Measurement of CP asymmetries in B⁰ K⁰S K⁰S K⁰S decays at Belle II

We report a measurement of decay-time dependent charge-parity (CP) asymmetries in B⁰ K⁰S K⁰S K⁰S decays. We use 387 10⁶ BB pairs collected at the (4S) resonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the CP-violating parameters S and C from a fit to the distribution of the decay-time difference between the two B mesons. The resulting confidence region is consistent with previous measurements in B⁰ K⁰S K⁰S K⁰S and B⁰ (cc) K⁰ decays, and with predictions based on the standard model.