Experimental Studies of Broken Symmetries with Muons, Pions and Photons

[00:72 . 200]格林量子色动力学（QCD）是公认的夸克和胶子强相互作用的理论。在低能量下，夸克和胶子被限制在重子（三个夸克）和介子（夸克-反夸克对）中，从QCD的角度理解重子和介子的性质和相互作用是至关重要的。量子光盘具有许多基本对称性。它们包括同位旋对称，即相互作用不受u，d夸克风味旋转的影响，以及手性对称，即相互作用不受左，右手夸克的单独风味旋转的影响。这些对称性的实现是丰富多样的，涉及所谓的自发、显式和异常对称性破缺效应。理解它们的实现对于理解重子和介子的低能相互作用至关重要。本实验研究探讨了低能过程中对称性的表现。在加拿大温哥华的TRIUMF实验室，我们正在研究μ子和介子束的手性和同位旋对称性。例如，介子和质子之间的弱相互作用是手性对称破缺的关键测试，而介子和质子之间的强相互作用是理解同位旋破缺的核心。此外，在弗吉尼亚州纽波特纽斯的杰斐逊实验室，我们正在合作对中性介子的衰变速率进行精确测量——这是对QCD中异常对称性破缺的独特测试。

0072200Gorringe Quantum chromodynamics (QCD) is the accepted theory of thestrong interactions of quarks and gluons. At low energies the quarksand gluons are confined in baryons (three quarks) and mesons(quark--antiquark pairs), and understanding the properties andinteractions of baryons and mesons in terms of QCD is of fundamental importance. QCD possess a number of elementary symmetries. They include isospin symmetry, whereby the interactions are unaltered by u,d quark flavor rotations, and chiral symmetry, whereby the interactions are unaltered by separate flavor rotations for left, right handed quarks. The realization of these symmetries is rich and varied, involving so-called spontaneous, explicit and anomalous symmetry breaking effects. Understanding their realization is central to understanding the low energy interactions of baryons and mesons. This experimental research addresses the manifestation of symmetries in low energy processes. At the TRIUMF Laboratory in Vancouver, Canada we are investigating chiral and isospin symmetries with beams of muons and pions. For example the weak interaction between muons and protons is a key test of chiral symmetry breaking and the strong interaction between pions and protons is central to understanding the breaking of isospin. In addition, at the Jefferson Laboratory in Newport News, Virginia we are collaborating on a precision measurement of the decay rate of the neutral pion - a unique test of anomalous symmetry breaking in QCD.