Development of Polarization Experiments at Z^0 Energies

1994年，SLC的性能得到了极大的改善，研制了一套反馈系统，并在倾倒环中安装了无缝真空管，成功地证明了未来TeV级大型直线对撞机技术的现实性。它们可以补偿环境影响，从昼夜温度变化到光束轨道干扰，频率高达数十Hz。它们控制电子束能量和两个电子束在相互作用点（IP）的最佳重叠，并用于稳定阶跃变化，如速调管的循环和互换。轨道反馈回路用于消除线性轨道中的颠簸，从而消除先前产生的尾流场尾部。结果，水平发射度从30微弧度米下降到7微弧度米。1994年运行的另一个显著成就是通过平束碰撞提高了比光度。扁平梁 ...更多信息 垂直尺寸为50 mm，水平尺寸为100 mm的碰撞是通过将工作点从耦合谐振移开而从倾倒环获得的，现在SLD常规地获得垂直尺寸为0.9 mm和水平尺寸为2.5 mm的平束碰撞，实验证明，该IP在10 mm范围内稳定数小时，这一特性提高了复杂反应椎体的重建效率，SLC/SLD实验的显著进展是高电子极化。利用波长为865 nm、脉宽为2.8 ns、能量为10 mJ的脉冲圆偏振激光束辐照应变GaAs阴极，SLC输出的电子在源端极化率大于85%，在IP端极化率大于75%。在<30>1993年的50.000次观测中，测量了<LR>E_ =91.2660.02 GeV的纵向极化电子束<cm>的左右截面不对称性A_。用康普顿散射和默勒偏振仪连续监测电子的偏振态，通过对探测器特性的详细研究，两者的结果一致，分别为（65.7 <plus-minus>± 0.9）%和（<plus-minus>66.3）%。偏振测定的不确定度为<plus-minus>1.3%。我们得到的最终结果是：A_<LR>=0.1656 <plus-minus>0.0073（统计）<plus-minus>0.0032（系统）由此导出Z极处的弱混合角为：in ^2rheta_W ^<eff>=0.2292 <plus-minus>0.0009（统计）<plus-minus>0.0004（系统）与以前的测量结果相比，这个结果比LEP合作组进行的25次测量的平均值小2.4个标准偏差。我们的计划是把A_1的不确定度降低<LR>到理论极限的0.002量级。用1993年运行的Z样品进行了广泛的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。具体的工作包括：α_S测量，α_S非主导B事件多重性的味独立性，夸克-胶子喷注差异，喷注旋向性，三喷注事件中T破坏的寻找，利用CDC+VTX的良好顶点确定性，确定了BB分支比。对2,500个B样进行了初步测定，R_（B）=0.259 <plus-minus>± 0.023（stat）。<plus-minus>由于SLC/SLD具有良好的顶点和高极化电子束，因此具有探索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内继续进行数据采集实验，以记录100万个Z。1994年的试验已经全部批准。其中一个最重要的探测器升级为即将到来的“百万Z”运行，新的VTX升级已被批准。我们期望SLD能在1995年或更长时间内得到进展，用现有的所有实验数据和一个新的观测值，通过全面分析，确定了强耦合常数α_S=0.120 <plus-minus>~ 0.003（实验）~ <plus-minus>0.008（理论），所得结果与其它实验一致。这个结果清楚地表明了由于强子化和其它理论计算所引起的不确定性。在SLAC和日本，从已有的VMS程序到UNIX程序的转换正在进行中，以满足SLAC的政策，但要摆脱计算能力上的混乱还需要一些资源和时间。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