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 C9+C9′ and C10+C10′ with the Standard Model prediction is found to vary between 1.6 σ and 4 σ, depending on the choice of local form factors.