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arXiv 1407.2865hep-exhep-phnucl-ex
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稀有带电π介子衰变的实验研究

Experimental study of rare charged pion decays

Dinko Pocanic, Emil Frlez, Andries van der Schaaf

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34 pages, 20 figures, 1 table; submitted to Journal of Physics G: Nuclear and Particle Physics, for the focus section on "The low energy precision frontier", guest edited by Barry Holstein
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摘要：

简单的动力学，少量的可用衰变通道，以及非常好的控制辐射和环路校正的组合，使带电π介子衰变成为测试弱费米子耦合的基本对称性和普遍性的敏感手段，以及提高我们对π介子结构和手征动力学的理解。本文综述了带电π介子的允许稀有衰变：（a）轻子，$π^+ \to e^+ν_e$，或$π_{e2}$;（b）辐射，$π^+ \to e^+ν_eγ$，或$π_{e2γ}$，和$π^+ \to e^+ν_e e^+e^-$，或$π_{e2ee}$;（c）半轻子，$π^+\to π^0 e^+ ν$，或$π_{e3}$的实验研究现状。总的来说，合并后的数据集呈现了一个内部一致的画面，也与标准模型预测一致。内部的一致性很好地说明了$π_{e2}$分支比的$(R_{e/μ}^π)^{\rm PIBETA} = (1.2366 \pm 0.0064) \times 10^{-4}$在这项工作中提取的PIBETA测量的$π_{e3}$衰变和当前最佳值的CKM矩阵元素$V_{ud}$。然而，即使经过近几十年的巨大进步，实验精度远远落后于所有上述过程的理论描述。我们审查的影响，目前的知识和前景，在短期内进一步改善。

英文摘要：

The combination of simple dynamics, small number of available decay channels, and extremely well controlled radiative and loop corrections, make charged pion decays a sensitive means for testing the underlying symmetries and the universality of weak fermion couplings, as well as for improving our understanding of pion structure and chiral dynamics. This paper reviews the current state of experimental study of the allowed rare decays of charged pions: (a) leptonic, $π^+ \to e^+ν_e$, or $π_{e2}$, (b) radiative, $π^+ \to e^+ν_eγ$, or $π_{e2γ}$, and $π^+ \to e^+ν_e e^+e^-$, or $π_{e2ee}$, and (c) semileptonic, $π^+\to π^0 e^+ ν$, or $π_{e3}$. Taken together, the combined data set presents an internally consistent picture that also agrees well with standard model predictions. The internal consistency is illustrated well by the $π_{e2}$ branching ratio of $(R_{e/μ}^π)^{\rm PIBETA} = (1.2366 \pm 0.0064) \times 10^{-4}$ extracted in this work from the PIBETA measurement of the $π_{e3}$ decay and the current best value for the CKM matrix element $V_{ud}$. However, even after the great progress of the recent decades, experimental precision is lagging far behind that of the theoretical description for all above processes. We review the implications of the present state of knowledge and prospects for further improvement in the near term.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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