Development of Polarization Experiments at Z^0 Energies

1994年，通过开发一套广泛的反馈系统和在倾倒环中安装无缝真空管，SLC的性能得到了显著改善，并成功地展示了未来大型直线对撞机技术在TeV地区的现实。这些反馈系统是保持低发射率的挑战。它们补偿了从昼夜温度变化到高达数十赫兹频率的束流轨道扰动等环境影响。它们控制两束在相互作用点(IP)处的束流能量和最佳重叠，并在阶跃变化(如速调管的循环和互换)中起到稳定作用。轨道反馈环路被用来故意在直线交流轨道上产生颠簸，以抵消先前产生的尾迹。结果，水平发射率从大约30微弧度降到了7微弧度。1994年运行的另一个显著成功是通过平面束碰撞提高了比光度。The Flat Beams…通过将工作点从耦合谐振中移开，多个垂直尺寸为50 mm和水平尺寸为100 mm的倾倒环被从倾倒环中分离出来，现在SLD通常在IP处获得垂直尺寸为0.9 mm和水平尺寸为2.5 mm的平面束碰撞。IP在几个房间内稳定在10 mm水平内，这一特点提高了复杂反应版本的重建效率。SLC/SLD实验最显著的进步是高电子极化。利用波长为865 nm、脉冲长度为2.8 ns、能量为10mJ的脉冲圆偏振激光照射应变的GaAs阴极，SLC输出的电子在源处的偏振度在85%以上，在IP处的偏振度在75%以上。今年，SLC/SLD的运行时间为6月至2月中旬，平均光度为每小时40-55Zs或每天800Zs(创纪录的光度为10^lt；30&GT；Cm~2/秒或1,100 Zs/天)，1994年底已记录了100,000次Z，平均极化为75%。用1993年的数据(50.000个事件)测量了具有纵向极化电子束的左右截面不对称性。用康普顿散射仪和Moeller旋光仪连续监测电子极化，在详细研究探测器特性后，两者结果一致，分别为(65.7&lt；正负0.9)%和(66&lt；正负&gt；3)%。偏振测量的不确定度为-lt；正负1.3%。我们得到的最终结果是：A_&lt；LR&gt；=0.1656&lt；正-负&gt；0.0073(统计)&lt；+-负&gt；0.0032(系统)从这个测量中，定义在Z极的弱混合角被导出为besin^2rheta_W^&lt；eff&gt；=0.2292&lt；plus-minus&gt；0.0009(统计)&lt；+-负&gt；0.0004(系统)与以前的测量相比，这一结果比LEP合作进行的25次测量的平均值小了2.4%的标准差。我们对这项测量的未来计划是将A&lt；LR&>的不确定度降低到0.002的水平，与理论极限相同数量级。用1993年的Z样本进行了广泛的QCD研究。由于理论误差很大，在这些分析中不需要高事件统计。具体的工作有：α_S测量，α_S非前导B事件的味道独立性，夸克-胶子喷流差，喷流利手，以及寻找三喷流事件中的T破坏。利用CDC+VTx的良好顶点测定，确定了BB分支率。用大约2,500个B样品得到了初步的结果，R_b=0.259&lt；+--&gt；0.023(统计)&lt；+--&gt；0.061(MC模拟)。由于具有良好的顶点性和高度极化的电子束，SLC/SLD获得了探索B物理的独特机会。由于Z事件收集的数量是新物理的关键，我们计划在未来几年继续数据采集实验，记录100万个Z事件。1994年的实验已经全部通过。最重要的探测器升级之一，即将开始的“百万-Z”运行，新的VTX升级已经批准。强耦合常数α_S是由所有已有的观测数据加上一个新的观测数据综合分析得到的，α_S=0.120&lt；+--0.003(实验)&lt；+-->0.008(理论)，所得结果与其他实验结果一致。这一结果清楚地表明了由于强子电离和其他理论计算所引起的不确定性。在SLAC和日本，为了满足SLAC的政策，正在进行从现有的VMS代码到Unix的程序转换的新努力，这需要一些资源和时间来摆脱计算能力上的混乱。较少

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 besin^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