▲ 作者：The T2K Collaboration
▲ 連結：
https://www.nature.com/articles/s41586-020-2177-0
▲ 摘要
輕子的CP破壞可以通過一種稱為輕子發生的過程產生物質-反物質差異已被證實。在標準模型的帶電電流相互作用下的輕子混合，通過一種複雜的相δCP提供了CP破壞的潛在來源，而這恰為一些輕子生成的理論模型所需要。
這種CP破壞可以用介子中微子到電子中微子的振蕩以及相應的反中微子振蕩來測量，這些中微子振蕩可以用由T2K（從東海到神岡的中微子實驗）和新星實驗建立的加速器產生的光束進行實驗。
在此，我們報告一個使用通過T2K實驗觀測到的長基線中微子和反中微子振蕩的測量，結果顯示大大增加了中微子振蕩的概率，排除了導致大量增加反中微子振蕩概率三個標準差（3σ）的δCP值。
三個標準差的δCP置信區間每2π循環重複，一般質量序為[−3.41, −0.03]，反向質量序為[−2.54, −0.32]。
我們的結果表明，輕子中存在CP破壞，我們的方法能夠利用加速器產生的中微子束，在中微子振蕩中敏感搜索物質-反物質不對稱性。未來用更大的數據集進行測量將檢驗輕子CP破壞是否大於夸克的CP破壞。
▲ Abstract
It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis. Leptonic mixing, which appears in the standard model’s charged current interactions, provides a potential source of CP violation through a complex phase δCP, which is requiredby some theoretical models of leptogenesis. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments. Until now, the value of δCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δCP, which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks.