标题： η→π0 e+e- 和 η→π+π-π0 衰变中电荷共轭不变性的检验 显示英文标题

标题： Test of charge conjugation invariance in eta->pi0 e+e- and eta->pi+pi-pi0 decays

摘要： 电荷共轭C是自然界的基本对称性之一，它将粒子转化为反粒子。 这种对称性在弱相互作用中被研究，其中它完全被破坏，但在强相互作用和电磁相互作用中了解甚少。 为此，在本论文中我们研究了eta->pi+pi-pi0和eta->pi0 e+e-衰变，这些可能破坏电荷共轭对称性。 在eta->pi+pi-pi0过程中，C对称性的破坏可能表现为带电π介子能量谱之间的不对称性。 eta->pi0 e+e-衰变在电磁相互作用的一阶中被C对称性禁止，其分支比处于10^-8的水平。 因此，观察到更大的分支比可能表明涉及一阶电磁相互作用破坏电荷共轭的机制。 这两种衰变都是通过位于德国于利希研究中心的COSY同步加速器上的WASA-at-COSY探测器进行研究的。 eta介子通过pp->pp eta反应在质子束动量为2.14GeV/c的情况下产生。 总共收集了大约5x10^7个eta介子。 作为本论文框架内分析的结果，获得了eta->pi+pi-pi0衰变的Dalitz图分布。 从该分布中，我们提取了对不同最终态同位旋值的C对称性破坏敏感的不对称性参数，并且我们确定所有参数在所获得的精度范围内与零一致。 对于eta->pi0 e+e-衰变，我们没有观察到信号，因此我们估计了分支比的上限。 所确定的上限为BR(eta->pi0 e+e-)<3.7x10^-5，在90%置信水平下。 这一结果比其他实验之前得到的结果更精确。 显示英文摘要

摘要： Charge conjugation C is one of the fundamental symmetries in nature which transforms particles into antiparticles. This symmetry was studied in weak interaction where it is fully violated, but it is poorly known in the strong and electromagnetic interactions. To this end, in this thesis we investigated eta->pi+pi-pi0 and eta->pi0 e+e- decays, which might violate charge conjugation symmetry. The violation of C symmetry in eta->pi+pi-pi0 process could manifest itself as an asymmetry between energy spectra of charged pions. The eta->pi0 e+e- decay is forbidden by C symmetry in the first order of electromagnetic interaction, with the branching ratio on a level of 10^-8. Therefore, observation of a larger branching ratio could indicate a mechanism involving first order electromagnetic interaction violating charge conjugation. Both decays were investigated by means of the WASA-at-COSY detector operating at the COSY synchrotron at the Forchungszentrum Julich in Germany. The eta meson was produced via pp->pp eta reaction at the proton beam momentum of 2.14GeV/c. In total around 5x10^7 eta mesons were collected. As a result of the analysis conducted in the framework of this thesis a Dalitz Plot distribution for the eta->pi+pi-pi0 decay was obtained. From this distribution we extracted asymmetry parameters sensitive to C symmetry violation for different isospin values of the final state and we have established that all are consistent with zero within the obtained accuracy. For the eta->pi0 e+e- decay we have not observe signal and thus we estimated an upper limit for the branching ratio. The established upper limit amounts to $BR(eta->pi0 e+e-)<3.7x10^-5 at the 90% confidence level. This result is more precise than previously obtained in other experiments.