HQEFT框架内半轻衰变B_(s)→K_(2)(1820)lν-_(l)的相关研究

Investigations on the B_(s)→K_(2)(1820)lν-_(l) semileptonic decays in HQEFT

在重夸克有效场论(HQEFT)框架内,利用光锥求和规则(LCSR)对Bs到J^(PC)=2^(--)张量介子K_(2)(1820)半轻衰变进行了研究.首先,基于K_(2)(1820)光锥分布振幅,重夸克展开至领头阶,利用LCSR计算了Bs→K_(2)(1820)的跃迁形状因子.计算表明,与相应2++张量介子情形不同,在所取自由参数范围内,形状因子V_(2)<0.在此基础上,预言了半轻衰变B_(s)→K_(2)(1820)lν-_(l)的可观测量,包括分支比、纵向极化分数、前后不对称和微分前后不对称过零点.研究显示,电子和μ轻子末态分支比几乎相等,在10^(-5)量级,相应τ轻子末态分支比约为前者的1/5.纵向极化分数均>0.8,大于相应2^(++)张量介子情形.前后不对称随着末态带电轻子质量的增大而增大.这些结果有可能在将来被LHCb、BelleⅡ等更为精确的实验所检验.

The semileptonic B s decays into J^(PC)=2^(--) tensor meson K_(2)(1820) are investigated by using the light cone sum rules (LCSR) in the framework of heavy quark effective field theory (HQEFT). Firstly,to the leading order of heavy quark expansion,the relevant B s→K_(2)(1820) form factors are calculated via LCSR based on the distribution amplitudes of K_(2)(1820) meson. We found that the form factor V_(2) is negative in the region of free parameters chosen,which is different with the case of 2 ++ tensor meson in the final state. On this basis,we predict the observables for B_(s)→K_(2)(1820)lν-_(l) semileptonic decays,including the branching ratio,longitudinal polarization fraction,forward-backward asymmetry and zero-crossing point of differential forward-backward asymmetry. It is found that the branching ratios for the decay modes with e or μ in the final state are almost identical,at the order of 10^(-5) ,while the branching ratio for the decay with τ is about one fifth of the former. The longitudinal polarization fractions are all above 0.8,larger than the case of 2^(++) tensor meson. And the forward-backward asymmetries increase with the mass of charged lepton in the final state. These results may be tested by more precise experiments such as LHCb,Belle Ⅱ in the future.