Search for $CP$ violation in $\Xi_c^+\to\Sigma^+h^+h^-$ and $\Lambda_c^+\to ph^+h^-$ at Belle II

Abstract

We report decay-rate $CP$ asymmetries of the singly-Cabibbo-suppressed decays $\Xi_c^+\to\Sigma^+h^+h^-$ and $\Lambda_c^+\to ph^+h^-$, with $h=K,\pi$, measured using 428 fb$^{-1}$ of $e^+e^-$ collisions collected by the Belle II experiment at the SuperKEKB collider. The results, \begin{equation} A_{CP}(\Xi_c^+\to\Sigma^+K^+K^-) = (3.7\pm6.6\pm0.6)\%, \end{equation} \begin{equation} A_{CP}(\Xi_c^+\to\Sigma^+\pi^+\pi^-) = (9.5\pm6.8\pm0.5)\%, \end{equation} \begin{equation} A_{CP}(\Lambda_c^+\to pK^+K^-) = (3.9\pm1.7\pm0.7)\%, \end{equation} \begin{equation} A_{CP}(\Lambda_c^+\to p\pi^+\pi^-) = (0.3\pm1.0\pm0.2)\%, \end{equation} where the first uncertainties are statistical and the second systematic, agree with $CP$ symmetry. From these results we derive the sums \begin{equation} A_{CP}(\Xi_c^+\to\Sigma^+\pi^+\pi^-) \, + \, A_{CP}(\Lambda_c^+\to pK^+K^-) = (13.4 \pm 7.0\pm 0.9)\%, \end{equation} \begin{equation} A_{CP}(\Xi_c^+\to\Sigma^+K^+K^-) \, + \, A_{CP}(\Lambda_c^+\to p\pi^+\pi^-) = (\phantom{0}4.0 \pm 6.6\pm 0.7)\%, \end{equation} which are consistent with the $U$-spin symmetry prediction of zero. These are the first measurements of $CP$ asymmetries for individual hadronic three-body charmed-baryon decays.