$CP$ asymmetries in the $\Lambda_c^+\to pK^0_S$ and $\Xi^+_c\to \Sigma^+K^0_S$ decays

Abstract

$CP$ asymmetry is a crucial element in interpreting the matter-antimatter asymmetry in the universe and searching for new physics beyond the Standard Model. In this work, we study the $CP$ asymmetries in the $\Lambda_c^+\to pK^0_S$ and $\Xi^+_c\to \Sigma^+K^0_S$ decays. The time-independent and time-integrated $\Gamma$-, $\alpha$-, $\beta$-, and $\gamma$-defined $CP$ asymmetries in the chain decay $\mathcal{B}_{c\overline 3}\to \mathcal{B}K(t)(\to \pi^{+}\pi^{-})$ are derived. It is found that the $CP$ asymmetry in $K^0-\overline K^0$ mixing cancels out in the $\alpha$-, $\beta$-, and $\gamma$-defined $CP$ asymmetries. The $U$-spin analysis shows that the amplitudes of the $\Lambda_c^+\to pK^0$, $\Lambda_c^+\to p\overline K^0$, $\Xi^+_c\to \Sigma^+ K^0$, and $\Xi^+_c\to \Sigma^+ \overline K^0$ modes are not independent. The hadronic parameters determining $CP$ asymmetries in the $\Lambda_c^+\to pK^0_S$ and $\Xi^+_c\to \Sigma^+K^0_S$ decays could be extracted from the $K^0_S-K^0_L$ asymmetry and decay parameters $\alpha$, $\beta$, and $\gamma$ in these two decay modes. We find the $CP$-violating effect induced by the interference between charmed hadron decay and neutral kaon mixing in the $\Xi^+_c\to \Sigma^+ K^0_S$ decay could reach to be $\mathcal{O}(10^{-3})$, which is several times larger than those in $D$ meson decays and at the same order as the $CP$ asymmetry in $K^0-\overline K^0$ mixing. In contrast, the same term in the $\Lambda_c^+\to pK^0_S$ mode are one order of magnitude smaller. Thus, the $\Xi^+_c\to \Sigma^+ K^0_S$ decay is a promising mode for observing $CP$ asymmetry in the charmed hadron sector and verifying the $CP$-violating effect induced by the interference between charm decay and neutral kaon mixing.