标题： 观测$D^+\to K^0_Sπ^0μ^+ν_μ$、轻子味普适性检验及$D^+\to \bar{K}^\ast(892)^0\ell^+ν_\ell$的首次角分析 显示英文标题

标题： Observation of $D^+\to K^0_Sπ^0μ^+ν_μ$, Test of Lepton Flavor Universality and First Angular Analysis of $D^+\to \bar{K}^\ast(892)^0\ell^+ν_\ell$

摘要： 我们报告了一项基于在3.773 GeV对心碰撞能量下利用BESIII探测器收集的$20.3\,\mathrm{fb}^{-1}$$e^+e^-$数据样本的$D^+\to K_S^0\pi^0\ell^+\nu_\ell$($\ell = e, \mu$) 半轻子衰变的研究。 首次观测到 $D^+\to K_S^0\pi^0\mu^+\nu_\mu$ 衰变，分支比为 $(0.896\pm0.017_{\rm stat}\pm0.008_{\rm syst})\%$，并以更高的精度确定了 $D^+\to K_S^0\pi^0e^+\nu_e$ 的分支比为 $(0.943\pm0.012_{\rm stat}\pm0.010_{\rm syst})\%$。 从动力学分析可以看出，主导的$\bar{K}^\ast(892)^0$成分伴随着一个$S$波贡献，该贡献占$(7.10 \pm 0.68_{\rm stat} \pm 0.41_{\rm syst})\%$总衰变率的$\mu^+$通道和$(6.39 \pm 0.17_{\rm stat} \pm 0.14_{\rm syst})\%$的$e^+$通道。 假设单极占优参数化方法，得到了强子形式因子的比值为 $r_V=V(0)/A_1(0)=1.42 \pm\, 0.03_{\rm stat} \pm\, 0.02_{\rm syst}$ 和 $r_2=A_2(0)/A_1(0)=0.75 \pm\, 0.03_{\rm stat} \pm\, 0.01_{\rm syst}$。 基于首次全面的角分布和衰变率 $CP$ 不对称性分析，完整的一组平均角分布和 $CP$ 不对称可观测量被测量为动量传递平方的函数；它们与标准模型预期一致。 在整个动量传递平方范围以及五个选定的动量传递平方区间内，未观察到 $\mu-e$ 轻子味普适性的破坏证据。 显示英文摘要

摘要： We report a study of the semileptonic decays $D^+\to K_S^0\pi^0\ell^+\nu_\ell$ ($\ell = e, \mu$) based on $20.3\,\mathrm{fb}^{-1}$ of $e^+e^-$ collision data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. The $D^+\to K_S^0\pi^0\mu^+\nu_\mu$ decay is observed for the first time, with a branching fraction of $(0.896\pm0.017_{\rm stat}\pm0.008_{\rm syst})\%$, and the branching fraction of $D^+\to K_S^0\pi^0e^+\nu_e$ is determined with the improved precision as $(0.943\pm0.012_{\rm stat}\pm0.010_{\rm syst})\%$. From the analysis of the dynamics, we observe that the dominant $\bar{K}^\ast(892)^0$ component is accompanied by an $S$-wave contribution, which accounts for $(7.10 \pm 0.68_{\rm stat} \pm 0.41_{\rm syst})\%$ of the total decay rate of the $\mu^+$ channel and $(6.39 \pm 0.17_{\rm stat} \pm 0.14_{\rm syst})\%$ of the $e^+$ channel. Assuming a single-pole dominance parameterization, the hadronic form factor ratios are extracted to be $r_V=V(0)/A_1(0)=1.42 \pm\, 0.03_{\rm stat} \pm\, 0.02_{\rm syst}$ and $r_2=A_2(0)/A_1(0)=0.75 \pm\, 0.03_{\rm stat} \pm\, 0.01_{\rm syst}$. Based on the first comprehensive angular and the decay-rate $CP$ asymmetry analysis, the full set of averaged angular and $CP$ asymmetry observables are measured as a function of the momentum-transfer squared; they are consistent with expectations from the Standard Model. No evidence for violation of $\mu-e$ lepton-flavor universality is observed in either the full range or the five chosen bins of momentum-transfer squared.