Measurement of the local and nonlocal amplitudes in B+ → K+μ+μ− decays

This paper presents a thorough study of the local and nonlocal amplitudes in B + → K + μ + μ − transitions through an amplitude analysis of the dimuon mass spectrum of the decay. The analysis is based on pp collision data corresponding to an integrated luminosity of 8.4 fb − 1 collected by the LHCb experiment during Run1 and Run2. This measurement employs a model that describes both one-particle and two-particle nonlocal amplitudes across the entirety of the dimuon mass spectrum, enabling the determination of both short- and long-distance contributions to the decay. The compatibility of the Wilson coefficient combinations ${C}_9+{C}_9^{\prime }$ and ${C}_{10}+{C}_{10}^{\prime }$ with the Standard Model prediction is found to vary between 1 . 6 σ and 4 σ , depending on the choice of local form factors.