Nature2014-06-26 3:39 PM

宇称不守恒原理的再研究 Measurement of parity violation in electron–quark scattering

论文摘要 

宇称对称(或镜像对称)意味着,左右交换不改变物理定律。在弱核力作用下宇称守恒的破坏是在上个世纪50年代中期被发现的,电子散射中宇称的破坏(破缺)过去在确定粒子物理的标准模型中是重要的,现在也被用来验证该模型。这项研究报告了一个高精度电子-夸克散射实验,它以比以前通过这一散射过程所进行的惟一直接研究高五倍的精度提供了对宇称不守恒的一个测定结果。该研究的结果证实了电弱相互作用粒子物理学理论的预测,同时也对标准模型以外的宇称破缺相互作用提供了约束。

Abstract 

Symmetry permeates nature and is fundamental to all laws of physics. One example is parity (mirror) symmetry, which implies that flipping left and right does not change the laws of physics. Laws for electromagnetism, gravity and the subatomic strong force respect parity symmetry, but the subatomic weak force does not. Historically, parity violation in electron scattering has been important in establishing (and now testing) the standard model of particle physics. One particular set of quantities accessible through measurements of parity-violating electron scattering are the effective weak couplings C2q, sensitive to the quarks’ chirality preference when participating in the weak force, which have been measured directly only once in the past 40 years. Here we report a measurement of the parity-violating asymmetry in electron–quark scattering, which yields a determination of 2C2u − C2d (where u and d denote up and down quarks, respectively) with a precision increased by a factor of five relative to the earlier result. These results provide evidence with greater than 95 per cent confidence that the C2q couplings are non-zero, as predicted by the electroweak theory. They lead to constraints on new parity-violating interactions beyond the standard model, particularly those due to quark chirality. Whereas contemporary particle physics research is focused on high-energy colliders such as the Large Hadron Collider, our results provide specific chirality information on electroweak theory that is difficult to obtain at high energies. Our measurement is relatively free of ambiguity in its interpretation, and opens the door to even more precise measurements in the future.

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