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arXiv 2103.08775hep-lathep-exhep-ph
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格点量子色动力学的$Λ_b \to Λ_c^*(2595,2625)\ell^-\barν$形状因子

$Λ_b \to Λ_c^*(2595,2625)\ell^-\barν$ form factors from lattice QCD

Stefan Meinel, Gumaro Rendon

摘要:

我们首次用晶格QCD方法确定了描述半轻子衰变$Λ_b \to Λ_c^*(2595)\ell^-\barν$和$Λ_b \to Λ_c^*(2625)\ell^-\barν$的形状因子,其中$Λ_c^*(2595)$和$Λ_c^*(2625)$分别是具有$J^P=\frac12^-$和$J^P=\frac32^-$的最轻粲重子.这些衰变模式为检验轻子味普适性提供了新的机会,同时也在$b\to c$半轻子衰变强相互作用的全局分析中发挥了重要作用。我们确定的矢量,轴向矢量,和张量形状因子的两个衰变,但只有在一个小的运动区域附近的零反冲点。晶格计算使用三种不同的规范场配置与PDMATHAMT口味的畴壁费米子的合奏,我们进行外推的形状因子的连续极限和物理π介子质量。我们提出了标准模型预测的差分衰减率和角度观测。在考虑的运动学区域中,发现$\frac12^-$最终状态的差分衰减率比$\frac32^-$最终状态的速率大约2.5倍。我们还测试我们的形状因子的结果与零反冲和规则的兼容性。

英文摘要:

We present the first lattice-QCD determination of the form factors describing the semileptonic decays $Λ_b \to Λ_c^*(2595)\ell^-\barν$ and $Λ_b \to Λ_c^*(2625)\ell^-\barν$, where the $Λ_c^*(2595)$ and $Λ_c^*(2625)$ are the lightest charm baryons with $J^P=\frac12^-$ and $J^P=\frac32^-$, respectively. These decay modes provide new opportunities to test lepton flavor universality and also play an important role in global analyses of the strong interactions in $b\to c$ semileptonic decays. We determine the full set of vector, axial vector, and tensor form factors for both decays, but only in a small kinematic region near the zero-recoil point. The lattice calculation uses three different ensembles of gauge-field configurations with $2+1$ flavors of domain-wall fermions, and we perform extrapolations of the form factors to the continuum limit and physical pion mass. We present Standard-Model predictions for the differential decay rates and angular observables. In the kinematic region considered, the differential decay rate for the $\frac12^-$ final state is found to be approximately 2.5 times larger than the rate for the $\frac32^-$ final state. We also test the compatibility of our form-factor results with zero-recoil sum rules.

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