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arXiv 0811.3748hep-ph
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$B_c$跃迁形状因子的协变光阵面方法

Covariant Light-Front Approach for $B_c$ transition form factors

Wei Wang, Yue-Long Shen, Cai-Dian Lü

摘要:

在协变光前夸克模型中,我们研究了$B_c$衰变为$D, D^*, D_s, D_s^*, η_c, J/ψ, B, B^*, B_s, B_s^*$介子的形状因子。直接计算类空区域$q^2<0$中的形状因子。为了将形状因子外推到完整的运动学区域,我们通过从类空区域采用三参数形式来拟合形状因子。$b\to u,d,s$在最大反冲点处的转变形状因子($q^2=0$)小于$b\to c$和$c\to d,s$转变形状因子,而$b\to d,s,c$在零反冲点处的转变形状因子彼此接近。在拟合过程中,我们发现形状因子$A_2(B_c\to B^*)$和$A_2(B_c\to B^*_s)$的参数强烈地依赖于$B^*$和$B_s^*$介子的衰变常数。幸运的是,半轻子和非轻子$B_c$衰变对这些形状因子并不敏感。利用这些形状因子,我们还研究了半轻子$B_c\to Mlν$衰变的分支分数和极化。半轻子$B_c\to (η_c,J/ψ)lν$和$B_c\to (B_s,B_s^*)lν$衰变比$B_c\to (D,D^*,B,B^*)lν$有更大的分支分数。在三种$B_c\to Vlν$衰变中,纵向极化矢量和横向极化矢量的贡献相当。这些预测将在正在进行和即将进行的强子对撞机上得到检验。

英文摘要:

In the covariant light-front quark model, we investigate the form factors of $B_c$ decays into $D, D^*, D_s, D_s^*, η_c, J/ψ, B, B^*, B_s, B_s^*$ mesons. The form factors in the spacelike region $q^2<0$ are directly evaluated. To extrapolate the form factors to the full kinematic region, we fit the form factors by adopting a three-parameter form from the spacelike region. $b\to u,d,s$ transition form factors at maximally recoiling point ($q^2=0$) are smaller than $b\to c$ and $c\to d,s$ transition form factors, while the $b\to d,s,c$ form factors at zero recoiling point are close to each other. In the fitting procedure, we find the parameters for the form factors $A_2(B_c\to B^*)$ and $A_2(B_c\to B^*_s)$ strongly depend on the decay constants of $B^*$ and $B_s^*$ mesons. Fortunately, the semileptonic and nonleptonic $B_c$ decays are not sensitive to these form factors. With the form factors, we also investigate the branching fractions, polarizations of the semileptonic $B_c\to Mlν$ decays. Semileptonic $B_c\to (η_c,J/ψ)lν$ and $B_c\to (B_s,B_s^*)lν$ decays have much larger branching fractions than $B_c\to (D,D^*,B,B^*)lν$. In the three kinds of $B_c\to Vlν$ decays, contributions from the longitudinal polarized vector is comparable with those from the transversely polarized vector. These predictions will be tested at the ongoing and forthcoming hadron colliders.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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