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October 5, 2025Open Access

Measurement of time-dependent CP asymmetries in B⁰ K ₒ⁰ \: π^+ π^- γ decays at Belle and Belle II

Key Points

Measured CP violation parameters for B0 meson decays include C = -0.17 and S = -0.29.
Data sets from Belle II (365 fb−1) and Belle (711 fb−1) were used to analyze B0 to K0S π+ π− γ decays.
S+ and S- values are explored in the m2(K0S π+) - m2(K0S π-) plane yielding S+ = -0.57 and S- = 0.31.
Results indicate potential for further exploration of CP violation in particle physics.

Abstract

We present a measurement of the time-dependent CP asymmetry in B⁰ K ₒ⁰ \: 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 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 m² (K ₒ⁰ π^+) -m² (K ₒ⁰ π^-) plane. The measured values are C = -0. 17 0. 09 0. 04, S = -0. 29 0. 11 0. 05, S^+ = -0. 57 0. 23 0. 10 and S^- = 0. 31 0. 24 0. 05, where the first uncertainty is statistical and the second systematic.

Measurement of time-dependent CP asymmetries in B⁰ K ₒ⁰ \: π^+ π^- γ decays at Belle and Belle II

Key Points

Abstract

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