Clyde Cowan (left) and Frederick Reines (right) at their original 1953 experiment at the Nobel 1995 Hanford reactor which saw promising indica­ tions of neutrino interactions. (Photo Los Alamos)

he theme of the 1995 Nobel T Prize for Physics is leptons, the particles which feel the weak nuclear force, best known in nuclear beta decay. The prestigious award is shared by Frederick Reines of the University of California, Irvine, and by Martin Perl of the Stanford Linear Accelerator Center. Professor Reines' award is in recognition of his epic 1956 discov­ ery, made with Clyde Cowan at the Savannah River reactor in South Carolina, that the neutrino, predicted by Wolfgang Pauli in 1930, is a physically observable particle. Unfortunately Clyde Cowan died in 1974. Professor Perl's discovery of the tau lepton at the SPEAR elec­ tron-positron collider in 1976 was less expected, but no less important for today's Standard Model of particle reporting a tiny energy imbalance, alternative sources of neutrinos. physics. Pauli was driven in 1930 to suggest Rather than seeing neutrino emis­ that an otherwise invisible particle sion in beta decay, the aim of Reines was emitted along with an electron and Cowan's detector was to see The discovery of the neutrino when a neutron decayed into a inverse beta decay, where a neutrino proton. At first, he was reluctant to hits a proton, producing a neutron The discovery of the neutrino is talk about a particle which could not and a positron. The latter would soon traditionally described as an experi­ be detected, but by 1934 the neutrino annihilate, releasing an electron- mental verification of a bold theoreti­ had been incorporated into Enrico positron pair. In addition, Reines and cal prediction by Wolfgang Pauli. Fermi's theory of weak interactions. Cowan also wanted to detect the However Leon Lederman has Hans Bethe and Rudolf Peierls neutron, through the gamma rays pointed out that it should be the calculated the expected absorption emitted in its eventual nuclear cap­ experimentalists who get the lion's rate of neutrinos by nuclei and ture after it had slowed down. These share of the credit. Experiments concluded such particles would be gamma rays would be seen a few provided the data which 'made it undetectable. However Bethe and microseconds after the annihilating perfectly obvious' that Pauli had to Peierls had not known about the positron. This 'delayed coincidence' invent the neutrino! enormous numbers of neutrinos was the key to neutrino discovery. Looking at the same data, Niels emitted in fission reactions. In 1953, they started work with a Bohr was led to suggest that conser­ The initial idea of Reines and 300-litre drum of liquid scintillator at vation of energy inside the atom Cowan was to catch neutrinos from Hanford, Washington, and saw a would not be absolute. an underground atomic bomb explo­ slight increase in the delayed coinci­ Pauli only made his suggestion out sion. Any detector near an exploding dence signal. This was encouraging, of desperation, says Lederman, bomb would not survive, but perhaps but not enough to claim any discov­ adding 'driving a theorist as good as a detector could be dropped down ery. Pauli to desperation has been the the shaft.Such an experiment was With five times the amount of goal of red-blooded experimentalists difficult to repeat, and in the immedi­ scintillator in three tanks viewed by ever since'. ate post-war years there were 110 phototubes, they began work at With beta decay experiments powerful new reactors offering the Savannah River reactor, South

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Discoverer of the tau lepton, Martin Peri of the Stanford Linear Accelerator Center shares the 1995 Nobel Physics Prize.

than two years. By the summer of The discovery of the tau 1973 it was logging data. One of the In 1974, attention at the SPEAR experiments lined up for SPEAR was electron-positron collider at the a search for new leptons, but in Stanford Linear Accelerator Center, November 1974 had come the was focused on the famous J/psi bonanza J/psi discovery and atten­ particles. These had been discovered tion focused on getting the most out independently by teams led by of SPEAR's Mark I detector. Burton Richter at SPEAR and by Earlier, the ADONE electron- Sam Ting at Brookhaven. These positron collider at the Italian Frascati particles had heralded a fourth quark, Laboratory and the unconventional which carried a special quantum CEA Cambridge (Massachusetts) number 'charm'. machine had shown how spectacular Such a fourth quark had been electron-positron annihilations could predicted in 1970 by Sheldon be, even at lower energies, produc­ Glashow, John lliopoulos and ing a surprising number of pions and Luciano Maiani to explain the behav­ other hadrons as well as weakly Carolina. Over 100 days of running, iour of the electrically neutral current interacting particles. However they averaged three tell-tale delayed of the weak interaction when the searches for heavy leptons had been coincidences per hour. Neutrinos quark quantum number called fruitless in the energy region covered were not just symbols in equations. strangeness was involved. by ADONE. They were for real. On 14 June 1956 For a while, it looked as though the After the J/psi discovery, the Reines and Cowan triumphantly sent 'Standard Model' (the term had not SPEAR energy was inched higher in a telegram to Pauli in Zurich. Unfortu­ yet been invented) of particle physics the search for more new particles. nately the telegram was sent to the was complete with four types of Perl noticed a few events which University, not the ETH institute quarks grouped as two pairs - up/ produced an electron and a muon but where Pauli worked, but the error down and strange/charm - together no other visible particles. At 1975 was dutifully corrected. with two leptons - the electron and conferences, Perl was referring to his the muon, each with its own kind of interesting haul of 24 events as 'U' neutrino. (for unknown) states. One of those eager to understand However most other physicists were why leptons come in distinct varieties obsessed with charm. The J/psi More neutrinos was Martin Perl. Before coming to particles, composed of a charmed SLAC, Perl had been Sam Ting's quark and its antiquark, had only Neutrinos are not only produced in thesis adviser at Michigan. Always on 'hidden' charm. Somewhere there nuclear beta decay. They are also the lookout for signs of new leptons, had to be particles with 'open' charm, found, with muons, in the weak he did a long search using the two- containing only one charmed quark, decays of pions and kaons. Were the mile linac, without success. Unde­ and at a mass suspiciously close to neutrinos produced with muons from terred, he joined Richter's team at Perl's U states. Were Perl's Us due pion decay identical to those seen in the new SPEAR ring: in his pocket to open charm? nuclear beta decay? were predictions by J.J. Sakurai and However open charm was soon The question was answered in 1962 by Y.S. Tsai about what the decays seen, while Perl, working with Gary by an experiment by Leon Lederman, of heavy leptons could look like. Feldman, had accumulated over a Mel Schwartz and Jack Steinberger To avoid making it a visible budget hundred events which, he said, at Brookhaven, which showed that item, the 200-metre Stanford Posi­ defied conventional description. neutrinos come in different kinds. tron-Electron Asymmetric Ring had Others were not convinced, alleging Lederman, Steinberger and Schwartz been built by Richter on a parking lot the U events to be background noise, were awarded the Nobel Prize for at SLAC out of the laboratory's spurious effects which mimicked a Physics in 1988. operating budget for $5 million in less particle. The mass was suspiciously

30 CERN Courier, November 1995 Nobel 1995

close to the charm threshold. At the muon signal against hadronic intru­ Stanford's SLC Linear Collider and DORIS electron-positron ring at sion, the tau was discovered by the CERN's LEP electron-positron DESY, Hamburg, no U events were same detector which revealed the J/ collider showed that Nature has no seen initially. psi. It is probably the first example of room for more than three kinds of Undeterred, Perl kept talking about separate Nobel Physics Prizes neutrinos, and looking for leptons his Us and was still seeing more having been earned by the same suddenly dropped out of fashion. them. Boldly he claimed the discov­ apparatus. Precision tau physics, probing the ery of a new lepton, the tau, from the third generation of the Standard initial letter of the Greek word triton - Model, has become a minor industry 'third' - weighing in at 1777 MeV, The Standard Model at LEP, while precision measure­ much heavier than the electron at 0.5 ments of the tau mass were made at MeV and the muon at 105 MeV. If there was a third lepton, then the Beijing electron-positron collider. By 1977, independent evidence for there had to be another pair of The Workshop on Tau Lepton Phys­ the tau came in from the PLUTO quarks. Both were discovered at ics now a major feature in the inter­ detector at the DORIS ring, and by Fermilab. The fifth quark, beauty, national physics calendar. Martin Perl the time of the 1977 Lepton-Photon was revealed in 1977, and its part­ is always guest of honour. He has meeting in Hamburg this had been ner, top, in 1995. These particles been a member of CERN's Scientific joined by DASP at DORIS and the completed today's Standard Model of Policy Committee since 1991. DELCO experiment now installed at three quark pairs linked to three With tau-charm factories planned SPEAR. leptons and their corresponding (October, page 8) tau physics is Although SPEAR's Mark I detector neutrinos. assured of a bright future. received several improvements, In 1989, the arrival of higher energy notably muon shielding to protect the electron-positron collisions at

Post Doctoral Position RESEARCH ASSOCIATE THEORETICAL PARTICLE PHYSICS INDIANA UNIVERSITY

The Deutsche Elektronen-Synchrotron, DESY, in Hamburg, per­ Applications are invited for the position of forms basic research in the field of elementary particle physics by postdoctoral research associate in theoreti­ means of a High Energy Storage Ring. It is a research institute of international repute which collaborates with similar research cen­ cal particle physics, available September 1, tres throughout the world. 1996. Initial appointment is for one year, with Within the program for the advancement of young scientists of the community of major scientific laboratories, we would like to probable renewal for a second year. We offer a position for a young

seek outstanding candidates in theoretical Ph.D. graduate particle physics who have overlapping inter­ in the field of Accelerator Physics/Accelerator Technology. ests with our group. Each application should include a curriculum vitae, a description of The topics of interest are: As a study for possible future e+/e- colliders, test accelerators are research interests and accomplishments, being constructed and will shortly go into operation. Thus partici­ and a list of publications. Candidates should pation in and realisation of technical designs and theoretical ana­ lysis in the areas of superconductivity, high frequency and acce­ also have at least three letters of reference lerator physics are required. Applicants should have a Ph.D. in physics or in an allied field and be sent to; Particle Theory Group, Physics De­ not more than 32 years old. The contract will be limited to 3 years. partment, Indiana University, Bloomington, The salary will be according to the "MTV Angestellte" Group 11a. Handicapped applicants with equal qualifications will be prefered. IN 47405, USA. Applications received be­ DESY is interested in advancing the professional development of fore January 15, 1996 may receive prefer­ women and would encourage women to apply for this position. Written applications complete with certificates and references ence. Indiana University is an Equal Oppor­ should be sent to our Personnel Department before 27.11.1995.

tunity/Affirmative Action Employer. DEUTSCHES ELEKTRONEN-SYNCHROTRON DESY NotkestraBe 85, 22607 Hamburg, Germany - Tel.: 040/8998-3628

CERN Courier, November 1995 31 Lancaster University Assistant Research Astrophysicist School of Physics and Chemistry Center for Particle Astrophysics RESEARCH ASSOCIATE POSITION UNIVERSITY OF CALIFORNIA AT BERKELEY

Applications are invited for a postdoctoral The Center for Particle Astrophysics, an NSF Science and Tech­ Research Associate Position in the Particle nology Center, invites applications for the position of Center Fel­ Physics Group. The successful candidate will low. The Center is investigating the dark matter problem through four work in one of the following activities of the group. lines of experimental attack: using conventional and cryogenic detectors to detect the interaction of dark matter particles in the 1. Studies of electroweak interactions in laboratory; studying the diffuse radiation from the early universe ALEPH AT LEP at CERN. (particularly the 3K microwave background); using distant su- pernovae to determine how much dark matter exists; and stu­ 2. Deep Inelastic Scattering in the H1 group at dying the role of dark matter in the evolution of large-scale struc­ HRA at DESY. ture. The Center Fellowship is intended to provide a young 3. Detector development for the inner tracking experimentalist with the opportunity to bring fresh insight (parti­ cularly from other fields of physics) to bear on the dark matter detector for the ATLAS collaboration at the problem and take a leading role in developing new initiatives. LHC at CERN. This two-year position will start in October, 1996, with a possible 4. BaBar Collaboration at SLAC. extension for a third year. Candidates should have a Ph.D. in Physics of Astronomy. Re­ The post is supported by the PPARC in the UK. search experience at the post-doctoral level is preferred. Salary will be commensurate with experience. Interested applicants For further details and application forms please should submit a statement of their research interests, a curricu­ lum vitae, and arrange for letters of support from three referees contact Personnel Services quoting reference who are familiar with their work. These items and a letter of appli­ number L401, Bowland College, Lancaster cation should be sent to: University, Lancaster LA1 4YT, UK (Telephone Professor Bernard Sadoulet (44) 1524 846549). Application forms should be Center for Particle Astrophysics returned to Personnel by 10 December 1995. 301 LeConte Hall University of California Further information about this post can be obtai­ Berkeley, CA 94720, USA ned from Professor T Sloan The closing date for applications will be January 1, 1996. The (e-mail [email protected]). University of California is an Affirmative Action/Equal Opportuni­ ty Employer. We especially encourage applications from female The University of Lancaster is an equal and minority candidates. opportunity employer.

NFR NATURVETENSKAPLIGA FORSKNINGSRADET Swedish Natural Science Research Council RESEARCH ASSOCIATE Experimental High Energy Physics announces a Council Researcher position in The Department of Physics at Stanford University is inviting applications for a post­ EXPERIMENTAL ASTROPARTICLE PHYSICS doctoral research associate to participate in a rare KP decay experiment at Brook­ haven National Laboratory and in a long baseline neutrino experiment, MINOS, at Fermilab. Sweden has vigorous activities in both experimental and The K°decay experiment, BNL E871, looks for rare decay modes with a single event theoretical astroparticle physics. There are strong experi­ sensitivity of 10"12. The emphasis is on two body decays, u+u~, e+e_ and [fe*. Initial mental groups involved in experiments such as AMANDA five month long data taking run was concluded in June 1995 and has met its plan­ and CAPRICE. ned goals. It is expected that the experiment will run again starting in February 1996 and possibly also in 1997. The Swedish Natural Science Research Council now ex­ The MINOS experiment is designed to be sensitive to v^ve and v^vx oscillations pands these activities by inviting applications for a tenure down to sin228 = 0,01 and to Am2 values below 10~2. This experiment was recently track type Council Researcher position at the assistant/ endorsed by HEPAP as an important element of the future US high energy physics program. The neutrino beam will be produced by the protons extracted from the associate professor level. Initially the position is for 3+3 Fermilab Main Injector, currently under construction and scheduled to be comple­ years. The successful applicant is expected to join one of ted by 1999. The far detector will be a multi-kiloton magnetic spectrometer in the the Swedish research groups. The salary range will cor­ Soudan mine in Minnesota, some 730 km away. The existing Soudan 2 detector respond to that of an associate professor (SEK 255 000- will also form part of the detector apparatus. It is hoped that data taking can begin in 350 000 per year, i e USD 36 000-49 000 per year). 2001. The successful applicant will be expected to spend the first year at BNL, participa­ Applications should include a detailed curriculum vitae and ting in E871 data taking and MINOS test beam work. Subsequently it is anticipated bibliography, summary of past research, a short research that the majority of his or her time will be spent in residence at Stanford, working plan, names of three references who can be contacted mainly on MINOS simulation, design, and construction but also participating in the analysis of E871. The initial appointment will be for three years with the possibility and, at most, 10 scientific papers. The applicant is kindly of an extension. asked to state which Swedish research group he/she would Interested applicants are requested to send three letters of reference and a resume like to join. Four copies of the application and reprints, to: Professor Stanley Wojcicki also in quadruplicate, should reach the Swedish Natural SLAC Science Research Council, Box 7142, S-103 87 Stock­ PO Box 4349, MS 63 Stanford, CA 94309, USA holm, Sweden, by December 1, 1995. The applications will be accepted until December 15,1995 or until the position is Further information can be obtained from Ms Natalie Lunin, filled. Stanford University is an equal opportunity, affirmative action employer. We are at the Secretariat of NFR, Telephone: +46-8-454 42 32, especially interested in receiving applications from female and minority physicists. fax: +46-8-454 42 50, or email: [email protected] maxon motor This candid view look illustrates why maxon will be your choice for high performance motion control. The heart of all maxon motors, brushed or brush- less, is the patented rhombic winding system, providing you with the benefits of low inertia, high acceleration, low losses and zero cogging. Combined with speed redu­ cers and feedback elements, the result is an integrated servo package for velocity and positioning control sy­ stems. Motor diameter 12 to 75 mm, out­ put rating up to 250 watts.

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POST DOCTORAL RESEARCH ASSOCIATE POSTDOCTORAL POSITION EXPERIMENTAL HIGH ENERGY PHYSICS CEBAF High Resolution Spectrometer Group (Hall A) University of California, San Diego

The Continuous Electron Beam Accelerator Facility The Department of Physics at the University of California, San (CEBAF), located in Newport News, Virginia, USA, is a Diego invites applications from outstanding candidates for a Post­ world class facility for nuclear physics research. With a 4 doctoral Researcher position to work in the field of Experimental High Energy Physics. GeV high intensity, continuous wave electron accelerator, UCSD is a member of the CLEO Collaboration at the Cornell Elec­ CEBAF will explore the fundamental nature of nuclear tron Storage Ring and is committed to a strong b-physics pro­ matter with particular emphasis on quark-gluon degrees gram with the CLEO detector. The CLEO detector has recently of freedom. The physics program of the High Resolution been equipped with a three layer, three-dimensional Silicon Ver­ Spectrometer Group focuses on precision studies of elec­ tex Detector to significantly enhance its charged particle tracking capability. The successful candidate is expected to play a major tromagnetic and weak-neutral current form factors of the role in the commissioning of the silicon detector and in the inte­ nucleon and bound nucleon properties in few body sys­ gration of the silicon detector data with that from pre-existing track­ tems. The experimental equipment in Hall A, namely, a ing devices. The candidate is alsoexpected to play a leading role pair of identical 4 GeV/c High Resolution Spectrometers in physics analysis using data obtained with this upgraded detec­ equipped with a focal plane polarimeter, are expected to tor. To this end, the candidate's prior experience with charged particle tracking in general and silicon vertex detectors in particu­ be operational in 1996. lar shall be very useful. For reasons of efficiency, the selected candidate shall be posted Applications are being invited for a post-doctoral research onsite at Cornell University in Ithaca, New York. The salary is associate position for the High Resolution Spectrometer commensurate with the candidate's qualifications and will be based Group. The position requires a recent Ph.D. in Experimental on the University of California pay scale. Subatomic Physics. The successful candidate will partici­ Interested candidates should send a copy of their CV, three let­ ters of recommendation and a statement of physics interests to: pate in the commissioning of the experimental equipment Prof. Vivek Sharma, Physics Department 0319, University of in Hall A and analyze initial experiments. Demonstrated California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093- experience in the implementation and analysis of lepton- 0319, USA. Email: [email protected]. nucleus physics experiments is preferred. Interested can­ The deadline for applications is 1 December 1995. didates should send curriculum vitae and three letters of In compliance with the Immigration Reform and Control Act of 1986, individuals offered employment by the University of Califor­ reference to: CEBAF, ATTN: Employment Manager, 12000 nia will be required to show documentation to prove identity and Jefferson Avenue, Newport News, Virginia 23606, USA. authorization to work in the United States before hiring can occur. Please specify position #PT2104 and job title when ap­ The University of California is an Equal Opportunity/Affirmative plying. CEBAF is an equal opportunity, affirmative action Action Employer. employer.

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