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arXiv 2106.09463hep-ph
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半轻子$B_c$介子衰变中的轻子质量效应

Lepton mass effects in exclusive semileptonic $B_c$-meson decays

Lopamudra Nayak, Sonali Patnaik, P. C. Dash, Susmita Kar, N. Barik

摘要:

本文在基于平均味独立标量-矢量调和势的相对论独立夸克(RIQ)模型框架下,讨论了排他的半轻子$B_c$ -介子衰变:$B_c\to η_c(J/ψ)lν$和$B_c\to D(D^*)lν$.我们从RIQ模型中导出的介子波函数的重叠积分计算了代表衰变振幅的不变形状因子。为了研究半轻子衰变中的轻子质量效应,我们首先分别研究了$e^-$和$τ^-$模衰变过程中$q^2$可及运动学范围内形状因子的$q^2$依赖性.螺旋度振幅,$q^2-$光谱不同的螺旋度的贡献,和总的$q^2$ -光谱的每个衰变过程分别进行了类似的研究,在其$e^-$和$τ^-$模式。我们预测的衰变率/分支分数,向前向后的不对称性,和不对称参数与其他模型的预测,这有望在未来的实验中进行测试,在Tevatron和LHC的合理协议。我们还预测可观察到的$'R'$对应于其$e^-$模式的衰变过程中的分支分数的比率,其相应的值在$τ^-$模式。我们的结果与另一个标准模型(SM)的预测,突出了失败的轻子味普适性暗示新的物理超越SM的解释观察到的偏差观测$'R'$值从相应的SM预测。

英文摘要:

In this work, we discuss exclusive semileptonic $B_c$-meson decays: $B_c\to η_c(J/ψ)lν$ and $B_c\to D(D^*)lν$ in the framework of the relativistic independent quark(RIQ) model based on an average flavor independent confining potential in equally mixed scalar-vector harmonic form. We calculate the invariant form factors representing decay amplitudes from the overlapping integrals of meson wave functions derivable in the RIQ model. To evaluate the lepton mass effects in the semileptonic decays, we first study the $q^2$-dependence of the form factors in the accessible kinematic range of $q^2$ involved in the decay process in its $e^-$ and $τ^-$ mode separately. Similar studies on helicity amplitudes, $q^2-$spectra for different helicity contributions, and total $q^2$-spectra for each decay process are carried out separately in their $e^-$ and $τ^-$ modes. We predict the decay rates/ branching fractions, forward-backward asymmetry, and the asymmetry parameter in reasonable agreement with other model predictions, which can hopefully be tested in future experiments at the Tevatron and LHC. We also predict the observable $'R'$ which corresponds to the ratio of branching fractions for the decay process in its $e^-$ mode to its corresponding value in the $τ^-$ mode. Our results are comparable to another standard model(SM) predictions which highlight the failure of the lepton flavor universality hinting at new physics beyond SM for the explanation of the observed deviation of observable $'R'$ value from the corresponding SM predictions.

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