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.
Tags Run 1
Working group Charm
Principal authors @  Jake Bennett, Angelo Di Canto
Reference accepted by PRD
Links arXiv:2509.25765, Inspire,
Bibtex 
@article{Belle-II:2025xvc,
    author = "Abumusabh, M. and others",
    collaboration = "Belle-II",
    title = "{Search for $CP$ violation in $Ξ_c^+\toΣ^+h^+h^-$ and $Λ_c^+\to ph^+h^-$ at Belle II}",
    eprint = "2509.25765",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II Preprint 2025-024, KEK Preprint 2025-26",
    month = "9",
    year = "2025"
}