Title: First measurements of the branching fractions for the decay modes $Ξ_c^{0} \to Λη$ and $Ξ_c^0 \to Λη'$ and search for the decay $Ξ_c^{0} \to Λπ^0$ using Belle and Belle II data Show Chinese title

Title: $Ξ_c^{0} \to Λη$和$Ξ_c^0 \to Λη'$的衰变模式的分支分数的首次测量以及使用 Belle 和 Belle II 数据对$Ξ_c^{0} \to Λπ^0$衰变的搜索

Abstract: Using data samples of 988.4 fb$^{-1}$ and 427.9 fb$^{-1}$ collected with the Belle and Belle II detectors, we present a study of the singly Cabibbo-suppressed decays $\Xi_c^{0} \to \Lambda \eta$, $\Lambda \eta'$, and $\Lambda \pi^0$. We observe the decay $\Xi_c^0 \to \Lambda \eta$ and find evidence for the decay $\Xi_c^0 \to \Lambda \eta'$, with corresponding branching ratios determined to be ${\mathcal{B}(\Xi_c^0 \to \Lambda \eta)}/{\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)}= (4.16 \pm 0.91 \pm {0.23})\%$ and ${\mathcal{B}(\Xi_c^0 \to \Lambda \eta')}/{\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)}= (2.48 \pm 0.82 \pm {0.12})\%$, respectively. We find no significant signal in the $\Xi_c^0 \to \Lambda \pi^0$ decay mode and set an upper limit at the 90% credibility level of ${\mathcal{B}(\Xi_c^0 \to \Lambda \pi^0)}/{\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)}< {3.5\%}$. Multiplying these ratios by the world-average branching fraction of the normalization channel, $\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)=(1.43 \pm 0.27)\%$, we obtain the absolute branching fractions of $\mathcal{B}(\Xi_c^0 \to \Lambda \eta)= (5.95 \pm 1.30 \pm {0.32} \pm 1.13) \times 10^{-4}$, $\mathcal{B}(\Xi_c^0 \to \Lambda \eta')= (3.55 \pm 1.17 \pm {0.17} \pm 0.68) \times 10^{-4}$, and an upper limit at the 90% credibility level on the absolute branching fraction of $\mathcal{B}(\Xi_c^0 \to \Lambda \pi^0)< {5.2} \times 10^{-4}$. The quoted first and second uncertainties are statistical and systematic, respectively, while the third uncertainties arise from the branching fraction of the normalization mode. These results are consistent with most theoretical predictions and further the understanding of the underlying decay mechanisms. Show Chinese abstract

Abstract: 使用Belle和Belle II探测器收集的988.4 fb$^{-1}$和427.9 fb$^{-1}$数据样本，我们研究了单Cabibbo抑制衰变$\Xi_c^{0} \to \Lambda \eta$，$\Lambda \eta'$和$\Lambda \pi^0$。 我们观察到衰变$\Xi_c^0 \to \Lambda \eta$并发现衰变$\Xi_c^0 \to \Lambda \eta'$的证据，相应的分支比分别确定为${\mathcal{B}(\Xi_c^0 \to \Lambda \eta)}/{\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)}= (4.16 \pm 0.91 \pm {0.23})\%$和${\mathcal{B}(\Xi_c^0 \to \Lambda \eta')}/{\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)}= (2.48 \pm 0.82 \pm {0.12})\%$。 我们在$\Xi_c^0 \to \Lambda \pi^0$衰变模式中未发现显著信号，并在 90% 置信度水平上设定了上限${\mathcal{B}(\Xi_c^0 \to \Lambda \pi^0)}/{\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)}< {3.5\%}$。 将这些比率乘以归一化通道的世界平均分支比$\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)=(1.43 \pm 0.27)\%$，我们得到绝对分支比$\mathcal{B}(\Xi_c^0 \to \Lambda \eta)= (5.95 \pm 1.30 \pm {0.32} \pm 1.13) \times 10^{-4}$、$\mathcal{B}(\Xi_c^0 \to \Lambda \eta')= (3.55 \pm 1.17 \pm {0.17} \pm 0.68) \times 10^{-4}$，以及在90%置信度水平上对绝对分支比$\mathcal{B}(\Xi_c^0 \to \Lambda \pi^0)< {5.2} \times 10^{-4}$的上限。 所引用的第一和第二不确定性分别为统计性和系统性，而第三种不确定性来源于归一化模式的分支比。 这些结果与大多数理论预测一致，并进一步加深了对基本衰变机制的理解。