Measurement of the time-dependent $CP$ asymmetry in $B^0 \to K_S^0 \pi^{+} \pi^{-} \gamma$ decays

Abstract We present a measurement of the time-dependent $CP$ asymmetry in $B^0 \to K_{\rm S}^0 \: π^{+} π^{-} γ$ decays using a data set of 365 fb$^{-1}$ recorded by the Belle II experiment and the final data set of 711 fb$^{-1}$ recorded by the Belle experiment at the ${\rm Υ(4S)}$ resonance. The direct and mixing-induced time-dependent $CP$ violation parameters $C$ and $S$ are determined along with two additional quantities, $S^{+}$ and $S^{-}$, defined in the two halves of the $m^2(K_{\rm S}^0 π^{+})-m^2(K_{\rm S}^0 π^{-})$ plane. The measured values are $C = -0.17 \pm 0.09 \pm 0.04$, $S = -0.29 \pm 0.11 \pm 0.05$, $S^{+} = -0.57 \pm 0.23 \pm 0.10$ and $S^{-} = 0.31 \pm 0.24 \pm 0.05$, where the first uncertainty is statistical and the second systematic.
Tags Belle Run 1 Run 2 (partial)
Working group Time Dependent CP Violation
Principal authors @  Varghese Babu, Jerome Baudot, Sviatoslav Bilokin, Giulio Dujany, Tristan Fillinger, Christian Finck, Pere Gironella Gironell, Isabelle Ripp-Baudot, Petros Stavroulakis
Reference published in JHEP
Document BELLE2-PUB-PH-2025-014
Links arXiv:2510.01331, Inspire,
Bibtex 
@article{Belle-II:2025mid,
    author = "Abumusabh, Merna and others",
    collaboration = "Belle-II, Belle",
    title = "{Measurement of time-dependent $CP$ asymmetries in $B^0 \to K_{S}^0 \pi^{+} \pi^{-} \gamma$ decays at Belle and Belle II}",
    eprint = "2510.01331",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II preprint: 2025-001, KEK preprint: 2024-49",
    month = "10",
    year = "2025"
}