ing full use of the existing TRISTAN Cornell (superconducting single- KEK complex. cell) are both viable, but need to be B factory plans The current plan for the KEK B- fully investigated. A feedback sys Factory is a double-ring collider of tem will also be necessary to sup unequal energies, to be installed in press the instabilities. There is a To boost the study of B mesons a newly constructed tunnel 1.2km practical design for high vacuum, (carrying the heavy b quark), the in circumference. The TRISTAN but ideas are needed for cooling a Japanese KEK Laboratory is look Main Ring is also a possibility. The beam pipe at the collision point. ing to construct a B-meson 'fac beam energies, 8 GeV on 3.5 GeV, The next steps are to identify tory'. are optimized for CP studies at the critical beam experiments possible B-mesons have revealed unex upsilon 4S peak. More asymmetric at existing storage rings, and to in pected and important quark phy collisions, 12 GeV on 2.5 GeV, itiate international collaboration on sics. Well-known examples are the may also be required for the meas important items such as cavities, a long lifetime of the B-mesons, indi urement of rapid oscillation be feedback system, beam ducts and
cating a large gap between the tween the neutral Bs meson (con the beam pipe at the collision third and second quark generation taining the strange- and b-quarks) point. (compared to that between the and its antiparticle. This is also ac Detector construction would second and the first), and relatively commodated in the design. benefit from TRISTAN experience. large mixing of the neutral B-meson The beams would be supplied Tracking chambers and electro and its antiparticle, now interpreted from the upgraded 2.5 GeV Linac, magnetic calorimeters can be as being due to a heavy sixth stored and accelerated in the TRIS based on presently available tech ('top') quark (see page 5). TAN Accumulation Ring, and then niques. A large superconducting However the potential richness injected into the storage rings. The solenoid of 1 Tesla class and an of B-meson physics has not been design luminosity at the first stage iron structure currently operating in fully explored. In particular a large is 2 x 1033 per sq cm per s, with the TRISTAN experiments will also violation of CP symmetry (com 400 bunches colliding head-on, ev become available. bined left-right reflection and parti- entually reaching 1034 with 2000 However there are special requi cle-antiparticle reversal) is expected bunches colliding at an angle. rements for a detector at an asym with B-mesons. (The only CP viola To appraise the present design, metric B factory. Excellent vertex tion observed so far, in the neutral an International Workshop on resolution, better than 100 mi kaon sector, is a small effect.) A Asymmetric B-Factory Accelera crons, in the beam direction is nec long-standing mystery, CP violation tors was held at KEK from 4-6 essary to separate the decays of might have played an essential role October. Thirty experts from 'moving Bs', and a double-sided in the formation of the present abroad and forty from Japan parti silicon-strip detector is under inten matter (rather than antimatter) uni cipated in four working groups - sive study. Fast readout electronics verse. Also quark generation mix lattice design, beam-beam interac is another requirement, resulting ing reflecting possible new physics tion, hardware issues and the inter from a short beam-crossing interval can be examined at the deepest action region. The KEK design em and a high event rate. VLSI tech level through B-meson decays. ploys a small beta compression, nology will be fully incorporated. Thus a variety of B-meson physics small bunch spacing and a high Finally, the detector should be able projects are being discussed world tune-shift limit as well as a large to fully reconstruct as many indi wide (June 1990, page 10). dynamic aperture. No serious prob vidual B decays as possible, requir The particle physics programme lem has been identified. ing ingenious combinations of de at KEK aims for a clean and de However, any high event rate tector techniques, either existing or tailed study of quark-lepton physics factory-type accelerator is full of shortly to become available. with electron-positron collisions. technical challenges. In particular Funding negotiations with the While R and D work is rapidly gain closely spaced particle bunches are Japanese government project have ing momentum for the Japan Linear susceptible to coupled-bunch insta begun. If everything goes well, Collider (JLC), which will attack the bilities in accelerating cavities. construction will start next year TeV energy scale, B meson phy Damped cavities under investiga and finish by the end of 1995, with sics can be started earlier by mak tion at KEK (Palmer-type) and at most of the work done while TRIS-
CERN Courier, January/February 1991 21 When a storage ring is operated with multi ple beam bunches, even distant bunches can interact with each other through resonating accelerator components, such as radiofre- quency cavities. This can produce unwanted cavity fields, giving coupled-bunch instabili ties and poor performance. In the damped cavity design for the pro posed B-factory at the Japanese KEK Labo ratory, harmful field components are mini mized.
TAN continues to run. An International Workshop on Physics and Detectors for the KEK High energy electrons for probing nuclei Asymmetric B-Factory will be held from 15-18 April to give the final It is becoming increasingly clear ness in probing details of nu polish to the experimental plan and that the quarks hidden deep in clear structure, and in the US, to discuss ongoing international side the proton and neutron con the CEBAF Continuous Electron collaboration. Further information stituents of nuclei can play an Beam Accelerator Facility being from F.Takasaki (Fax 0298-64- important role in nuclear behav built at Newport News, Virginia, 2580, Bitnet TAKASAKI at iour. to provide energies up to 4 GeV JPNKEKVM). With quark field theory (quan will open up new nuclear phy tum chromodynamics - QCD) sics horizons. one of the twin pillars of today's In France, a report published SUPERCOLLIDER Standard Model, the implications last year (May 1990, page 17) Preparing initial of this physics at the nuclear underlined the importance of experiments level are being widely investi setting up an essentially Euro gated. pean project to provide nuclear This new emphasis has been physicists with electron beams The Superconducting Supercollider marked by the migration of of even higher energies, beyond (SSC) Laboratory in Ellis County, hundreds of nuclear physicists 10 GeV Texas, has taken an important step to new research pastures at high To push this message home, toward its scientific programme. energy Laboratories - CERN's a workshop was organized late While three letters of intent for LEAR antiproton ring, and ion last year at Dourdan, France, at large detectors had been invited, beams at CERN and Brookhaven. tended by some 200 partici only two could be considered due In addition, medium energy el pants, including many young re to funding limitations. Two letters ectron machines (around 1 GeV) searchers. were received from existing colla have demonstrated their useful borations (SDC and L*) and one from a merger of (EMPACT and TEXAS). Pushing for European nuclear physics - Ingo The SSC Laboratory has decided Sick of Basle, left, with Bernard Frois of Sa- that the SDC collaboration will have clay. support for a full technical propo (Photo Maurice Jacob) sal. The Laboratory will carry out a detailed cost review of the pro posed L* detector. EMPACT/TEX- AS was not approved and the Lab oratory will help these physicists participate in the programme. In the current financial year, SSC funding from federal sources amounts to $267M ($243M of new money plus $24M of 1990 construction money held over) compared to the $318M re quested, but the State of Texas has compensated with an addition al $60M to give $149M, hence to tal funding of $416M, including $7M for Department of Energy management.
22 CERN Courier, January/February 1991