| Co-Investigator(Kenkyū-buntansha) |
PRESCOTT C.Y スタンフォード線型加速器センター, 教授
LEITH D.W.G. スタンフォード線型加速器センター, 教授
BREIDENBACH Martin Stanford Linear Accelerator Center, Professor, 教授
BALTAY C. エール大学, 物理学部, 教授
KAWAHARA Hideaki Stanford Linear Accelerator Center, Research Associate, 研究員
MASUDA Hiroaki Stanford Linear Accelerator Center, Research Associate, 研究員
TAKAHASHI Tohru Hiroshima University, Faculty of Science, Research Associate, 理学部, 助手 (50253050)
SUGIYAMA Akira Nagoya University, Faculty of Science, Research Associate, 理学部, 助手 (80187674)
NAGAMINE Tadashi Tohoku University, Faculty of Science, Research Associate, 理学部, 助手 (30212111)
SUEKANE Fumihiko Tohoku University, Faculty of Science, Research Associate, 理学部, 助手 (10196678)
YOSHIOKA Masakazu National Laboratory for High Energy Physics, Associate Professor, 助教授 (50107463)
NAKANISHI Tsutomu Nagoya University, Faculty of Science, Associate Professor, 理学部, 助教授 (40022735)
SUZUKI Shiro Nagoya University, Faculty of Science, Associate Professor, 理学部, 助教授 (50089851)
YUTA Haruo Tohoku University, Faculty of Science, Professor, 理学部, 教授 (90108457)
BALTY Charles Yale University, Professor
PRESCOTT Charles Stanford Linear Accelerator Center, Professor
LEITH David Stanford Linear Accelerator Center, Professor
|
|---|
| Research Abstract |
In 1994 SLC performance was dramatically improved by developing an extensive set of feedback systems, and the installation of seamless vacuum tube in the dumping ring, and succeeded to demonstrate the reality of future large linear collidertechnology in TeV region.
These feedback systems are challange for preservation of the low emittance. They compensate for enviromental effects ranging from diurnal temperature variations to beam orbit disturbances up to frequencies of tens of Hz. They control the beam enery and optimal overlap of two beams at the interaction point (IP), and serve to stabilize against step changes such as cycling and interchange of klystrons. The orbit feedback loops are used to deliberate bumps in the lineac orbit whic cancel previously generated wake field tails. As result, horizontal emittances drop from about 30 to 7 micro radian meter.
Other remarkable success in 1994 operation has been to increase the specific luminosity by the flat beam collisions. The flat beams
… More
of vertical size of 50 mm and horizontal of 100 mm are procuced from the dumping rings by shifting the operating point away from a coupling resonance, and now SLD routinely attained flat beam collisions with 0.9 mm and 2.5 mm, vertial and horizontal size respectively, at IP.The IP is tured out to be stable within 10 mm level for several houres and this feature boost up the reconstruction efficiencies of complicated reaction vertecies.
The most remarkable advance in SLC/SLD experiment is the high electron polarization. By making use of strained GaAs cathode irradiated by the pulsed circularly polarized laser beam with wavelegth of 865 nm and the pulse length of 2.8 ns with 10 mJ of energy, SLC delivered electrons with a polarization of more than 85% at the source and 75% at IP.
In this year, SLC/SLD has run from the June to the middle of February, with an average luminosity of 40-55 Zs per hour or 800 Zs per day (a record luminosity was 10^<30> cm^2/sec or 1,100 Zs per day), and has recorded more than 100,000 Z at the end of 1994 runs with an average polarization of 75%.
The left-right cross section asymmetry A_<LR> with longitudinally polarized electron beam has been measured at E_<cm>=91.2660.02 GeV with 1993 data (50.000 events). The electron polarization was continuously monitored by a Compton scattering and Moeller polarimeter, and both results were coinside, i.e. (65.7<plus-minus>0.9) % and (66<plus-minus>3) % respectively, after detailed studies of detector characteristics. The uncertainty in polarization determination was <plus-minus>1.3%. The final result we obtained is,
A_<LR>=0.1656<plus-minus>0.0073 (statistical) <plus-minus>0.0032 (systematic)
From this measurment, the weak mixing angle defined at the Z-pole is derived to be
sin^2rheta_W^<eff>=0.2292<plus-minus>0.0009 (statistical) <plus-minus>0.0004 (systematic)
Comparing with the previous measurments, this result is smaller by 2.4 standard deviations than the average of 25 measurments performed by the LEP Collaborations. Our future plan for this measurment is to reduce uncertainties in A_<LR> to the level of 0.002 the same order of magnitudes to theoretical limit.
An extensive QCD studies are performed with the Z samples of 1993 run. Since the theoretical errors are so large, the high event statistics are not requiered in these analysis. Specific subjects being done are : alpha_S mesurment, flavor independence of alpha_S non-leading multiplicity of B events, quark-gluon jet difference, jet handedness, and search for T-violation in three-jet events.
Taking advantage of good vertex determination of CDC+VTX,BB branching ratio has been determind. A preliminary result was obtained with about 2,500 B samples is,
R_b=0.259<plus-minus>0.023 (stat.) <plus-minus>0.061 (MC simulation).
With good vertexing and highly polarized electron beams, SLC/SLD has the unique opportunity exploring B physics Since the number of Z event collection is the key to the new physics, we plan to continue data aquisition experiments to record a million of Zs in the next few years. The experiment for 1994 has already approved in full. One of the most improtant detector upgrades for the comming "million-Z" runs, the new VTX upgrade has been approved. We are expecting SLD to go ahead in 1995 and further more.
Strong coupling constant alpha_S is determind by the complehensive analysis using all existing obserbvables plus a new obsevable,
alpha_S=0.120<plus-minus>0.003 (experimental) <plus-minus>0.008 (theoretical)
Obtained results are consistent with other experiments. This result indicate clearly the uncerainty due to the hadoronization and other theoretical calculations. A rapid development in QCD formalism is expected.
In SLAC and in Japan, a new efforts for the program conversion from existing VMS codes to UNIX are being proceed to meet SLAC policy, and it will take some resouces and time to get rid of confusion in computing power. Less
|
