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arXiv 1302.4427hep-ex
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用KLOE探测器寻找Ks介子衰变中的CP对称性破坏

Search for the CP symmetry violation in the decays of Ks mesons using the KLOE detector

M. Silarski

摘要:

这项工作的目的是确定KS -> 3 π 0衰变分支比和eta 000参数的模量,定义为KS -> 3 π 0与KL -> 3 π 0衰变的振幅比,其表征该衰变中的CP对称性破坏。测量是在位于弗拉斯卡蒂的意大利国家核物理中心的φ工厂DAFNE使用KLOE探测器进行的。通过对穿过漂移室的KL介子进行记录,并与KLOE电磁量能器相互作用,高效率地鉴别出KS介子。KS四动量矢量,然后确定使用登记的位置的KL介子和已知的动量的phi介子。接下来,通过选择具有六个伽马量子的事件来进行KS -> 3 pi 0-> 6伽马衰变的搜索,其中使用电磁量热计测量的时间和能量来重建动量。为了提高KS介子的识别后,需要六个重建的光子的判别分析进行的背景比的信号。它是基于运动学拟合,测试的信号和背景假设和开发的KS衰减到2 pi 0和3 pi 0的运动学的差异。因此,我们得到了在90%置信水平BR(KS-> 3 pi 0)< 2.7 x 10^-8时KS -> 3 pi 0分支比的上限,这几乎比最新发表的结果低5倍。在这项工作中提出的KS -> 3 pi 0衰变的搜索未能检测到足够统计显著性的信号。该上限可以转换为对η 000参数的模量的限制,在90%置信水平下,η 000参数等于:|eta000| < 0.009。

英文摘要:

The aim of this work was to determine the KS -> 3pi0 decay branching ratio and a modulus of the eta000 parameter, defined as the ratio of amplitudes for KS -> 3 pi0 to KL -> 3pi0 decays, which characterizes the CP symmetry violation in this decay. The measurement has been carried out with the KLOE detector operating at the phi-factory DAFNE in the Italian National Center for Nuclear Physics in Frascati. The KS mesons were identified with high efficiency via registration of these KL mesons which crossed the drift chamber without decaying and then interacted with the KLOE electromagnetic calorimeter. The KS four-momentum vector was then determined using the registered position of the KL meson and the known momentum of the phi meson. Next, the search for the KS -> 3pi0 -> 6gamma decay was carried out by the selection of events with six gamma quanta which momenta were reconstructed using time and energy measured by the electromagnetic calorimeter. To increase the signal over background ratio after identification of the KS meson and requiring six reconstructed photons a discriminant analysis is performed. It is based on kinematical fit, testing of the signal and background hypotheses and exploiting of the differences in kinematics of the KS decays into 2pi0 and 3pi0. Hence, we have obtained the upper limit on the KS -> 3pi0 branching ratio at the 90% confidence level BR(KS -> 3pi0)< 2.7 x 10^-8, which is almost five times lower than the latest published result. The search for the KS -> 3pi0 decay presented in this work failed to detect a signal of sufficient statistical significance. This upper limit can be translated into a limit on the modulus of the eta000 parameter amounting to: |eta000| < 0.009 at the 90% confidence level.

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