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We present a measurement of Rk+ , the branching fraction ratio B(B → K+μ+μ)=B(B → K*e+e),, for both charged and neutral B mesons. The ratio for the charged case R K* + is the first measurement ever performed. In addition, we report absolute branching fractions for the individual modes in bins of the squared dilepton invariant mass q2. The analysis is based on a data sample of 711 fb−1, containing 772 × 106 BB̅ events, recorded at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetricenergy e+e collider. The obtained results are consistent with standard model expectations.

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Wehle, S., Adachi, I., Adamczyk, K., Aihara, H., Asner, D. M., Atmacan, H., Aulchenko, V., Aushev, T., Ayad, R., Babu, V., Behera, P., Berger, M., Bhardwaj, V., Biswal, J., Bozek, A., Bračko, M., Browder, T. E., Campajola, M., Cao, L., … Zhulanov, V. (2021). Test of lepton-flavor universality in . Physical Review Letters, 126(16).

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