Using data samples of 89.5 and $711{\mathrm{fb}}^{-1}$ recorded at energies of $\sqrt{s}=10.52$ and 10.58 GeV, respectively, with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider, we report measurements of branching fractions of semileptonic decays ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\ell }^{+}{\nu }_{\ell }$ ($\ell =e$ or $\mu$) and the $CP$-asymmetry parameter of ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}$ decay. The branching fractions are measured to be $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{e}^{+}{\nu }_e)=(1.31\pm 0.04\pm 0.07\pm 0.38)\%$ and $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\mu }^{+}{\nu }_{\mu })=(1.27\pm 0.06\pm 0.10\pm 0.37)\%$, and the decay parameter ${\alpha }_{\mathrm{\Xi }\pi }$ is measured to be $0.63\pm 0.03\pm 0.01$ with much improved precision compared with the current world average. The corresponding ratio $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{e}^{+}{\nu }_e)/\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\mu }^{+}{\nu }_{\mu })$ is $1.03\pm 0.05\pm 0.07$, which is consistent with the expectation of lepton flavor universality. The first measured asymmetry parameter ${\mathcal{A}}_{CP}=({\alpha }_{{\mathrm{\Xi }}^{-}{\pi }^{+}}+{\alpha }_{{\overline{\mathrm{\Xi }}}^{+}{\pi }^{-}})/({\alpha }_{{\mathrm{\Xi }}^{-}{\pi }^{+}}-{\alpha }_{{\overline{\mathrm{\Xi }}}^{+}{\pi }^{-}})=0.024\pm 0.052\pm 0.014$ is found to be consistent with zero. The first and the second uncertainties above are statistical and systematic, respectively, while the third ones arise due to the uncertainty of the ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}$ branching fraction.

中文翻译：

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半轻衰变的分支分数Ξc0→Ξ−ℓ+νℓ和Ξc0→Ξ−π+的不对称参数的测量

使用 89.5 的数据样本和 $711{\mathrm{脸书}}^{-1}$ 以能量记录 $\sqrt{秒}=10.52$ 和 10.58 GeV，分别使用 KEKB 的 Belle 检测器 ${\mathrm{电子}}^{+}{\mathrm{电子}}^{-}$ 对撞机，我们报告了半轻衰变分支分数的测量 ${\mathrm{\Xi }}_C^0\to {\mathrm{\Xi }}^{-}{\ell }^{+}{\nu }_{\ell }$ ($\ell =\mathrm{电子}$ 或者 $\mu$) 和 $C磷$-不对称参数 ${\mathrm{\Xi }}_C^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}$衰变。测量支化分数为$\mathcal{乙}({\mathrm{\Xi }}_C^0\to {\mathrm{\Xi }}^{-}{\mathrm{电子}}^{+}{\nu }_{\mathrm{电子}})=(1.31\pm 0.04\pm 0.07\pm 0.38)\%$ 和 $\mathcal{乙}({\mathrm{\Xi }}_C^0\to {\mathrm{\Xi }}^{-}{\mu }^{+}{\nu }_{\mu })=(1.27\pm 0.06\pm 0.10\pm 0.37)\%$，以及衰减参数 ${\alpha }_{\mathrm{\Xi }\pi }$ 被测量为 $0.63\pm 0.03\pm 0.01$与当前的世界平均水平相比，精度有了很大提高。对应比例$\mathcal{乙}({\mathrm{\Xi }}_C^0\to {\mathrm{\Xi }}^{-}{\mathrm{电子}}^{+}{\nu }_{\mathrm{电子}})/\mathcal{乙}({\mathrm{\Xi }}_C^0\to {\mathrm{\Xi }}^{-}{\mu }^{+}{\nu }_{\mu })$ 是 $1.03\pm 0.05\pm 0.07$，这与轻子风味普遍性的预期一致。第一个测量的不对称参数${\mathcal{一种}}_{C磷}=({\alpha }_{{\mathrm{\Xi }}^{-}{\pi }^{+}}+{\alpha }_{{\overline{\mathrm{\Xi }}}^{+}{\pi }^{-}})/({\alpha }_{{\mathrm{\Xi }}^{-}{\pi }^{+}}-{\alpha }_{{\overline{\mathrm{\Xi }}}^{+}{\pi }^{-}})=0.024\pm 0.052\pm 0.014$发现与零一致。上面的第一个和第二个不确定性分别是统计的和系统的，而第三个是由于不确定性而产生的。${\mathrm{\Xi }}_C^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}$ 支化分数。