition system tem architectures in order to achieve to process the signals from the Ge this and both are now operational. crystals. Signals from the 37 pream- rities. This idealized model of the plifiers of each detector (36 segments Signal Decomposition crystal is not sufficient when applied plus one central contact) are digi- The position and energy of a to real signals, since corrections must tized. From the digitized pulse given interaction in the detector is be made for detector and electronic- shapes processing units derive and found using a procedure called signal response characteristics such as provide additional parameters such decomposition. For each crystal, a preamplifier shaping, relative time as the channel number, the energy, simulation is performed where a unit delays, and integral and differential the raw data samples from the lead- charge is placed at a given point in cross-talk. These corrections are ing edge of the pulse (trace), and a the crystal and the net and transient determined by comparing signal timestamp (in 10-ns steps). The currents induced on each of the 36 traces measured using gamma-ray “data-acquisition” section of the sys- segment contacts, as the charge drifts sources to a simulation, and fitting the tem collates and distributes the toward the electrode, are calculated. required parameters. Both AGATA events to a computer cluster to per- This procedure is carried out on a and GRETA projects have a program form signal decomposition, event grid of points whose spacing reflects of detector scanning in progress to reconstruction, and tracking. These the sensitivity of the detector. Typi- provide the data sets of pulse shapes cally, about 300,000 grid points per for the crystals. crystal are used with spacing varying The signal-decomposition itself from 0.5 to 3 mm. Measured signals can be performed using a variety of are then compared with linear combi- algorithms, but to perform it in real- nations of these simulated signals, as time, count-rate requirements and there are typically multiple interac- computer cost impose stringent limits tion points in a given crystal, with on how much CPU time can be spent the best fit giving the location and per event. The GRETINA decomposi- charge (energy) of the interaction tion code at present uses a two-step points. process that starts with an adaptive The above calculation involves the grid search for one and two interac- geometry of the crystal, the bias volt- tions per segment followed by a Figure 4. The quad-crystal module of age, and a model of the space charge sequential quadratic programming GRETINA. distribution arising from crystal impu- (nonlinear least-squares) fit, which

Vol. 20, No. 4, 2010, Nuclear Physics News 25 facilities and methods

tify interaction points belonging to a pre-processing units, where these given gamma ray. They also identify pulses are analyzed and where, for gamma rays that deposit only partial example, their energies are calculated. energy in the detector and reject them. Each pulse detected on the core con- The main tracking algorithms devel- tact of a detector is time-stamped and oped so far use either back tracking or the Global Trigger System (GTS) is forward tracking techniques. In back informed of its existence. If autho- tracking the algorithm starts from rized by the GTS, the event parame- indentifying the final photoelectric ters are passed on to the Pulse Shape interaction. The forward tracking Analysis processor computer farm algorithms identify cluster of coinci- over high-speed PCI Express links. dent interaction points and fold in the This phase of the project is now probability of Compton scattering. complete and AGATA has commenced Figure 6. Position resolution of These codes are resulting in tracking its first physics operation phase. single interaction determined with efficiencies ranging from ~100% to AGATA is now governed by a new coincidence measurement. The position 50% for γ-ray multiplicities from 1 to MoU that defines the planning, funding, resolution in x and y was found to be 25, respectively. construction, and operation of the Dx = 1.2 mm and Dy = 0.9 mm (RMS), device as it is built up from a 15 detec- respectively. The grid points of the tor system toward the full 4π device. basis signal are indicated. Status and Performance of the AGATA will be sited at different labo- Spectrometers ratories, taking full advantage of the different beams and facilities available, in allows multiple interactions in multi- AGATA order to maximise the breadth of sci- ple segments within a crystal. On the The AGATA collaboration ence that can be addressed. current generation of 2 GHz proces- includes more than 40 institutes in 13 A series of commissioning experi- sors, the GRETINA algorithm countries in Europe that was estab- ments, with sources and stable beams, requires less than 16 ms per CPU core lished to develop and construct a 4π were performed using the AGATA per crystal. tracking spectrometer. The AGATA Demonstrator at Legnaro National It has been shown experimentally collaboration defined that the full Laboratory in Italy. Figure 2 shows that the pulse shape algorithms array will be realized in phases. In the spectrometer currently at Legnaro developed for GRETINA and 2003 a Memorandum of Understand- with five triple cryostats. These AGATA can achieve an average ing (MoU) was signed by the partners experiments ranged from a simple test position resolution of better than 2 for the research and development of an AGATA detector in stand-alone mm (RMS), which is sufficient for phase of the project. This first phase mode through to the coupling of efficient gamma-ray tracking. of the project involved constructing AGATA with the DANTE (a micro an array of 15 detector capsules, channel plate detector) and the Tracking termed the AGATA demonstrator, PRISMA magnetic spectrometer. The tracking process uses the ener- with all the electronics and data These tests were highly successful, gies and positions of the interaction acquisition, pulse shape and tracking enabling many problems to be identi- points, produced by the signal decom- algorithms and associated spectrome- fied and tackled and to optimize the position, to determine the scattering ter infrastructure. In AGATA the performance of the device. As an sequence for a particular γ ray. Algo- crystals are closely packed together in example in June 2009 AGATA was rithms have been developed to track groups of three in a common cryostat coupled to DANTE and gamma rays events based on Compton scattering, provided by the company CTT. In the following the Coulomb excitation of pair-production and photo electric AGATA electronics system the digi- 56Fe were investigated. Figure 3 interactions. For events with multiple tized pulse shape information, gener- shows the improvement to the spec- gamma rays, these algorithms are able ated in units close to the array, is tral resolution made by both using to resolve these gamma rays and iden- transferred via optical cables to kinematic correction from the posi-

26 Nuclear Physics News, Vol. 20, No. 4, 2010 facilities and methods

tion information from DANTE and MSU. The support structure was fabri- completed in 2011. Following the the pulse shape analysis from the cated and installed at the 88-Inch completion, engineering and commis- AGATA crystals. Cyclotron facility at LBNL. The data sioning runs at LBNL will be carried The Legnaro physics campaign acquisition electronics consist of digi- out until December 2011. From started in February 2010 and the tizer and router/trigger modules, which January 2012 to December 2013, it array will remain at Legnaro until sit in VME crates. All the modules will operate 6 months each at NSCL the end of December 2010, utilizing (130 digitizer and 16 router/trigger MSU, HRIBF ORNL, and ATLAS the wide range of stable beams avail- modules) have been produced and ANL with two months for moving able. Subsequent physics campaigns tested and some of them are being used between sites. The current plan is to will be carried out at the GSI facility for detector testing. The computing couple GRETINA with high perfor- in Germany starting in October 2012 system for GRETINA has about 70 mance separators at each of these and the GANIL laboratory in France computer nodes in a cluster for decom- three facilities to perform experiments starting in the spring of 2013/2014 at position and tracking. The installation using stable and radioactive beams. the earliest. At GSI, AGATA will be of these nodes has been completed. used at the exit of the fragment To measure the position resolution Summary and Outlook recoil separator (FRS) to study very of the GRETINA detectors two The advances made in these exotic nuclei produced following related methods have been used. The projects in Ge detector technology, high-energy fragmentation and sec- first method is to place a collimated digital data acquisition (DAQ) sys- ondary Coulomb excitation. At 137Cs source beneath the detector that tems, signal decomposition, and GANIL it will use the wide range of generates a set of events whose first gamma-ray interaction reconstruction radioactive ions from the coupled interaction lies along the line of the have proved that gamma-ray tracking cyclotrons and SPIRAL. During pencil beam. The scatter of first inter- spectrometers can be successfully these first three physics campaigns action points, determined by the deployed. AGATA and GRETINA/ the array will be built up toward a signal decomposition, about this line GRETA will have an enormous impact “1/3” comprising 60 detectors mod- gives a measure of the position reso- on the exploration of nuclear structure ules as the next step to a full imple- lution. Such measurements were car- at the extremes of isospin, proton num- mentation of AGATA. ried out for GRETINA detectors, and ber, angular momentum, excitation Figure 5 gives side projection of the energy, and temperature. These new GRETINA distribution of first-interaction points. devices will constitute a major advance GRETINA is the U.S. project The collimation of the Cs source is in gamma-ray detection sensitivity funded by DOE/NP, which will cover evident. The position resolution per- that will enable the discovery of new π steradian of the total solid angle pendicular to the pencil beam was phenomena, which are only populated with Ge detectors. The major collabo- determined to be 1.5 and 1.7 mm in a tiny fraction of the total reaction rating institutions are LBNL, ANL, (RMS) in horizontal and vertical cross-section or in nuclei that are only MSU, ORNL and Washington Uni- directions, respectively. produced with rates of the order of a versity. GRETINA will have 28 seg- A second characterization is the few per second or less. The unprece- mented, coaxial, Ge crystals with four same as that of a pencil beam measure- dented angular resolution will facili- crystals combined in a single cryostat ment except a second collimator and tate high-resolution spectroscopy with to form a quad-crystal module. Ge detector is placed at 90° to the point fast and ultrafast fragmentation beams GRETINA is the first stage of the full of interest in the detector. By setting a giving access to the detailed structure GRETA spectrometer, which will coincidence condition between the of the most exotic nuclei that can be have 30 quad-crystal modules to detectors and setting appropriate reached. Finally, the capability to cover the full solid angle. energy gates in each, single interaction operate at much higher event rates Currently, six detectors modules points at a given position in a segment will allow the array to be operated for have been received. Figure 4 shows can be selected. The results of such a reactions with intense gamma-ray one of the modules. The extensive test- measurement are shown in Figure 6. backgrounds, which will be essential ing and characterization of the detec- The construction of GRETINA for the study of, for example, transu- tors is being carried out at LBNL and started in 2005 and is scheduled to be ranic nuclei.

Vol. 20, No. 4, 2010, Nuclear Physics News 27 facilities and methods

The instrumentation and technical References advances driven by this work, and the 1. J. Simpson, Z. Phys. A358 (1997) 139. knowledge gained by those involved, is 2. M. A. Delaplanque and R. M. Dia- important in a wide range of applica- mond (Eds.), Gammasphere Proposal tions. These advances have potential (1987), Preprint LBNL-5202. 3. J. Eberth et al., Prog. Nucl. Part. Phys. impact in areas such as medical imaging 46 (2001) 389. in single photon emission computed 4. D. Habs et al., Prog. Nucl. Part. Phys. tomography (SPECT) and positron 38 (1997) 111. emission tomography (PET) systems, 5. J. Simpson et al., APH N.S. Heavy Ion homeland security, and environmental Phys. 11 (2000) 159. monitoring. 6. F. Azaiez, Nucl. Phys. A654 (1999) The realization of AGATA and 1003c. 7. W. F. Mueller et al., Nucl. Instr. and GRETINA is the result of a tremen- I-YANG LEE Meth. A466 (2001) 492. dous amount of hard work by many 8. S. Shimoura, Nucl. Instr. and Meth. A Lawrence Berkeley National people and laboratories and the sup- 525 (2004) 188. Laboratory, Berkeley, CA, USA port of many funding agencies. We 9. M. A. Deleplanque et al., Nucl. Instr. take this opportunity to thank all those and Meth. A430 (1999) 292. involved and wish everyone success 10. I. Y. Lee, M. A. Deleplanque, and K. in their scientific endeavors using Vetter, Rep. Prog. Phys. 66 (2003) 1095. these beautiful instruments. 11. J. Simpson, Acta Physica Pononica Further information about B36 (2005) 1383. AGATA and GRETA can be found at 12. J. Gerl, Acta Physica Polonica B34 Refs. [15] and [16], respectively. (2003) 2481. 13. J. Simpson and R. Kruecken, Nucl. Phys. News Intl. 13 (2003) 15. Acknowledgement 14. J. Eberth and J. Simpson, Prog. Part. The work done at LBNL is sup- Nucl. Phys. 60 (2008) 283. JOHN SIMPSON ported by US DOE under Contract 15. http://www.gsi.de/agata/ STFC Daresbury Laboratory, No. DE-ACO2-O5CH11231. 16. http://grfs1.lbl.gov/ Daresbury, Warrington, UK

28 Nuclear Physics News, Vol. 20, No. 4, 2010 facilities and methods

The WASA Facility at COSY

The WASA (Wide Angle Shower mechanisms in hadronic systems as place detectors very close to the Apparatus) facility is a 4π detector sys- well as hadron spectroscopy. The aim is interaction point, at the expense of tem for charged and neutral particles to investigate properties of quantum acceptance or resolution of the vertex that has been designed to study produc- chromodynamics (QCD) in the non- reconstruction. The unique pellet tar- tion and decay of light mesons. After perturbative regime, where confinement get concept proposed by Kullander successful operation at CELSIUS the and chiral symmetry breaking are the [3] avoids to a large extent this trade- facility has started data taking as fixed distinctive phenomena. For instance, in off: Using a vibrating nozzle at typi- target internal experiment at the COoler decays of light mesons and dedicated cal frequencies around 70 kHz, a jet SYnchrotron and storage ring COSY meson production experiments isospin of liquid hydrogen or deuterium near [1] at Forschungszentrum Jülich in symmetry can be subjected to direct triple point conditions is broken up 2007. COSY delivers beams of polar- measurements, and fundamental C, P, into droplets with typical diameters ized and unpolarized protons and deu- and T symmetries can be probed in high of about 35 μm in the case of hydro- terons in the momentum range between statistics studies of meson decays or gen (Figure 2). The droplets freeze 0.3 and 3.7 GeV/c. In collisions with a rare decay searches. The physics case by partial evaporation in a droplet hydrogen or deuterium target, mesons for WASA at COSY is described in chamber and form a stream of small with masses up to the φ meson can be more detail in Ref. [2]. frozen microspheres. After collima- produced. The WASA detector setup tion, the pellets move at velocities (Figure 1) comprises a forward part to Pellet Target in the order of 100 m/s and with an measure charged target-recoil particles Typically, in experiments using angular spread of about 1 mrad. and scattered projectiles, a central part internal windowless gaseous targets They are directed through a thin 2 m to measure meson decay products, and high gas loads arise close to the long pipe into the scattering cham- a pellet target. interaction region. Thus, a reason- ber and are collected further down Experiments with the WASA detec- able precision and life-time of the in a pellet beam dump. Average dis- tor at COSY focus on studies of circulating beam requires high tances between consecutive pellets symmetries and symmetry breaking pumping capacity, and prevents to as short as 9–20 mm have been

Figure 1. Schematic view of the WASA detector setup. The interaction region defined by the COSY beam and the pellet target is enclosed by the central detector. The forward direction is covered by a straw tracker and plastic scintillator layers.

Vol. 20, No. 4, 2010, Nuclear Physics News 29 facilities and methods

Another target [4] is presently being developed. This detector will also developed for the PANDA experi- serve as a prototype for the PANDA ment [5] at the future FAIR facility. experiment. The central part of the detector Detector around the interaction point is designed The forward part of the detector— to detect meson decay products (i.e., four proportional chamber layers photons, electrons, and charged consisting of drift tubes (straws) and pions): 1,012 sodium-doped CsI scin- 13 planes of plastic scintillators—is tillating crystals of about 16 radiation used to measure scattered projectiles lengths form the electromagnetic calo- and charged recoil particles like pro- rimeter, covering 96% of the full solid tons, deuterons, and He nuclei. Parti- angle. The energy of electromagnetic cle identification is based on the ΔE showers from photons, electrons, and – E method using the energy deposit positrons can be measured with a res- E in the Range Hosdoscope layers olution of 5%/√E[GeV]. The calorim- (Figure 3). Particles are stopped in eter encloses a thin (0.18 radiation the scintillator material up to kinetic lengths) superconducting solenoid energies ranging from 350 MeV for that provides an axial magnetic field protons to 1,000 MeV for α particles, up to 1.3 T. With few percent accu- and the energy can be reconstructed racy, charged particle momenta can be with a precision of ≈3%. In addition, determined from the track curvature the particle time-of-flight can be measured in the cylindrical straw used, especially at higher energies, chamber placed inside the solenoid, where the accuracy of the ΔE – E and reaction vertices can be recon- method deteriorates. To further structed. To minimize the material improve the energy resolution in this budget, the beam pipe inside the straw regime, an imaging Cherenkov chamber is made of 1.2 mm thin counter using the Detection of Inter- beryllium. The chamber is surrounded Figure 2. Stroboscopic view of the nally Reflected Cherenkov light by a barrel arrangement of plastic scin- liquid hydrogen jet being broken up (DIRC) principle is presently being tillators, consisting of a cylindrical part into droplets in the droplet formation chamber before vacuum injection and collimation. The vibrating nozzle is seen on top. 150

120

reached. The pellet target provides a 90 point-like well-defined interaction d region and the space for an almost 60

4π angular coverage. Effective E (layer 1) [a.u.] p Δ target thicknesses of >1015 cm–2 and— 30 with available beam intensities at π 32 0 COSY —an average luminosity of 10 0 30 60 90 120 150 180 –2 –1 cm s can be reached at a minimum ΔE (layer 2) [a.u.] gas load to the storage ring. At the moment, the WASA pellet target is Figure 3. Identification of pions, protons, and deuterons from proton-proton the only pellet target in operation at scattering data at 400 MeV kinetic beam energy using the first two layers of the an internal storage ring experiment. Range Hodoscope (Figure 1) in the forward detector.

30 Nuclear Physics News, Vol. 20, No. 4, 2010 facilities and methods

and two end-caps, placed inside the number, the electronic dead-time of m(η)

] 0.8 solenoid. Charged particle identification the system amounts to 20 μs per event 2

in the central detector is achieved from and event and data rates of 7 kHz and [GeV/c

γ) 0.6 combining reconstructed momenta 80 MBytes/s are written to disk. m(η) with either the barrel energy loss 0.4 information or the energy deposit in Experimental Technique invariant mass (6 the calorimeter (Figure 4). The scintil- For a given physics case, the 0.2 lator barrel can also be used as a veto WASA experimental setup allows 0 0.2 0.4 0.6 missing mass (pp)[GeV/c2] signal on charged tracks for photon both charged and neutral final states identification. to be measured with high accep- Figure 5. η meson tagging via the 6γ Prior to the installation of WASA tance at the same time, which invariant mass from the decay η → at COSY the data acquisition system significantly reduces systematical 3π0 → 6γ and the missing mass with has been completely replaced using uncertainties. In typical decay stud- respect to the proton-proton system in state-of-the-art FPGA technologies ies, mesons are predominantly pro- pp → ppη data at a kinetic beam for event and buffer management duced in the tagging reactions pp → energy of 1400 MeV (linear scale). combined with fast communication ppX and pd → 3HeX, where paths to achieve low system latencies X denotes a neutral meson. The and highest possible event rates [6]. production cross-sections in proton- For the digitizing layer TDC and proton induced reactions are generally COSY is achieved by an electron QDC boards have been developed. higher, and allow for rare decay cooler for the low-momentum range The QDCs sample the analog signals searches. On the other hand, the and a stochastic cooling system at by FlashADCs prior to charge inte- 3HeX final state is easier to tag by high energies. However, with a high gration, and a fast feature extraction the energy loss of 3He ions in the areal density pellet target the energy capability allows to include particle forward detector and has lower loss can not be compensated by energy information at the trigger background from multi-pion pro- cooling techniques alone. Instead, level. As a typical performance duction. The meson X is identified this is achieved using a broadband by combining the missing four- barrier bucket cavity, as shown in momentum with respect to the pp Figure 6, in combination with the system or the 3He detected in the stochastic cooling system to further forward detector with the invariant reduce the beam momentum spread mass of the mesonic decay products [7]. Due to a reduced peak bunch reconstructed from the central intensity and a smaller time gap detector information (Figure 5). between consecutive bunches com- The flexible trigger system allows pared to a conventional RF cavity data taking with a minimum bias on sinusoidal voltage, the barrier the decay system. Several or even all bucket technique allows to obtain a decay modes, charged and neutral, of more DC-like beam, that can be a given meson can be tagged using the efficiently cooled in momentum. forward detector trigger conditions on Experimentally, this situation is the pp or 3He system. advantageous, since the peak-to- average luminosity is equalized and Figure 4. Monte Carlo simulation the duty cycle is increased. showing the separation of pions, Accelerator Operation The effective target thickness in electrons, and positrons in the WASA The interaction of the coasting Figure 6 corresponds to ≈3·1015 central detector from the energy ion beam with an internal target atoms/cm2, and has been deduced (E) measurement in the calorimeter induces an energy loss of the beam from the shift of the beam revolution and the reconstructed particle and an increase in relative momen- frequency due to the energy loss momentum. tum spread. Phase space cooling at of the beam particles (case (b) in

Vol. 20, No. 4, 2010, Nuclear Physics News 31 facilities and methods

References 1. R. A. Maier, Nucl. Phys. News 7N4 (1997) 5. 2. H.-H. Adam et al., Proposal for the Wide Angle Shower Apparatus (WASA) at COSY-Jülich— “WASA at COSY,” arXiv: nucl-ex/0411038. 3. S. Kullander, CELSIUS information day 1984-10-01, unpublished; B. Trostell, Nucl. Instr. Meth. A 362 (1995) 41. 4. A. V. Boukharov et al., Phys. Rev. Lett. 100 (2008) 174505. 5. W. Erni et al. (PANDA Collabora- tion), Physics Performance Report for PANDA: Strong Interaction Studies with Antiprotons, arXiv: 0903.3905 [hep-ex]. 6. H. Kleines et al., IEEE Trans. Nucl. Sci. 55 (2008) 261. 7. H. Stockhorst et al., 1st Int. Particle Accelerator Conference (IPAC’10), Figure 6. Schottky noise spectra of a COSY proton beam measured at the Kyoto, Japan (2010), http://accel- 1000th harmonic for (a) the initial distribution, (b) after 180 s only with pellet conf.web.cern.ch/AccelConf/IPAC10 target, (c) with pellet target and cooling, (d) with pellet target, cooling, and barrier bucket. Since the working point of the machine was chosen above gamma-transition energy loss results in a shift toward higher revolution frequencies.

Figure 6). Similar target densities are quality proton and deuteron beams expected for a pellet target at the available at COSY. It is operated and PANDA experiment at the High- maintained by a collaboration pres- Energy Storage Ring HESR. Thus, ently consisting of more than 170 the operation of a highly dense scientists from 35 institutions in internal pellet target with a phase 8 countries. Exploiting high luminosi- space cooled proton beam at COSY is ties and large hadronic production a one-of-a-kind testing ground to be cross-sections gives the facility a able to provide antiproton beams with huge potential for hadron physics in significantly reduced momentum the light quark sector in the forthcom- spread for PANDA at HESR in future. ing years. Its physics results should deepen our understanding of the Conclusion strong interaction at small and moder- WASA-at-COSY combines a ate energy scales, which are of deci- unique target concept and a close to sive relevance to the question how MAGNUS WOLKE 4π detector setup with the high nature makes hadrons. Uppsala University

32 Nuclear Physics News, Vol. 20, No. 4, 2010 meeting reports

11th Symposium on Nuclei in the Cosmos (NIC XI)

Nuclei in the Cosmos is a series In addition to 33 invited speakers, heavy r-process elements. The differ- of biannual conferences that bring the organization received more than ent observational results presented at together nuclear experimentalists, 300 contributions. 55 of these contri- the meeting confirmed the different nuclear theorists, astronomers, theo- butions were selected by the Interna- astrophysical origin for the light and retical astrophysicists, cosmochem- tional Advisory Committee for oral heavy r-process elements. Current ists, and others interested in the presentations and the rest were pre- state-of-the-art core-collapse super- scientific questions at the interface of sented as posters. The oral program novae models can account for the nuclear physics and astrophysics. consisted of 18 sessions addressing observations of light r-process ele- The 11th conference of this series the following topics: the Big Bang, ments; however, heavy r-process (NIC XI) held on 19–23 July 2010 in the first stars, chemical evolution and elements are not produced in these Heidelberg, Germany, was attended stars, grains and gamma-ray observa- models. The first three-dimensional by 297 participants (207 from outside tions, core-collapse supernovae, the s- hydrodynamical models of mixing in Germany representing 36 countries), process, X-ray bursts, explosive nucleo- Novae were presented at the meet- among them 120 students. It was synthesis: νp-process, ν-process and ing. The largevariety of X-ray bursts jointly organized in the scientific p-process, the p-process and exotic recently observed can be related to partnership between the University of nuclei, the r-process, and future facili- the burning of different fuels and to Heidelberg, the Max-Planck-Institute ties. Following the tradition of previ- their previous burning history. for Nuclear Physics (Heidelberg), the ous meetings, each session started Similarly, the large variety of type Ia GSI Helmholtzzentrum für Schweri- with a review by an expert in the field supernovae suggests the existence of onenforschung (Darmstadt), the Uni- and then the major recent advances several progenitor channels includ- versities of Basel, Darmstadt, Frankfurt, were reported in contributed talks. ing mergers of two white dwarfs. Giessen and Mainz, the Frankfurt There were two poster dinner sessions Astrophysical observations of neu- Institute for Advanced Studies, the in the late afternoon of Tuesday and tron stars are providing new informa- Max-Planck-Institute for Chemistry Thursday that were massively attended tion on their masses and radii, that (Mainz), and the Cluster of Excel- by the participants. The best three have shed new light on the pressure- lence on the “Origin and Structure of posters received a prize. density relation of extremely dense the Universe” (Munich). The meeting From the large amount of scien- matter, implying that the neutron star was sponsored by the Max-Planck- tific topics discussed during the maximum mass is possibly two solar Institute for Nuclear Physics, Deut- conference, we would like to high- masses. Thanks to recent progress in sche Forschungsgemeinschaft, the light a few. Analyses of dwarf galax- nuclear mass measurements most of Helmholtz International Center for ies of the Milky Way system show a the masses of neutron deficient FAIR, the GSI Helmholtzzentrum für striking similarity between their nuclei that participate in explosive Schwerionenforschung, the Interna- abundance patterns and those seen in nucleosynthesis scenarios like the rp- tional Union of Pure and Applied metal-poor halo stars. This can pro- process or the νp-process have been Physics, the Cluster of Excellence on vide important clues for the forma- experimentally measured. The situa- the “Origin and Structure of the Uni- tion and evolution of our galaxy and tion is more demanding for neutron- verse” Munich, and the University of its early chemical evolution, particu- rich nuclei. Nevertheless, important Basel. The participation of more than larly of r-process elements. As a progress was reported for this nuclei 60 participants was financially sup- matter of fact, chemical evolution including the first measurement of ported, and a reduced conference fee models that consider a hierarchical beta-decay lifetimes for nuclei for students was provided. The meet- formation of the Milky Way show approaching the N = 126 r-process ing was surrounded by three satellite that neutron star mergers could be waiting point. Recent progress in workshops and a Wilhelm and Else the major source of heavy r-process extended density functional Heraeus Summer School on Nuclear elements. These may solve the long approaches for the description of Astrophysics in the Cosmos. standing problem of the origin of ground-state correlations in nuclei

Vol. 20, No. 4, 2010, Nuclear Physics News 33 meeting reports

will allow for systematic improve- More details on the 11th Sympo- KLAUS BLAUM ments in the precision of the nuclear sium on Nuclei in the Cosmos can be Max-Planck-Institute für Kernphysik, physics input necessary for astro- found on the conference website: Heidelberg physical applications. Particular http://www.lsw.uni-heidelberg.de/nic attention was given on the last day 2010/index.phtml NORBERT CHRISTLIEB to the opportunities offered by the The next NIC conference will be Ruprecht-Karls-Universität future facilities for radioactive held in the (northern hemisphere) sum- Heidelberg beams, for probing stellar reaction mer of 2012 in Cairns, Australia. We processes and for surveys for high- wish the organizers of NIC XII a fruitful GABRIEL MARTÍNEZ-PINEDO resolution spectroscopy of metal- and successful symposium with as GSI Helmholtzzentrum für poor stars. much Sun as we had in Heidelberg. Schwerionenforschung, Darmstadt

The Second Edition of the State of the Art in Nuclear Cluster Physics Workshop

A great deal of research work has The second workshop SOTANCP clusters in nuclei in an informal been performed in the field of alpha that took place 25–28 May 2010 at atmosphere favorable to discussions. clustering since the pioneering dis- the Université Libre de Bruxelles The purpose of SOTANCP2 was to covery of molecular resonances in (Brussels, Belgium) was organized by promote the exchange of ideas and the excitation functions for 12C+12C P. Descouvemont, M. Dufour and J.-M. discuss new developments in Cluster- scattering. The aim of the series of Sparenberg. The first workshop was ing Phenomena in Nuclear Physics. State of the Art in Nuclear Cluster held in Strasbourg, France, in 2008 Applications in Condensed Matter Physics (SOTANCP) Workshops is (Nuclear Physics News, Vol. 18, No. 3, and Nuclear Astrophysics were also to further discuss the many facets of p. 38). This second meeting was dedi- presented. The various aspects of the clustering in nuclear physics facing cated to Daniel Baye (Figure 1) on the main topics of SOTANCP2 were in different directions the great chal- occasion of his 65th birthday. As in divided into eight sections, each high- lenges and opportunities in the years Strasbourg, it brought together differ- lighting an area where open questions ahead. ent groups involved in the study of have emerged over recent years:

34 Nuclear Physics News, Vol. 20, No. 4, 2010 meeting reports

• Cluster Structure of Stable and talks of 25 minutes were presented by be found at http://pntpm4.ulb.ac.be/ Unstable Nuclei, including Haloes distinguished colleagues in their sotancp2. The Proceedings, in the • Alpha Clustering and Nuclear respective area of expertise as part of form of peer-reviewed papers of all Molecules the 16 plenary sessions. As the orga- the orally presented talks, will be pub- • Clusters in Nuclear Astrophysics nizers wished to make possible to lished in a forthcoming issue of the • Clustering Aspects of Nuclear have all submitted contributions pre- International Journal of Modern Reactions sented orally, 61 shorter talks were Physics E. • Alpha Condensates and Analogy also given during the four days of the Owing to the interest shown by with Condensed Matter Approaches meeting. the community and the potential for • Cluster Radioactivity The most recent developments of future research in clustering in • Clusters in Hypernuclei clustering in nuclear structure were nuclei, the members of the Interna- • Cluster in Superheavy Nuclei presented primarily for light stable tional Advisory Committee have and unstable nuclei (Y. Suzuki, M. agreed to consider SOTANCP as a The Workshop attracted 88 partici- Freer, M. Milin, T. Neff, K. Kato, N. series of meetings to complement the pants from some 21 different coun- Timofeyuk, R. Raabe). Alpha-particle traditional CLUSTER Conferences tries of all continents (Africa, Asia, condensation and the search for an (Nuclear Physics News, Vol. 18, Australia, Europe, North America, equivalent Hoyle state in nuclei No. 1, p. 25). Since the next Cluster and South America). It should be heavier than 12C were among the conference, organized by our Hun- noticed that a large number of our highlights that were most actively dis- garian colleagues, will take place in Japanese colleagues travelled to cussed (T. Kawabata, Y. Funaki, N. 2012 in Debrecen, it has been Europe to attend the meeting. This Itagaki). Various microscopic cluster- decided to have the next SOTANCP reflects a long-standing collaboration model approaches (S. Aoyama, E. workshop in four years. Japan being with Japanese scientists in cluster Hiyama, Y. Fujiwara) to the under- one of the most active countries in physics. The formats of the sessions standing of hypernuclei and four Nuclear Cluster Physics, it was natu- were such that a sufficient amount of nucleon scattering were also pre- ral to have SOTANCP3 organized in time was available for both discus- sented. As usual, D. Baye displayed the country of the rising sun. We sions and questions. Eighteen invited his excellent pedagogical skills by look forward to the new and exciting proposing a very nice overview of the works that will be presented at cluster-model description of colli- the third SOTANCP workshop in sions. Very recent results were also Yokohama in 2014. reported on collisions for incident energies ranging from the Coulomb CHRISTIAN BECK barrier (P. Figuera, M. Rodriguez- IPHC/DRS et Université de Gallardo) to the Fermi energy (J. Strasbourg, France Natowitz) up to relativistic energies (P. Zarubin). The study of clustering PIERRE DESCOUVEMONT effects in reaction mechanisms has Université Libre de Bruxelles, gained a renewed interest with the Belgique availability of radioactive ion beam facilities. MARIANNE DUFOUR The Workshop was sponsored by IPHC/DRS et Université de both the Fonds de la Recherche Strasbourg, France Scientifique (F.R.S.-FNRS) and the Université Libre de Bruxelles (ULB). JEAN-MARC SPARENBERG Details of the Workshop program Université Libre de Bruxelles, Figure 1. Daniel Baye. (including the slides of the talks) may Belgique

Vol. 20, No. 4, 2010, Nuclear Physics News 35 meeting reports

First Azarquiel School of Astronomy

The first Azarquiel school of astronomy—“a bridge between east and west”—took place on 4–11 July 2010 in Granada (Spain), near the Alhambra (Figure 1). About 40 students and young scientists from 20 different countries in Europe (such as Denmark, Italy, Romania, and the United Kingdom) and in the Middle East/Arabic world (such as Palestine, Iran, Turkey, and Israel) participated in the school, each group in about equal numbers, also in the number of females and males. There were 4 lecture days and 2 days devoted to a visit of the observatory of Calar Alto, the Alhambra, and other historic places. The lectures addressed issues such as (i) the history of Arabic astronomy, Figure 1. The Alhambra. (ii) telescopes, instruments, and fore- front astronomy, (iii) stellar systems: a hierarchy of ages, sizes, and processes, asked questions during and after a The school was supported by the and (iv) physics and stars. Late in the given lecture as well as in the free University of Granada, the Spanish evenings several open conferences were times. They interacted also inten- Plan for the Alliance of Civilizations, organized: (i) Andalusian astronomy in sively among themselves and new the Spanish Ministry of Science and the 11th century: Azarquiel and his friendships and collaborations were Innovation, the Euroarab Foundation, school, (ii) Islamic science and the mak- born. In an open “round-table” discus- and the Spanish Astronomical Soci- ing of the European renaissance, (iii) sion near the end of the school they ety; cultures and scientific visits were high energy astrophysics from space, expressed their excitement about the funded by the Astronomical Observa- and (iv) the history of the elements. In school and that it should be repeated tory of Calar Alto, the Catedra Al- addition, there were short presentations in the near future. They suggested fur- Babtain, and the “Legado Andalusi.” of the young participants. Although thermore the formation of working For more information, visit http:// more than 90 students/scientists had groups dealing with specific astro- www.azarquiel-school.org applied for the school, only 40 partici- nomical or astrophysical issues. It was pants could be supported due to limited also discussed whether the school INMA DOMÍNGUEZ available funding. should move from time to time to AND CARLOS ABIA It was a very lively school since other countries/universities such as University of Granada the young participants frequently Lebanon and Turkey. Local organizers

36 Nuclear Physics News, Vol. 20, No. 4, 2010 news and views

Elvira Moya de Guerra Receives the Gold Medal of the Spanish Royal Physical Society

On 6 July the annual prizes of the four years. She has served, and con- from deformed nuclei, momentum Spanish Royal Physical Society tinues to serve, in many scientific distributions and spectroscopic fac- (RSEF) were awarded. The ceremony committees. In particular she was a tors or spin-isospin excitations. At took place at the Palace Marqués de member of the Board of Directors of present she is mainly involved in scal- Salamanca, in Madrid, the headquar- ECT* (Trento) and of the Editorial ing and parity violation in electron ters of the BBVA Bank Foundation Board of Nuclear Physics News. After scattering, as well as in double-beta that sponsors the RSEF prizes. The completing her Ph.D. in Physics at the decay processes and their Gamow- main prize, “Medalla RSEF- University of Zaragoza she worked Teller branches. In her long and fruit- Fundación BBVA,” was awarded to for five years at the Center for Theo- ful career at the Scientific National our colleague Elvira Moya de Guerra retical Physics of MIT (Cambridge, Council (CSIC), in Spain, she trained (maiden name, Elvira Moya Val- MA, USA) as a Postdoc and as a several generations of theorists and gañón) for “her prestige and leader- Senior Research Scientist. She was strongly supported the development ship in the national and international the first woman physicist in Spain to of Experimental Nuclear Physics. scientific community in Nuclear have access “por oposición” to a Full Recently she moved back to the Uni- Physics and related areas, as well as Professor position, in 1982, and one versity (to Universidad Complutense for her continuous collaboration with of the first Spanish physicists to be de Madrid), motivated by her strong RSEF.” Professor Moya de Guerra named Fellow of the American Physi- concern for teaching Nuclear Physics was the first Spanish representative in cal Society (APS). to undergraduate students. NuPECC, where she served for ten She has contributed to a variety of The Spanish Royal Physical years since 1989. In that period she problems in Theoretical Nuclear Phys- Society has its origins in the former created the division of Nuclear Phys- ics, from microscopic theories of col- Spanish Society for Physics and ics of RSEF, which she chaired for lective modes to electron scattering Chemistry, born in 1903. In 1979 this Society was divided in two, one for Chemistry and one for Physics, but at an earlier stage, in 1928, His Majesty the King Alfonso XIII honoured the Society with the Royal title. The gold medal prize in Physics was awarded for the first time in 1958 to the late Professor Joaquín Catalá de Alemany, a famous atomic spectroscopist trained in the United Kingdom in the early ‘30s who suffered the demolishing consequences of the Spanish Civil War. The medal was established in 1958 to acknowledge the research activity, the scientific career, and the contribution to the RSEF of the awarded member.

J.M. GOMEZ AND J.M. UDIAS Facultad deCiencias Fiscas, University Complutense de Madrid

Vol. 20, No. 4, 2010, Nuclear Physics News 37 obituary

Wladyslaw J. Swiatecki, 1926–2009

recognize the important role of shell effects and the Droplet Model developments that he led constitute major conceptual advances. The associated finite-range nuclear Thomas-Fermi model, with shell effects incorporated by means of the so-called macroscopic–microscopic method, has provided the field with a consistent and remarkably accurate tool for calculating diverse nuclear properties, such as bind- ings, deformations, and fission barriers. He contributed significantly to The distinguished theoretical (1956–57), before taking up a per- the understanding of damped physicist Wladyslaw (Wladek) Swi- manent position at the Radiation Lab- nuclear collisions. In particular, he atecki passed away at his home in oratory in Berkeley, California, now introduced the nuclear proximity Berkeley, California, last autumn. He the Lawrence Berkeley National Lab- force and elucidated the mechanism was 83 years old. oratory (LBNL). Although he for- of one-body damping that opened Wladek was born in 1926 and mally retired in 1991, Wladek up entirely new ways of analyzing spent his early years in Lublin, remained fully active at LBNL and nuclear dissipative processes. The Poland. Following the invasion of he was engaged in his work until the associated insights into nuclear Poland in 1939, his family escaped end of his life. dynamics led to a practically very to England where Wladek com- Wladek’s contributions to nuclear useful model for calculating the pleted his education; after receiving physics have won worldwide recogni- optimal bombarding energy for fus- Bachelor of Science degrees in tion. He has been on the leading edge ing two heavy nuclei. In his later Physics (1945) and Mathematics of studies in fission theory, nuclear years, Wladek worked closely with (1946) at the Imperial College, he mass formulae, superheavy element the Heavy Element Group in Berke- studied under Rudolph Peierls at production, and strongly damped col- ley, applying his model and insights Birmingham University and lisions. Wladek produced a landmark to the planning and analysis of received his Ph.D. in Physics in series of papers in which a unified experiments. 1950 with a thesis entitled “The approach of unprecedented precision An outgrowth of the work on Surface Energy of Nuclei,” a recur- was applied to the elucidation of bar- nuclear dissipation was Wladek’s ring topic throughout his research rier properties for nuclei throughout keen interest in chaos theory, as he career. the periodic table. His work on super- sought to illuminate the key role Subsequently, Wladek spent a heavy elements was definitive in played by symmetries for the charac- number of years in Scandinavia, establishing the physical reasons for ter of the nuclear shape dynamics. first at the Institute of Theoretical such possible islands of stability Wladek also contributed actively to Physics (now the Niels Bohr Insti- beyond the heaviest elements then the developments of the fundamental tute) in Copenhagen (1950–53), known. concepts in the field of high-energy then at the Department of Mathe- Probably Wladek’s work in the nuclear collisions that was emerging matical Physics and the Gustav Werner area of nuclear mass formulae has with the advent of the Bevalac in the Institute in Uppsala (1953–56), and found the widest application. seventies. In particular, he formu- finally at the University of Aarhus Wladek was among the first to lated the concepts of “participants”

38 Nuclear Physics News, Vol. 20, No. 4, 2010 obituary

and “spectators” and developed the of their own. Wladek was elected a scientific contributions and his associated abrasion–ablation model member of the Royal Danish inspiring participation in any dis- around which much of the subsequent Academy of Sciences and Letters in cussion, but also as a warm, kind, modeling was done. 1973. He maintained active collabora- and caring person, full of enthusi- Wladek’s major scientific achieve- tions with nuclear physicists in his asm, charm, and humor. He lived a ments are associated with advancing native country, Poland, where he was life filled with diverse activities and our understanding of macroscopic a member of the Academy of Arts had a profound influence on those nuclear properties, static as well as and Sciences; he was awarded the of us who were fortunate enough to dynamic. In this he has been the stan- Smoluchowski Medal of the Polish know him. dard bearer for generations and he has Physical Society and he received an served as a mentor for numerous honorary degree from the Jagiellonian JORGEN RANDRUP AND BILLMYERS, younger colleagues, including a num- University in Crakow in 2000. Retired ber of graduate students who have Wladek will be remembered Lawrence Berkeley National developed successful research careers not only for his many outstanding Laboratory

News from EPS/NPB

IBA-Europhysics Prize 2011 for Applied Nuclear Science and Nuclear Methods in Medicine Call for Nominations

The board of the EPS Nuclear a brief curriculum vitae of the nomi- University Avenue, Physics Division calls for nominations nee(s) and a list of major publications. Glasgow G12 8QQ UK for the 2011 IBA-Europhysics prize Letters of support from authorities in E-mail: douglas.macgregor@glasgow. sponsored by Ion Beam Applications, the field that outline the importance of ac.uk Belgium. The award will be made to the work would also be helpful. one or several individuals for outstand- Nominations will be treated in For nomination forms and more ing contributions to Applied Nuclear confidence and, although they will be detailed information visit the EPS Science and Nuclear Methods and acknowledged, there will be no fur- Nuclear Physics Division website: Nuclear Researches in Medicine. ther communication. Nominations http://nuclear.epsdivisions.org/ The board would welcome propos- should be sent to: The deadline for the submission of als which represent the breadth and the proposals is January 15, 2011. strength of Applied Nuclear Science and Chair IBA Prize Selection Committee Nuclear Methods in Medicine in Europe. Dr. I.J.D. MacGregor, DOUGLAS MACGREGOR Nominations, on a prize nomina- School of Physics & Astronomy, Univgersity of Glasgow, tion form, should be accompanied by University of Glasgow, Glasgow, UK

Vol. 20, No. 4, 2010, Nuclear Physics News 39 calendar

December 8–10 April 3–8 June 12–18 CERN, Geneva, Switzerland. Eilat, Israel. Nuclear Physics in Crete, Greece. 11th International ISOLDE Physics Workshop and Users Astrophysics 5 Conference on Applications of Meeting http://www.weizmann.ac.il/ Nuclear Techniques http://indico.cern.ch/conferenceDisplay. conferences/NPAS/ http://www.crete11.org/ py?confId=107080 April 27–May 1 August 8–12 December 14–16 Vancouver, Canada. 10th Interna- Manchester, UK. Rutherford Catania, Italy. Nuclear Physics tional Conference on Low Energy Centennial Conference on Nuclear with Modern Magnetic Spectrometers Antiproton Physics (LEAP 2011) Physics http://agenda.infn.it/conferenceDisplay. http://leap2011.triumf.ca/ http://rutherford.iopconfs.org/ py?confId=2935 May 2–6 September 5–9 December 15–20 Saint Malo, France. FUSION11 Vienna, Austria. International Honululu, Hawaii, USA. PACI- http://fusionl1.ganil.tr/ Conference on Exotic Atoms and FICHEM 2010 Related Topics - EXA2011 http://www.pacifichem.org/ May 17–20 http://www.oeaw.ac.at/smi/research/ Newport News, Virginia, USA. talks-events/exotic-atoms/exa-11/ 2011 The 18th International Workshop on the Physics of Excited Nucleons September 11–18 January 8–9 (NSTAR 2011) Piaski, Poland. XXXII Mazurian Piscataway, NJ, USA. Workshop http://conferences.jlab.org/nstar2011/ Lakes Conference on Physics on Advances in Nuclear Radiation index.html http://www.mazurian.fuw.edu.pl/ Detectors and Technologies http://sawg.physics.fsu.edu/Rutgers/ May 31–June 3 October 11–15 Rutgers_Workshop/Home.html Leuven, Belgium. Advances in Kyoto, Japan. Yukawa Interna- Radioactive Isotope Science (ARIS – tional Seminar “Frontier Issues in January 23–29 2011) Physics of Exotic Nuclei” (YKIS2011) Bormio, Italy. XLIX International http://iks32.fys.kuleuven.be/aris/ http://www2.yukawa.kyoto-u.ac.jp/ Winter Meeting on Nuclear Physics ~ykis2011/ykis/index.html http://www.bormiomeeting.com/ June 6–10 Protvino, Russia. PANDA Collab- November 23–28 January 24–27 oration Meeting Hanoi, Vietnam. International Caen, France. SPIRAL2 Week http://www-panda.gsi.de/auto/ Symposium on Physics of Unstable http://pro.ganil-spiral2.eu/events/sp2/ home.htm Nuclei 2011 (ISPUN11) spiral2week-2011 http://www.inst.gov.vn/ispun11/ June 6–10 February 21–23 Bordeaux, France. Fourth Interna- 2012 Valencia, Spain. EURISOL User tional Conference on Proton-emitting Group Topical Meeting Nuclei PROCON2011 September 17–21 http://ific.uv.es/~eug-valencia/ http://www.cenbg.in2p3.fr/ Bucharest, Romania. European PROCON2011/ Nuclear Physics Conference EuNP February 25–27 C2012 Hilton Head Island, South Carolina, June 12–17 http://www.ifin.ro/eunpc2012/ USA. Waltzing to the Nuclear Limits New London, NH, USA. Gordon http://www.phy.anl.gov/nuclearlimits Research Conference on Nuclear 2011/ Chemistry March 28–April 1 http://www.grc.org/ New York, USA. Particle Acceler- programs.aspx?year=2011&prog ator Conference (PACll) ram=nuchem http://www.bnl.gov/PACll

More information available in the Calendar of Events on the NuPECC website: http://www.nupecc.org/

40 Nuclear Physics News, Vol. 20, No. 4, 2010