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 JHEP 01, 134 (2026), DOI: 10.1007/JHEP01(2026)134
Document BELLE2-PUB-PH-2025-014
Links arXiv:2510.01331, Inspire, JHEP
Bibtex 
@article{Belle:2025pmi,
    author = "Abumusabh, Merna and others",
    collaboration = "Belle, Belle-II",
    title = "{Measurement of time-dependent CP asymmetries in ${B}^{0}\to {K}_{\text{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",
    doi = "10.1007/JHEP01(2026)134",
    journal = "JHEP",
    volume = "01",
    pages = "134",
    year = "2026"
}