Pion Decay Experiments

一些风味物理测量和标准模型预测之间的紧张关系正在积累。特别是，一些差异暗示了轻子耦合的非普适性和CKM夸克混合矩阵的非么正性，这引发了人们对高精度测量的极大兴趣。一项名为先锋的新实验正在开发中，以提供高精度的测量，这可能会为轻子普适性和CKM统一性提供新的线索。先驱者的目标是研究Pienu分支比(pion衰变到正电子，pion衰变到muon)，pionβ衰变和其他罕见的反应。它可能位于加拿大的TRIUMF或瑞士的保罗·谢勒研究所(PSI)。这些设备可以提供强度高、能量低的介子束，可以被阻止在目标上，以精确测量稀有的介子衰变。提案已经(或正在)提交给这两个实验室。新成立的先驱合作包括来自TRIUMF的PIENU实验、PSI的PEN的专家，以及参与了费米实验室Muon g-2实验活动和ATLAS的罕见Kaon衰变和低能量受阻Muon实验的国际合作者。本申请寻求对加拿大先锋小组的初步支持，该小组由来自TRIUMF和UBC的四名首席调查人员组成。该应用侧重于与实验的核心元素--量热仪--相关的开发。与现有的Pienu分支比和介子β衰变测量相比，该量能器的精度提高了一个数量级，在能量分辨率和堆积抑制方面必须满足严格的要求，以应对更高的介子率并实现无与伦比的系统效应抑制。配备最先进的真空紫外线传感器的大型液体氙气探测器是主要竞争者，但必须进行高级模拟研究和相关的研发，以确定最佳配置和预测探测器的整体性能。这些问题在这项提案中得到了解决。

Tensions between some flavor physics measurements and Standard Model predictions are accumulating. In particular some discrepancies hint at non-universality of lepton couplings and non-unitarity of the CKM quark mixing matrix which are triggering great interest in high precision measurements. A new experiment, PIONEER, is being developed to provide highly precise measurements which could shed new light on both lepton universality and CKM unitarity. PIONEER is aimed at studying the pienu branching ratio (pion decay to positron over pion decay to muon), pion beta decay and other rare reactions. It may be located at TRIUMF, Canada or at the Paul Scherer Institut (PSI), Switzerland. These facilities can provide intense low energy pion beams which can be stopped in a target for precise measurements of rare pion decays. Proposals have been (or are being) submitted to both laboratories. The newly formed PIONEER collaboration consists of experts from the PIENU experiment at TRIUMF, PEN at PSI, as well as international collaborators who have been involved in rare kaon decay and low energy stopped muon experiments, in the Fermilab Muon g-2 experimental campaign and ATLAS. This application seeks initial support for the Canadian PIONEER team consisting of four principal investigators from TRIUMF and UBC. The application focuses on developments related to a central element of the experiment: the calorimeter. Targeting an order of magnitude improvement in precision with respect to existing measurements of the pienu branching ratio and pion beta decay, the calorimeter has to fulfill stringent requirements in terms of energy resolution and pile-up suppression to cope with higher pion rates and enable unequaled suppression of systematic effects. A large liquid xenon detector instrumented with state-of-the-art vacuum ultraviolet sensors is the leading contender but advanced simulation studies and associated R&D have to be performed to determine the optimal configuration and to predict the overall performance of the detector. These issues are addressed in this proposal.