eta_c矢量介子衰变和Lambda-bar衰变参数的实验研究

In the framework of quantum choromodynamics, the decays of eta_c into vector meson pairs (VV, V=phi,omega,rho,K*) are suppressed by the helicity selection rule; theoretical values of branching fractions for these decays are smaller than measurements by about 10 to 100 times. Especially, the decay of eta_c into omega phi is a double-OZI violation decay, and its theoretical branching fraction gets even more smaller. Using the 1.2 billion J/psi data set accumulated at BESIII, we will make precision improved measurements on the branching fractions for eta_c->phi phi, K* K*-bar, and the precision is expected to be improved by the magnitude of one order. The results of these measurements are helpful for people to understand the eta_c decay mechanism about how the helicity selection rule is violated. Additionally, using this large data sample, the decay parameters for Lambda-bar hyperon can be measured via the decay J/psi -> Lambda Lambda-bar, and the precise Lambda-bar decay parameter will allow people to test the standard model predictions on the CP violation in Lambda decays.

在微扰量子色动力学理论框架内，eta_c->VV(V=phi,omega,rho,K*)衰变是违反螺旋度选择定则的，分支比的理论计算值比实验值小10到100倍。尤其是eta_c->omega phi还是双OZI违反的衰变，它的理论期望值更小。利用BESIII上目前采集的12亿J/psi数据，我们将精确测量eta_c->phi phi, K*K*-bar 的衰变分支比，预期精度将提高一个数量级，并寻找新的衰变模式eta_c->omega omega, omega phi。这些测量结果将有助于人们洞察eta_c矢量介子衰变中的"螺旋度选择定则"的规避机制。此外，利用大统计量的J/psi样本，我们将通过J/psi->Lambda Lambda-bar衰变，精确测量Lambda-bar的衰变参数，检验标准模型对Lambda超子衰变中CP破坏的预言。

在微扰量子色动力学理论框架内，eta_c->VV(V=phi,omega,rho,K*), chi_c2->VP衰变是违反螺旋度选择定则的，分支比的理论计算值比实验值小10到100倍。尤其是eta_c->omega phi还是双OZI违反的衰变，它的理论期望值更小。利用BESIII上目前采集的12亿J/psi和340兆psi(3686)数据，我们将精确测量eta_c->phi phi, K*K*-bar 的衰变分支比，精度提高一个数量级，并寻找新的衰变模式eta_c-> omega phi, 并在chi_c2->VP的衰变中观测到了明显的长程效应。这些测量结果将有助于人们洞察eta_c，chi_c2介子衰变中的"螺旋度选择定则"的规避机制。 此外， 我们利用12亿J/psi数据，通过J/psi->Lambda Lambdabar衰变，精确测量了Lambda 和Lambdabar超子的衰变非对称参数，刷新了粒子表的记录，同时，我们在正负电子对撞机上首次观测到了超子的横向激化效应，这为利研究激化物理现象开辟了一个新的领域。四夸克态候选者Zc(3900)的自旋和宇称量子数受到物理界的广泛关注，我们利用4.23 和4.26GeV能量点采集的数据，通过振幅分析方法确定它的JP=1+.