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arXiv 1904.07530hep-phhep-ex
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“PQCD +晶格”方法中的半轻子衰变$B_c \to (η_c,J/ψ) l \barν_l $

Semileptonic decays $B_c \to (η_c,J/ψ) l \barν_l $ in the "PQCD + Lattice" approach

Xue-Qing Hu, Su-Ping Jin, Zhen-Jun Xiao

备注：
18 pages, 4 figures and 4 tables. Some important modifications to the text, new parametrization for extrapolation of the form factors, new numerical results, new figure, several new references added
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摘要：

本文采用PQCD因子分解方法研究了半轻子衰变$B_c^- \to (η_c, J/ψ) l ^- \barν_l$，利用新定义的$B_c^- \to (η_c, J/ψ) l ^- \barν_l$介子的分布振幅和一种新的参数化外推形式因子，并考虑了格点QCD关于相应形式因子的结果.结果表明：（a）在考虑晶格输入的情况下，PQCD对$B_c \to (η_c,J/ψ) l \barν$衰变分支比的预测值将比相应的形状因子小约$(5-16)\%$，（b）对$R_{η_c, J/ψ}$和纵极化$P_τ$的PQCD预测值分别为$R_{η_c}=0.34\pm 0.01 , R_{J/ψ}=0.28\pm 0.01$，$P_τ(η_c) = 0.37\pm 0.01$和$P_τ(J/ψ) = -0.55 \pm 0.01$ ;以及（c）在包括晶格输入之后，理论预测稍微改变：$R_{η_c}=0.31\pm 0.01$、$ R_{ J/ψ}=0.27\pm 0.01$、$P_τ( η_c) = 0.36 \pm 0.01$和$P_τ( J/ψ) = -0.53\pm 0.01$。$R_{ J/ψ}$的理论预测与测量值在误差范围内一致，其他预测可以在不久的将来的LHCb实验中进行检验。

英文摘要：

In this paper, we studied the semileptonic decays $B_c^- \to (η_c, J/ψ) l ^- \barν_l$ by employing the PQCD factorization approach, using the newly defined distribution amplitudes of the $B_c$ meson and the new kind of parametrization for extrapolation of the form factors , and also taking into account the lattice QCD results about the relevant form factors at several points. We found the following main results: (a) the PQCD predictions for the branching ratios of $B_c \to (η_c,J/ψ) l \barν$ decays will become a little smaller by about $(5-16)\%$ when the lattice input are taken into account in the extrapolation of the relevant form factors; (b) the PQCD predictions for the ratio $R_{η_c, J/ψ}$ and the longitudinal polarization $P_τ$ are $R_{η_c}=0.34\pm 0.01 , R_{J/ψ}=0.28\pm 0.01$, $P_τ(η_c) = 0.37\pm 0.01$ and $P_τ(J/ψ) = -0.55 \pm 0.01$ ; and (c) after the inclusion of the lattice input the theoretical predictions changed slightly: $R_{η_c}=0.31\pm 0.01$, $ R_{ J/ψ}=0.27\pm 0.01$, $P_τ( η_c) = 0.36 \pm 0.01$ and $P_τ( J/ψ) = -0.53\pm 0.01$. The theoretical predictions for $R_{ J/ψ}$ agree with the measured one within errors, and other predictions could be tested in the near future LHCb experiments.

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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