Measurement of $A_{CP}$ in $\Xi_c^+\to\Sigma^+ h^+ h^-$ and $\Lambda_c^+\to p h^+ h^-$ decays at Belle II
| Abstract | We report decay-rate CP asymmetries of the singly-Cabibbo-suppressed decays $\Xi_c^+\to\Sigma^+ h^+ h^-$ and $\Lambda_c^+\to p h^+ h^-$, 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{alignat*}{1} Acp(\Xi_c^+\to\Sigma^+ K^+ K^-) &= (3.7\pm6.6\pm0.6)\%, \\ Acp(\Xi_c^+\to\Sigma^+ \pi^+ \pi^-) &= (9.5\pm6.8\pm0.5)\%, \\ Acp(\Lambda_c^+\to p K^+ K^-) &= (3.9\pm1.7\pm0.7)\%, \\ Acp(\Lambda_c^+\to p \pi^+ \pi^-) &= (0.3\pm1.0\pm0.2)\%, \end{alignat*} where the first uncertainties are statistical and the second systematic, agree with \CP symmetry. From these results we derive the sums \begin{alignat}{3} &Acp(\Xi_c^+\to\Sigma^+ \pi^+ \pi^-) &&\, + \, Acp(\Lambda_c^+\to p K^+ K^-) &&= (13.4 \pm 7.0\pm 0.9)\%,\\ &Acp(\Xi_c^+\to\Sigma^+ K^+ K^-) &&\, + \, Acp(\Lambda_c^+\to p \pi^+ \pi^-) &&= (\phantom{0}4.0 \pm 6.6\pm 0.7)\%, \end{alignat} 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. |
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| Tags | Run 1 |
| Working group | Charm |
| Principal authors | @ Jake Bennett, Angelo Di Canto |
| Reference | submitted to PRD |
| Links | arXiv:2509.25765, |