Search for non-Standard Model Physics using the TREK Detector at J-PARC

使用 J-PARC 的 TREK 探测器搜索非标准模型物理

• 批准号: SAPPJ-2015-00035
• 负责人: Hasinoff, Michael
• 金额: $ 7.29万
• 依托单位: University of British Columbia
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=614422
• 关键词: Search; non; Standard; Model; Physics

The study of high-precision electroweak measurements has long been used as a stringent test of Standard Model (SM) predictions and any deviations from these predictions will indicate new physics. The semi-leptonic kaon decay, K+ --> lepton + neutrino (K_l2), is one of the best channels to perform such tests since lepton universality is one of the basic assumptions in the SM. By measuring the branching ratio of the electric (Ke2) and muonic (Kµ2) decay modes the hadronic form factor in Kl2 decay cancels out, and the helicity suppression in Ke2 greatly enhances the sensitivity to new physics. Our proposed stopped K+ decay experiment aims to obtain a factor of two improvement in the combined systematic and statistical uncertainty; this will allow us to test a recent prediction based on SUSY neutrino mixing. The muon background in the positron spectrum is expected to be considerably lower than in the CERN NA62 experiment. Our new E36 experiment will be performed with the upgraded TREK apparatus at J-PARC using a stopped K+ beam. The Ke2 (P=247 MeV/c) and Kµ2 (P=236 MeV/c) events emitted from the active scintillating fibre target will be momentum analyzed using a 4-layer spiral scintillating-fibre tracker and 3 MWPCs located in each gap of a 12-sector toroidal spectrometer. Momentum cuts at 228 and 215 MeV/c will remove the pi0 backgrounds from Ke3 and Kµ3, respectively. Careful electron and muon particle identification (PID) is essential in this experiment because of the large difference in branching ratios. This will be achieved using (1) threshold aerogel Cherenkov counters surrounding the target, (2) a high-resolution (100ps) measurement of the Time-of-Flight between counters located just outside the target and at the exits of the magnetic sectors, and (3) lead glass EM shower counters placed behind the TOF2 counters. The analysis procedure will be exactly identical for both Ke2 and Kµ2 events except for the PID in order to reduce the systematic uncertainty due to the analysis. The structure dependent (SD) background events will be rejected by detecting the gammas in a 768 element barrel shaped CsI(Tl) calorimeter surrounding the target region. The statistical error on the R_K value will be dominated by that of the accepted Ke2 events. Assuming a main ring power of 30 kW we expect a K+ intensity of ~200 kHz at the target position. Hence the number of accumulated Ke2 events after 50 days will be ~ 250,000, corresponding to a statistical uncertainty in deltaR_K / R_K ~ 0.2%. Detailed MC simulations indicate an overall systematic uncertainty of 0.15% after adding all items in quadrature. The statistical uncertainty can be reduced even further with more additional beam time.

高精度电弱测量的研究长期以来一直被用作标准模型（SM）预测的严格测试，任何偏离这些预测的情况都将表明新的物理学。轻子普适性是标准模型的基本假设之一，因此，半轻子K ~+ →轻子+中微子（K_12）衰变是进行这类实验的最佳途径之一。通过测量电（Ke 2）和μ子（Kµ2）衰变模式的分支比，Kl 2衰变中的强子形状因子被抵消，而Ke 2中的螺旋度抑制大大提高了对新物理的敏感性。我们提出的停止K+衰变实验的目的是获得两个因素的改善相结合的系统和统计的不确定性，这将使我们能够测试最近的预测的基础上超对称中微子混合。正电子谱中的μ子背景预计将大大低于CERN NA 62实验。 我们新的E36实验将在J-PARC使用停止的K+束进行升级的TREK设备。将使用4层螺旋偏振光纤跟踪器和位于12扇区环形光谱仪每个间隙中的3个MWPC对有源偏振光纤靶发射的Ke 2（P=247 MeV/c）和Kµ2（P=236 MeV/c）事件进行动量分析。在228和215 MeV/c的动量削减将分别从Ke 3和Kµ3中去除π 0背景。在这个实验中，仔细的电子和μ子粒子识别（PID）是必不可少的，因为分支比有很大的差异。这将通过使用（1）围绕目标的阈值气凝胶切伦科夫计数器，（2）位于目标外部和磁扇区出口处的计数器之间的飞行时间的高分辨率（100 ps）测量，以及（3）放置在TOF 2计数器后面的铅玻璃EM簇射计数器来实现。除PID外，Ke 2和Kµ2事件的分析程序完全相同，以降低分析引起的系统不确定性。结构相关（SD）的背景事件将被拒绝通过检测γ在768元素桶形CsI（Tl）量热计周围的目标区域。R_K值的统计误差将主要取决于可接受的Ke 2事件的统计误差。假设主环功率为30 kW，我们预计目标位置处的K+强度约为200 kHz。因此，50天后累积的Ke 2事件数量将为~ 250，000，对应于Δ R_K / R_K ~ 0.2%的统计不确定性。详细的MC模拟表明，在正交添加所有项目后，整体系统的不确定性为0.15%。统计不确定性可以通过更多的附加射束时间进一步降低。