The Sudbury Neutrino Observatory Confirms the Oscillation Picture

NEWS

SOLAR PARTICLES The Sudbury Neutrino Observatory confirms the oscillation picture

The Sudbury Neutrino Observatory, from neutrino collisions produce which started taking data in 1999, flashes of light that are picked up has announced its first results on by 9500 photomultiplier tubes.The solar neutrinos, which confirm the detector is sensitive to those solar suspicion that something happens neutrinos produced via the beta to these particles on their 150 mil­ decay of boron-8. lion kilometre journey from the Sun The heavy water is the key - SNO to the Earth. is the first extraterrestrial neutrino Experiments have been monitor­ detector to use heavy water. In one ing solar neutrinos for some heavy water reaction (call it reac­ 40 years.To see neutrinos at all tion A), an electron-type neutrino demands a major effort, so meas­ can break up a target deuteron, urements are difficult and reliable Left: when a neutrino from the Sun hits a nucleus in the heavy producing two protons and an results take time to amass. As the water of the Sudbury Neutrino Observatory (SNO) detector, a faint emergent electron. Electrons can work continued, physicists began to cone of light spreads out and is picked up (green points) by the also appear from elastic scattering suspect that their experiments were surrounding light sensors. Right: schematic of the SNO detector. (reaction B), where an incoming not seeing as many solar neutrinos The detector cavity 34 m high by 22 m in diameter, is 2000 m neutrino bounces off an atomic as expected - there was a "solar underground in a nickel mine in Ontario, Canada. The 1000 tonne electron, which then recoils. neutrino problem". heavy water target is contained in a 12 m diameter acrylic vessel, However, reaction B can be pro­ Neutrinos are produced in the viewed by 9500 phototubes mounted on an 18 m diameter duced by any kind of neutrino. nuclear reactions in the Sun's core, concentric geodesic sphere. Over 241 days, SNO collected which provide the Sun's energy (the 1169 neutrino events, which were radiant light and heat which make life possible bizarre neutrino behaviour is the reason for the carefully analysed to classify them as being is only a by-product of the Sun's nuclear fur­ solar neutrino deficit - the particles are indeed due to reaction A or B. nace). If physicists think that they understand living up to their non conformist reputation. The apparent flux of solar neutrinos meas­ what happens inside the Sun, they should be Neutrinos come in three types - electron, ured via the observed rate for reaction A able to predict the number of neutrinos which muon and tau - according to their subnuclear ( 1.75 0.± 07 +0.12 - 0.11 ± 0.05 x 106 cm"2 s"\ arrive at the Earth. When measurements do parentage. When such distinct neutrino types where the three sets of errors are respectively not agree with the prediction, there is a were first discovered, it was initially believed statistical, systematic and theoretical) is dilemma - either we do not understand how that each type was immutable - a neutrino slightly lower than the precision measurement the Sun works, or neutrinos are perverse parti­ born with an electron (as in beta decay or the (2.32 ± 0.03 +0.08 - 0.07 x 106 cm"2 s"1) via cles that do not behave as expected. reactions deep inside the Sun) could continue reaction B, by the Superkamiokande detector In appraising these two alternatives, it is to show such electron character for ever. in Japan (CERN Courier September 2000 p8- important to remember that, 100 years ago, However, the non conformist reputation of SNO's measurement of the rate for reaction B physicists could not understand where the these particles led some far-sighted physicists has not yet attained this precision).The fluxes Sun got its energy from and why it hadn't yet to suspect that perhaps neutrinos were not as measured via the two reactions are differ­ burned out. Only the advent of nuclear physics immutable. Perhaps there was a small chance ent because some of the electron neutrinos in the 1930s showed how nuclear transforma­ that a neutrino could change its allegiance in produced in the Sun have "oscillated" into tions could supply such prodigious and flight. A neutrino that began its journey in other types of neutrino en route, and on arrival enduring outputs.The neutrino concept was electron class could 'oscillate' and upgrade to at SNO are no longer able to trigger reaction A. an initially hesitant postscript to this nuclear muon class. Such changed seating arrange­ Evidence for neutrino oscillations has been picture.To understand nuclear beta decay, ments en route could explain an observed seen in other situations (CERN Courier there had to be a particle that would be very deficit of electron-type solar neutrinos. September 2000 p8).The SNO result is the difficult to detect - if it could be detected at The Sudbury Neutrino Observatory (SNO) is first direct evidence for solar neutrinos oscil­ all. From the start, neutrinos acquired a repu­ a vessel containing 1000 tonnes of heavy lating on their journey to Earth. When an tation for being non conformist. water, 2000 m underground in an active nickel experiment makes its debut with such impor­ The new Sudbury results confirm that mine in Ontario, Canada. Particles resulting tant results, its future looks assured.

CERN Courier September 2001 5 NEWS

JAPAN Japan's KEKB offers unprecedented

Unprecedented luminosity (a measure of the machine's collision rate) at the KEKB Japanese B-factory electron-positron collider: the top two charts show the increase in peak and daily performance, with the milestones achieved by machine improvements. Integrated luminosity, like age, can only go in one direction, but it has effectively doubled this year at KEKB.

The KEKB Japanese B-factory collider is deliv­ due to the photoelectron cloud up to about luminosity per month are a little higherthan ering unprecedented luminosity (a measure of 900 mA.The second improvement came from those of PEP-ll/BaBar at SLAC, Stanford, the machine's electron-positron collision rate) the installation of new movable masks on the KEKB needs further improvements to continue to the international collaboration running the moving chamber in the high-energy ring to be competitive with its rival in the long run Belle experiment. Since the commissioning of (HER).This replacement, already verified at (even assuming the present luminosity of the machine in November 1998, the KEK LER in the previous year, has raised the HER PEP-II). KEKB has significant obstacles in machine team has solved many difficulties stored current limit HER 580 to 770 mA. running more than nine months a year due to and has recently made major progress - it has Third, a state-of-the-art setting was the periodic inspection of the refrigeration achieved the highest luminosity in collider achieved in the betatron tunes - very close to system required by law, expensive summer history: 4.49 x 1033 cm"2 s'1. the half-integer resonance.The vertical tunes electricity, a weak cooling system incapable of Integrated luminosities (a measure of the were raised beyond half-integer resonance handling summer heat and so on. collision "dose" administered) are 232 pb"1 lines in both rings to gain stability of the orbits Several improvements are planned during per day, 1.50 fb"1 per week and 4.83 fb"1 per as well as a wider high-luminosity area in the this summer's shutdown. More solenoid wind­ month.These are all numbers recorded by the tune spaces.The horizontal tunes, especially ings are planned in the LER. Currently the Belle detector.Total data so far collected by in LER, were set even closer to the half-integer electron-cloud effect still looks to be the Belle had reached 33.1 fb"1 by mid-July. resonance to gain the dynamic focusing effect dominant restriction on the number of KEKB luminosity has been nearly doubled of the beam-beam interaction without sacri­ bunches circulating in the LER. this year, as seen in the figure above.This was ficing the machine aperture. Other notable Currently, the collision is carried out with brought about by several machine improve­ improvements are in the orbit control, beta­ four-bucket spacing. A shorter spacing is ments. First, 1300 out of 1800 m of field-free tron tune monitor and control, beam-size essential to achieve higher luminosity, region of the arcs in the low-energy ring (LER) control, the beam-abort system, the logging because the bunch current is limited in both has been covered with solenoid windings.This system and the injectors. rings for various reasons. suppressed the vertical blow-up of the beam Though the peak luminosity and integrated The replacement of the vacuum chamber is

6 CERN Courier September 2001 NEWS

CERN luminosity New CMS visitor centre CP-violation parameter proves a star attraction In time for the summer conference season, both of the big experiments measuring the charge-parity (CP) asymmetry in the decays of B-mesons reported impressive results. The BaBar experiment at the PEP-II electron-positron collider at SLAC, Stanford, based on a sample of 32 million B pairs, reported a value for the sin26 CP-violation parameter of 0.59 ± 0.14. The BELLE experiment at the KEKB electron-positron collider at the Japanese KEK laboratory, with 31.3 million B pairs, measures the parameter as 0.99 ± 0.14 ± 0.06. These are the most precise measurements of this parameter so far. For statistical sticklers, the results are now clearly non-zero - physicists can say with confidence that CP violation happens in B decays. Using earlier measurements, the world average becomes 0.79 ± 0.12 compared to the theoretically predicted value of 0.70 ± 0.12.

planned at the interaction region (IR), where a tentative limit of the total current is given by the heating of the IR chambers. A new cham­ ber with a taller aperture will be installed in the HER downstream of the IR, as well as additional cooling systems in LER upstream. Current movable masks of absorber type are going to be replaced with spoiler-type masks Top: visitors at the opening of the new CMS visitor centre at CERN. Bottom: the 13 x6 m, to reduce damage by beam loss. 120 tonne inner cylinder of the vacuum tank that houses the superconducting magnet for Damage to the movable masks has been a the CMS experiment at CERN's LHC collider reaches the Faucille Pass, at the summit of the serious obstacle in beam operation. A solution Jura Mountains, en route to CERN. The 120 km journey from manufacturer Franc- will be thinner masks to reduce significant Comptoise Industrie, a subsidiary of the German DWE concern, took five days. The cylinder heating damage. is the largest single element of the CMS detector. Other related improvements planned for this summer are a mask protection system with the The Compact Muon Solenoid (CMS) experi­ research facility. With the closure of LEP last beam-loss monitor and the addition of a few ment, which is being carried out in year, underground visits are no longer more radiofrequency cavities to give a margin preparation for the installation of CERN's possible, and a new series of itineraries has for high-current operation. forthcoming Large Hadron Collider (LHC), been put in place, including preparations for The Belle detector at the Japanese KEKB is became one of the laboratory's star visitor LHC experiments. studying the decays of B-mesons (particles attractions during the inauguration of a new The CMS experiment is particularly well containing the fifth "b" quark), in particular visitor centre on 14 June. suited for visits, because it will be constructed the delicate violation of charge-parity (CP) Until recently, CERN's 20 000 annual visi­ almost entirely on the surface. symmetry (see above). tors were taken on a guided tour of one of the Information about CMS, including anima­ The impact of the machine's performance experiments at the Large Electron-Positron tions and live Web-cams, can be found at on this measurement was eagerly awaited. collider (LEP), the laboratory's flagship "http://cmsinfo.cern.ch".

CERN Courier September 2001 7 NEWS

USA CERN computing wins top award On 4 June in Washington's environment with other National Building computing facilities, easing Museum, Les Robertson, access to the colossal deputy leader of CERN's quantities of data that will information technology be produced by experi­ division, accepted a 21st- ments at the laboratory's century Achievement forthcoming particle accel­ award from the erator, the Large Hadron Computerworld Honors Collider, which will switch Program, on behalf of the on in 2006. laboratory. Welcoming the award, This prestigious award CERN director-general, was made to CERN for its Luciano Maiani said: "This innovative application of is an important recognition information technology to of CERN's excellence in the benefit of society, and information technology. In it followed the laboratory's Members of the team that initiated the SHIFT project at CERN. Left to right: Ben particular, it is a reward for nomination by Lawrence Segal, Matthias Schroeder, Gail Hanson (holding the Computerworld trophy), the teams of physicists on Ellison, chairman and CEO Bernd Panzer, Jean-Philippe Baud, Les Robertson and Frederic Hemmer. CERN's LEP experiments of the Oracle Corporation. who contributed to the Ellison nominated CERN in the science cate­ the 1990s, based on RISC (reduced instruc­ development and implementation of this new gory in recognition of "pioneering work in tion set computer) workstations and architecture.The prize is also an encourage­ developing a large-scale data warehouse" - specialized networks, to today's massive ment for the physicists working on the an innovative computing architecture that systems.These include thousands of Linux PC complex challenges of LHC computing." responds precisely to the global particle nodes linked by gigabit Ethernet to hundreds Hans Hoffmann, CERN's director of scien­ physics community's needs. of Terabytes of automated tape storage tific computing, commented: "In addition to The kind of computing needed to analyse cached by dozens of Terabytes of caches its major contribution to physics, CERN has particle physics data is known as high- based on commodity disk components. been a consistent innovator in information throughput computing - a field in which CERN CERN has since worked on evolving SHIFT in technology, from the Web to its current work has played a pioneering role for over a collaboration with physicists and engineers on grid computing. We are delighted with this decade. In the early 1990s a collaboration of from universities and laboratories around the prize; particularly as it demonstrates recogni­ computer scientists from the laboratory, led by world. Several collaborations with industrial tion for CERN's computing initiatives, not from Les Robertson, and physicists from many of partners have been formed as successive the academic world but from industry's lead­ CERN's member states developed a compu­ technologies were integrated into the system. ing computing experts." ting architecture called SHIFT, which allowed Today, SHIFT is in daily use by the many Also among the winners this year was Tim multiple tape, disc and CPU servers to interact physics experiments that use CERN's facilities, Berners-Lee, who received the Cap Gemini over high-performance network protocols. providing a computing service for more than Ernst & Young Leadership award for Global SHIFT'S modular design simultaneously 7000 researchers worldwide. Integration in recognition of his pioneering work allowed scalability and easy adoption of new For the future, CERN and other particle on the World Wide Web - work carried out while technologies. (For an overview of SHIFT and physics institutes are working on scaling up he was at CERN in the early 1990s. its development, see CERN Courier July pl9.) this innovative architecture to handle tens of • More information on the Computerworld Over the years, CERN has proved these thousands of nodes, and incorporating com­ Honors Programme is available at features by evolving SHIFfrom the systems of putational grid technology to link the CERN "http://www.cwheroes.org".

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8 CERN Courier September 2001 NEWS

JAPAN Magnets become more compact A new development in Japan permanent magnet to achieve that enables powerful mag­ the required magnetic fields netic fields to be obtained of greater than 4tesla. So far without using expensive elec­ such fields have only been tromagnets could open the achievable with large super­ door to smaller, special- conducting magnets. purpose particle accelerator Using suitable magnetic installations. materials such as samarium While particle accelerators cobalt, the maximum field that were invented to supply the can be attained is about high-energy beams needed to 2 tesla normally.The Halbach- pierce through nuclear barriers 1.35 2.70 4.05 type designs improved on this and see the subnuclear world, Left: this small prototype permanent magnet designed by a team from by using a geometry that most of the accelerators now Japan's National Institute of Radiological Sciences has exceeded 4 tesla effectively amplifies the in use are low-energy The inner diameter is 6 mm and the length is 150 mm. Right: field interior field. machines used for a variety of distribution inside the prototype permanent magnet. The key innovation in the applications, such as radioiso­ new idea is to use a saturated tope production, cancer therapy and ion permanent magnets as "wigglers" and "undu- iron pole in the magnetic circuit of the perma­ implantation. lators" to generate synchrotron radiation from nent magnet to introduce a higher residual In high-energy machines that take beams a captive high-energy electron beam.The field, to compress the magnetic flux, and to into the relativistic regime, the magnetic fields magnetic material of choice was initially a weaken the demagnetizing field. Fields of up have to vary and pulsed electromagnets are rare-earth/cobalt alloy. Permanent magnets to 4.45 tesla have been attained when cooled the norm. are also used in Fermilab's Antiproton to -25°C (at room temperature the field was However, for lower-energy machines and for Recycler ring (CERN Courier My pl6). 3.9 tesla). With these fields, a machine for special-purpose magnets, it can be more Motivated by the need to design compact handling hadrons (nuclei) for cancer therapy economical to use permanent magnets machines to provide beams for cancer ther­ would be less than half the diameter of cur­ instead, with no requirement for attendant apy, a team from Japan's National Institute of rent machines.The team has begun work on a power supplies, cooling or special cryogenics. Radiological Sciences, led by Masayuki permanent magnet cyclotron. Another poss­ This idea was pioneered by Klaus Halbach Kumada, collaborated with Sumitomo Special ible application would be high-energy hadron at Berkeley, who in the late 1970s introduced Metals to produce a scaled-down, prototype colliders with small beams.

CERN/RUSSIA Last LHC magnets from Siberia reach CERN The delivery of Russian magnets to equip End of a long road. Left to right: LHC transfer lines to feed CERN's new LHC collider project director Lyn Evans; CERN is now complete. director-general Luciano Maiani; Over the past two years, magnets have been Budker Institute, Novosibirsk, director steadily arriving at CERN from Novosibirsk's Alexander Skrinsky; CERN Accelerator Bud ker Institute. director Kurt Hubner. They are sitting Some 360,6 m dipoles and 180,1.4 m on the last of 360 dipole magnets and quadrupoles, now safely at CERN, will be 180 quadrupoles from Novosibirsk for installed in two new underground transfer the transfer lines to inject protons into tunnels, each about 3 km long, connecting the the LHC. SPS and LHC/LEP tunnels. One of these tun­ nels recently linked with the 27 km LHC ring Unlike the LHCs main magnets, these are not elements is handled by the Efremov Institute, (CERN Courier My p24). superconducting.The Budker Institute sup­ St Petersburg, and on quadrupole elements Each month some 10 magnet consign­ plies them under the 1993 Co-operation by the ZVI factory in Moscow.The additional ments travelled the 6000 km from Siberia, Agreement, which covers Russian participa­ manufacture and the final assembly of the each bearing two dipoles and a quadrupole. tion in the LHC. Preliminary work on dipole magnets is done at Novosibirsk..

CERN Courier September 2001 9 NEWS

CERN/SOUTH AMERICA Latin-American school marks start of a new collaboration for CERN

The first school of high-energy for strengthening the collabora­ physics organized jointly by CERN tion between Latin-American and CLAF (Centra latinoameri- countries and CERN.The following cano de fisica), Rio de Janeiro actions, mainly in the context of was held in Itacuruçâ, Brazil on CERN's LHC project, were agreed: 6-19 May and it hopefully • to continue the biennial marked the opening of a close CERN-CLAF School; collaboration between CERN and • to promote the existing and physicists in Latin America. potential collaborations by devel­ This new series of biennial oping ad hoc protocols between schools is modelled on the Latin-American funding agencies school of physics organized by and CERN, to ensure a stable CERN and the Joint Institute for financial framework for the long Nuclear Research in Dubna near timespans of current high-energy Moscow, which was, and contin­ physics activities; ues to be, instrumental in • CERN could grant Latin- fostering relations between CERN American groups access to and former socialist countries. facilities and other services, and Some 71 students attended give them priority for recuper­ the inaugural CERN-CLAF school, ating surplus equipment; 56 of them coming from eight • CERN will continue to investi­ Latin-American countries (17 gate additional funding from the from Mexico, 16 from Brazil, 11 Time out from physics: Cecilia Uribe of Mexico and Patrick Brockhill of European Union, UNESCO and . from Argentina and 12 from other the US, studying in Rio. The school location - Itacuruçâ - is an island. CERN member states with the countries), 13 from Europe and aim of increasing the exchange of two from the US. profited from the lectures, in spite of minor scientists and to enlarge the duration and The Latin-American students were centrally language problems; number of positions for Latin-American scien­ funded for all of their travel, board and lodg­ • the mixing of nationalities was important, tists, engineers and trainees at CERN; ing, while other students were funded by their and students were convinced that contact • CERN can help by investigating possibilities home institutes. Financial support came from with other students and with lecturers of inter­ of scientific, technical, industrial and public CERN, Spain, France, Portugal and Italy, in national reputation would be significant for education co-operation with Latin America; addition to Brazil, Mexico and CLAF their future careers as well as in building up • opportunities and conditions under which The students were accommodated in twin an inter-regional network of young physicists; some Latin-American countries could become and triple rooms with students from different • the contacts made at the school were also CERN observer states would be investigated. countries and regions sharing the same room, believed to be important in strengthening the A joint CERN Latin-American steering com­ This was an important factor contributing to collaboration between individuals and institu­ mittee would be set up with the goal of the success of the school. tions inside Latin America; preparing a plan of action.The draft plan will The 11 lecturers came from Europe, Latin • there was a unanimous wish for the school be submitted, for approval, to the authorities America and the US.The lectures, which were to be continued, and the Mexican physics of CERN, CLAF and the Latin-American fund­ in English, were complemented by daily dis­ community and authorities expressed their ing agencies. It will also be submitted by cussion sessions led by seven physicists from willingness to host the next event in 2003. CERN's director general to those CERN Latin America.The students presented their At the conclusion of the school, a meeting European member states willing to co­ work in an enthusiastic poster session. with representatives from CERN, several Latin- operate, as well as to the European Union and A survey carried out at the end of the American countries (Argentina, Brazil and UNESCO. Spain and Portugal have expressed school revealed that: Mexico) and funding agencies discussed an intention of submitting the plan to the next • the school was an undisputed success; strategies for continued and possibly perma­ Ibero-American meeting of presidents and • the level of the students was high, and all nent support for the CERN-CLAF School and prime ministers which is planned for 2002.

10 CERN Courier September 2001 NEWS

A student's viewpoint As one of the students at the first of stimulating exchange of information school of high-energy physics organized and many of us came back during jointly by CERN and CLAF, here are my the free time to continue the personal impressions of the school, discussions. which I believe represent the feelings of The mixture of young theorists and the other students. experimentalists was also very fruitful. The school's structure was basically The students had different physics the same as the traditional European backgrounds, so the discussions were school of high-energy physics: two enriched by different viewpoints. weeks of excellent courses, discussion The students from Europe and the sessions and free time for amusement, US, with their different culture and in physics or other leisure activities. experience in high-energy physics, were The European school is designed well integrated. Their participation was mainly to teach theoretical physics to Brazilian students Ana Amelia Machado and also important to encourage discussion experimental physicists. The Henrique Barbosa prepare their poster contributions in English. CERN-CLAF School was wisely adapted at the first CERN-CLAF school of high-energy physics. For all of these reasons, the to the Latin-American reality - young CERN-CLAF school of high-energy theorists were also accepted and lectures on provided material for discussion during the physics seems to be mandatory. It will experimental physics were added. In free time and the sessions. certainly become instrumental in introducing addition, students from the US and Europe The poster session was a very good the Latin-American community to the participated. occasion to show our work and to learn what experimental particle physics world. The lectures motivated our curiosity and others are doing. We had about three hours Erica Ribeiro Polycarpo, UFRJ Rio de Janeiro

CRYSTALS Crystals put spin on particle beam action

New investigations being made into the apparent fields are even higher, attainingthe behaviour of charged particle beams as they so-called critical field, 1016V/cm. Under these pass through crystals suggest that the very conditions, the electrons align their spin in the high electric fields inside these crystals could field in about the same time as it takes to be used to orient (polarize) the spins of the traverse the crystal, 1 ps, instead of several particles. hours. The spin of an electron can be imagined as Under these conditions the photons emit­ equivalent to a tiny current-carrying coil.This ted in the individual electron spin-flips can coil will induce a neighbouring magnetic field, also be studied. Such effects could be of which will interact with any other electromag­ interest for planned high-energy linear netic field. electron-positron colliders, such as CERN's In the early 1960s it was seen that the CLIC, and they are probably also found at the interaction of this intrinsic electron magnet­ surface of neutron stars, where the fields are ism with the magnetic field in a circular of a strength comparable to the critical field. accelerator could be used to polarize circu­ Another well-known crystal-beam effect is lating electrons.This is now routinely used to A spin-down electron (green) emits very hard "channelling", which is when the charged polarize beams of electrons in storage rings. radiation following spin-flip to the spin-up particle beam is steered through the crystal However, this polarization takes hours to state (red) during the passage of the by its interior electromagnetic fields. Using a achieve because the fields are very weak. extremely strong electromagnetic fields in a bent crystal provides a more economical way During the 1990s the NA43 collaboration single crystal. of steering a beam than conventional large at CERN made an in-depth study of what magnets. Channelling in bent crystals is happens when a high-energy beam passes coherent electric field due to the nuclear routinely used in experiments, notably the through various crystal structures. When such constituents. Moreover, if the charged par­ NA48 CP-violation study at CERN (CERN a beam penetrates a crystal, it "sees" a strong ticles are moving at relativistic speeds, the Courier July p5).

CERN Courier September 2001 11