Testing Lepton Flavor Universality and CKM Unitarity with Rare Pion Decays in the PIONEER experiment
Testing Lepton Flavor Universality and CKM Unitarity with Rare Pion Decays in the PIONEER experiment
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发表时间：
2022-03
影响因子：
6.3
通讯作者：
P. C. W. Altmannshofer;H. Binney;E. Blucher;D. Bryman;L. Caminada;S. Chen;V. Cirigliano;S. Corrodi;A. Crivellin;S. Cuen-Rochin;A. Canto;L. Doria;A. Gaponenko;A. García;L. Gibbons;C. Glaser;M. E. Godoy;D. Goldi;S. Gori;T. Gorringe;D. Hertzog;Z. Hodge;M. Hoferichter;S. Ito;T. Iwamoto;P. Kammel;B. Kiburg;K. Labe;J. LaBounty;U. Langenegger;C. Malbrunot;S. Mazza;S. Mihara;R. Mischke;T. Mori;J. Mott;T. Numao;W. Ootani;J. Ott;K. Pachal;C. Polly;D. Povcani'c;X. Qian;D. Ries;R. Roehnelt;B. Schumm;P. Schwendimann;A. Seiden;A. Sher;R. Shrock;A. Soter;T. Sullivan;M. Tarka;V. Tischenko;A. Tricoli;B. Velghe;V. Wong;E. Worcester;M. Worcester;C. Zhang
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作者：
P. C. W. Altmannshofer;H. Binney;E. Blucher;D. Bryman;L. Caminada;S. Chen;V. Cirigliano;S. Corrodi;A. Crivellin;S. Cuen-Rochin;A. Canto;L. Doria;A. Gaponenko;A. García;L. Gibbons;C. Glaser;M. E. Godoy;D. Goldi;S. Gori;T. Gorringe;D. Hertzog;Z. Hodge;M. Hoferichter;S. Ito;T. Iwamoto;P. Kammel;B. Kiburg;K. Labe;J. LaBounty;U. Langenegger;C. Malbrunot;S. Mazza;S. Mihara;R. Mischke;T. Mori;J. Mott;T. Numao;W. Ootani;J. Ott;K. Pachal;C. Polly;D. Povcani'c;X. Qian;D. Ries;R. Roehnelt;B. Schumm;P. Schwendimann;A. Seiden;A. Sher;R. Shrock;A. Soter;T. Sullivan;M. Tarka;V. Tischenko;A. Tricoli;B. Velghe;V. Wong;E. Worcester;M. Worcester;C. Zhang
描述了先锋实验的物理动机和概念设计，这是一项测试轻子普适性和CKM统一性的新一代稀有介子衰变实验。这项先驱实验的第一阶段是由Paul Scherrer研究所提出并批准的，旨在测量带电介子与电子的分枝比，R_e/Mu，比目前的实验结果高15倍，达到标准模型(SM)预测的1/10^4美元的精度。考虑到SM预测和指向轻子味道普适性的潜在破坏的数据之间的几个不一致，先驱实验将通过对新粒子的量子效应的敏感性来探索这些反常的非SM解释，直到PeV质量尺度。这项先驱实验的后期工作旨在提高介子β衰变分枝比的实验精度，目前为1.036(6)×10-8，提高了三倍(第二阶段)和一个数量级(第三阶段)。这种对BRPB的精确测量将允许根据Cabibbo角异常来测试CKM的单位性，并在0.02水平上从理论上最清洁地提取$|V_{ud}|$，可与从超允许的β衰变中推断的结果相媲美。
The physics motivation and the conceptual design of the PIONEER experiment, a next-generation rare pion decay experiment testing lepton flavor universality and CKM unitarity, are described. Phase I of the PIONEER experiment, which was proposed and approved at Paul Scherrer Institut, aims at measuring the charged-pion branching ratio to electrons vs.\ muons, $R_{e/\mu}$, 15 times more precisely than the current experimental result, reaching the precision of the Standard Model (SM) prediction at 1 part in $10^4$. Considering several inconsistencies between the SM predictions and data pointing towards the potential violation of lepton flavor universality, the PIONEER experiment will probe non-SM explanations of these anomalies through sensitivity to quantum effects of new particles up to the PeV mass scale. The later phases of the PIONEER experiment aim at improving the experimental precision of the branching ratio of pion beta decay (BRPB), $\pi^+\to \pi^0 e^+ \nu (\gamma)$, currently at $1.036(6)\times10^{-8}$, by a factor of three (Phase II) and an order of magnitude (Phase III). Such precise measurements of BRPB will allow for tests of CKM unitarity in light of the Cabibbo Angle Anomaly and the theoretically cleanest extraction of $|V_{ud}|$ at the 0.02\% level, comparable to the deduction from superallowed beta decays.