Amplitude analysis of the radiative decay B0 s → K+K−γ

Abstract

A search for radiative decay of B0 s mesons to orbitally excited K+K− states is performed using proton proton collisions recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1 . The dikaon spectrum in the mass range mKK < 2400 MeV/c 2 is dominated by the ϕ(1020) resonance that accounts for almost 70% of the decay rate. Considering the possible contributions of f2(1270), f ′ 2 (1525) and f2(2010) meson states, the overall tensor contribution to the amplitude is measured to be F{f2} = 16.8 ± 0.5 (stat.) ± 0.7 (syst.)%, mostly dominated by the f ′ 2 (1525) state. Several statistically equivalent solutions are obtained for the detailed resonant structure depending on whether the smaller amplitudes interfere destructively or constructively with the dominant amplitude. The preferred solution that corresponds to the lowest values of the ft fractions along with constructive interference leads to the relative branching ratio measurement B(B0 s → f ′ 2γ) B(B0 s → ϕγ) = 19.4 +0.9 −0.8 (stat.) +1.4 −0.5 (syst.) ± 0.5 (B)%, where the last uncertainty is due to the ratio of measured branching fractions to the K+K− fnal state. This result represents the frst observation of the radiative B0 s → f ′ 2 (1525)γ decay, which is the second radiative transition observed in the B0 s sector.