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Development of Polarization Experiments at Z^0 Energies

Z^0 能量偏振实验的进展

基本信息

批准号：
04044076
负责人：
KAJIKAWA Ryoichi
金额：
$ 12.48万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1994
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-04044076/
关键词：
Stanford linear Accelerator Center (SLAC)SLAC Electron-Positron Linear Accelerator (SLC)SLAC Large Detector (SLD)Polarized electron beam Z^0 boson Electroweak interaction Left-right asymmetry in coross section Standard model in particle p

项目摘要

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

1994年，通过开发一套广泛的反馈系统以及在倾倒环中安装无缝真空管，SLC的性能得到了显着提高，并成功地证明了未来大型线性对撞机技术在TeV区域的现实。这些反馈系统是保持低发射率的挑战。它们可以补偿从昼夜温度变化到频率高达数十赫兹的光束轨道扰动等环境影响。它们控制相互作用点 (IP) 处的光束能量和两束光束的最佳重叠，并用于稳定速调管的循环和互换等阶跃变化。轨道反馈回路用于在线性轨道中故意颠簸，从而消除先前生成的尾流场尾部。结果，水平发射率从大约 30 微弧度米下降到 7 微弧度米。 1994 年操作中的其他显着成功是通过平面光束碰撞增加了比光度。通过将工作点从耦合谐振移开，从倾倒环产生垂直尺寸为 50 毫米和水平尺寸为 100 毫米的扁平梁，现在 SLD 可以在 IP 处常规地实现垂直尺寸和水平尺寸分别为 0.9 毫米和 2.5 毫米的扁平梁碰撞。事实证明，IP 在数小时内稳定在 10 毫米水平内，这一特性促进了重建 SLC/SLD实验最显着的进步是高电子极化。 SLC利用应变GaAs阴极，在波长865 nm、脉冲长度2.8 ns、能量10 mJ的脉冲圆偏振激光束照射下，发射出电子，源极极化率超过85%，IP极化率达75%。今年，SLC/SLD已从6月运行到2月中旬，平均光度为40-55 Zs/小时或每天 800 Zs（创纪录的光度为 10^<30> cm^2/sec 或每天 1,100 Zs），并在 1994 年底记录了超过 100,000 Zs，平均偏振率为 75%。在 E_<cm>=91.2660.02 处测量了纵向偏振电子束的左右横截面不对称性 A_<LR> GeV 与 1993 年数据（50.000 个事件）。通过康普顿散射和莫勒旋光计连续监测电子极化，在对探测器特性进行详细研究后，两个结果一致，分别为（65.7±0.9）％和（66±3）％。偏振测定的不确定度为<正负>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）由此测量，在Z极处定义的弱混合角导出为besin^2rheta_W^<eff>=0.2292<plus-minus>0.0009（统计） <正负>0.0004（系统）比较与之前的测量结果相比，该结果比 LEP 协作组织执行的 25 次测量的平均值小 2.4 个标准差。我们对该测量的未来计划是将 A_<LR> 的不确定性降低到 0.002 的水平，与理论极限相同的数量级。使用 1993 年运行的 Z 样本进行了广泛的 QCD 研究。由于理论误差很大，因此在这些分析中不需要高事件统计数据。正在进行的具体课题有：α_S测量、α_S非主导B事件多重性的风味独立性、夸克-胶子射流差异、射流旋向性以及三射流事件中T破坏的搜索。利用CDC+VTX良好的顶点确定，已经确定了BB分支比。用大约2,500个B样本得到的初步结果是，R_b=0.259<正负>0.023（统计）<正负>0.061（MC模拟）。凭借良好的顶点和高极化电子束，SLC/SLD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，我们计划继续数据采集实验来记录未来几年内将有数百万个 Z。 1994年的实验已经完全通过。新的 VTX 升级已获得批准，这是即将到来的“百万 Z”运行中最重要的探测器升级之一。我们期待SLD在1995年及以后继续发展。强耦合常数α_S是通过对所有现有的可观测量加上一个新的可观测量进行综合分析确定的，α_S=0.120<正负>0.003（实验）<正负>0.008（理论）得到的结果与其他实验一致。这一结果清楚地表明了由于强质化和其他理论计算而导致的不确定性。预计 QCD 形式主义将快速发展。在 SLAC 和日本，正在进行从现有 VMS 代码到 UNIX 的程序转换的新努力，以满足 SLAC 政策，并且需要一些资源和时间来消除计算能力的混乱。较少的