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The Belle and Belle II experiments have collected a 1. 4 ab^-1 sample of e^+e^- collision data at centre-of-mass energies near the (nS) resonances, of which 424 fb^-1 were collected at Belle II in Run1 (2019--2022). We present a measurement of the lepton-flavour universality between electrons and muons, the search for the lepton-flavour violation decay ^- ^-^+^-, and a measurement of the e^+e^- ^+^-⁰ cross section in the energy range from 0. 62--3. 5 GeV using an initial-state radiation technique, all performed with Belle II data.
L. Corona (Thu,) studied this question.