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arXiv 0811.0775hep-phhep-ex
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Kl4衰变中的同位旋破缺

Isospin breaking in Kl4 decays

Gilberto Colangelo, Juerg Gasser, Akaki Rusetsky

摘要:

关于Ke 4衰变的数据允许人们提取关于阈值附近的弹性π π散射振幅的实验信息,并将分析的结果与QCD框架中的预测进行对抗。这些预言涉及的是一个同位旋对称的世界,而实验是在真实世界中进行的,那里的同位旋破缺效应--由电磁相互作用和上下夸克的质量差产生--总是存在的。我们讨论了需要考虑这些修正,以便与预测进行有意义的比较成为可能。特别是,我们注意到,有一个壮观的同位旋破缺效应在KE 4衰变。一旦考虑到这一点,之前关于Ke 4衰变的NA 48/2数据与π π散射长度预测之间的差异就消失了。

英文摘要:

Data on Ke4 decays allow one to extract experimental information on the elastic pi pi scattering amplitude near threshold, and to confront the outcome of the analysis with predictions made in the framework of QCD. These predictions concern an isospin symmetric world, while experiments are carried out in the real world, where isospin breaking effects - generated by electromagnetic interactions and by the mass difference of the up and down quarks - are always present. We discuss the corrections required to account for these, so that a meaningful comparison with the predictions becomes possible. In particular, we note that there is a spectacular isospin breaking effect in Ke4 decays. Once it is taken into account, the previous discrepancy between NA48/2 data on Ke4 decays and the prediction of pi pi scattering lengths disappears.

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