Study of Rare Pion Decay

稀有介子衰变的研究

• 批准号: SAPPJ-2017-00033
• 负责人: Bryman, Douglas
• 金额: $ 6.56万
• 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: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=617918
• 关键词: Study; Rare; Pion; Decay

The standard model (SM) assumes equal electroweak couplings of the three lepton generations, a hypothesis known as lepton universality which is studied at high accuracy in high- precision measurements of pion decays and other reactions. The branching ratio of pion decays to electrons and neutrinos (compared to the ordinary decay to muons and neutrinos including radiative processes), has been calculated in the SM with extraordinary precision to be RSM=1.252±0.0002 x10-4. The measured branching ratio R is highly sensitive to violations of lepton universality and other new physics processes at very high mass scales O(1 TeV). The PIENU experiment at TRIUMF recently improved experimental knowledge of R by a factor of two to 0.2% based on analysis of 10% of the data taken. The large data set collected by PIENU will enable further improvement of the precision in the measurement of the branching ratio of the pions to electrons and neutrinos by another factor of two to four. The level of experimental precision on the branching ratio of this decay relative to the ordinary decay process to a muon and neutrino is expected to be <0.1%. Another focus of the efforts will be to significantly improve the search for heavy neutrinos coupled to electrons. Our previous experiments in this field already give the most stringent limits on the presence of heavy neutrinos coupled to electrons in the mass range accessible to pion decay.

标准模型（SM）假设三个Lepton世代的电子耦合相等，这是一个称为Lepton Universe的假设，在乳腐烂和其他反应的高精度测量中以高精度进行了研究。已经在SM中计算出乳酸衰变与电子和神经元的分支比（与普通衰变与包括辐射过程在内的MUON和神经元相比），以非常精确的精度为RSM = 1.252±0.0002 x10-4。测得的分支比率R对侵犯Lepton普遍性和其他新物理过程非常敏感。根据对所采集的10％的分析，TriumF的Pienu实验最近将R的实验知识提高了2％至0.2％。 PIERU收集的大数据集将在测量普力与电子和神经元的分支比的测量比中进一步提高精度，另外两倍的因子。相对于普通衰减过程与穆恩和神经元的分支比率的实验精度水平为<0.1％。这项工作的另一个重点是显着改善对与电子结合的重型神经元的搜索。我们以前在该领域的实验已经给出了最严格的限制，即在质量衰减的质量范围内与电子产品相结合的重量。