【作者】 于波；

【导师】 左亚兵；

【作者基本信息】 辽宁师范大学 ， 粒子物理与原子核物理， 2021， 硕士

【摘要】 重介子遍举衰变在检验粒子物理标准模型(SM)、寻找SM以外的新物理、SM基本参数的确定等方面起着非常重要的作用。其中,味改变中性流(FCNC)诱导的稀有衰变在SM中是通过圈效应产生的,对新物理(NP)非常敏感。B、Bs包含一个b夸克,是典型的重介子,可以用重夸克展开的方法进行处理,同时由于其遍举衰变丰富的物理内涵,相关稀有衰变过程是检验SM、寻找NP的理想场所。目前人们对于S波介子(末态为标量和矢量介子)的研究较多,而对于P波介子的相关研究较少。本文主要是在重夸克有效场论(HQEFT)的框架内,利用光锥求和规则(LCSR)对B、Bs到P波轻张量介子稀有半轻衰变做一个较为系统的研究。本文首先对相关研究背景和理论框架进行了简要的综述,主要包括B、Bs介子半轻稀有衰变的实验研究现状和P波介子的物理性质两个方面。工作部分则在HQEFT的框架下,利用LCSR计算了B、Bs到轻P波张量介子(a2(1320)、K2*(1430)、f2(1270)、f2’(1525))的形状因子。计算中我们考虑张量介子光锥分布振幅到扭度3并采用了级数展开的方法对形状因子进行了参数化。利用给出的形状因子结果,我们对相关FCNC诱导的稀有半轻衰变进行了系统的研究,在不同末态轻子对不变质量平方区域计算了分支比BR、纵向极化分数<FL>、前后不对称<AFB>和角分布可观测量<P1>、<P2>、<P4’>、<P5’>。研究表明,SM预言的分支比达到了 O(10-8)量级,误差约为15%,主要来自形状因子的不确定性。其它可观测量由于是通过振幅比值定义的,误差都很小。另外,我们也模型无关的考虑了新物理对上述可观测量的贡献。这些新物理效应都是通过对威尔逊系数C9,10eff的修正体现出来的,我们共考虑了4个新物理方案。研究表明,大多数可观测量在SM和不同新物理方案下给出的结果都是相近的,但也有一些可观测量的结果差别较大,这些结果可以被将来更为精确的实验所检验并用于区分不同的新物理模型。更多还原

【Abstract】 Heavy meson exclusive decays play an important role in testing the standard model of particle physics(SM),probing new physics beyond the SM,and determining its basic parameters.Among these,the rare decays induced by the flavor changing neutral current(FCNC)are generated by loop effects in the SM and therefore are very sensitive to new physics.B,Bs both contain a b quark and are typical heavy mesons.These decays can be dealt with via the heavy quark expansion.Furthermore,due to rich physical contents,the relevant rare decays are ideal places for testing the SM and looking for new physics.At present,there are many studies on the processes with the final states containing only S-wave mesons(scalar and vector mesons),while there are few studies on the decays involving P-wave mesons.In this thesis,we intend to give a systematic study on the rare semileptonic decays of B,Bs to light P-wave tensor mesons by using the light cone sum rules(LCSR)in the framework of heavy quark effective field theory(HQEFT).First of all,we give a brief review for the relevant research background and theoretical framework,which mainly includes two parts,i.e.the status of experiments on B,Bs rare semileptonic decays and physical properties of P-wave mesons.In the working part,the transition form factors of B,Bs to light P-wave tensor mesons(a,(1320),K2*(1430),f2(1270),f2(1525))are calculated by using the LCSR in the framework of HQEFT.The light cone distribution amplitudes(DAs)of tensor mesons are consider to twist-3 and the series expansion are adopted in the parameterization of form factors.With the form factors given here,we give a systematic study on relevant FCNC induced rare semileptonic decays.The branching ratio BR,longitudinal polarization fraction<FL>,forward-backward asymmetry<AFB>and angular distribution observables<P1>,<P2>,<P’4’>,<P’5’>are measured in bins of dilepton invariant mass square(q2).It is found that the the branching ratios reaches the order of O(10-8)and the uncertainties are about 15%,mainly come from the form factors.In contrast,other observables are defined via the ratios of amplitudes and corresponding uncertainties are much smaller.In addition,we also consider the contributions of new physics to the above obseravables model independently.These effects of new physics are all appear as corrections to the Wilson coefficients C9,10 eff.In total,we consider 4 new physics scenarios.Research shows that the predictions of SM and different new physics scenarios are similar for most observable,while there are also some observables which have quite different results.These results may be tested by more precise experiments in the future and used to distinguish different new physics models.更多还原