Evidence for an ηc(1 S) π- resonance in B0→ ηc(1 S) K+π- decays

Abstract

A Dalitz plot analysis of B0 → ηc(1S)K +π− decays is performed using data samples of pp collisions collected with the LHCb detector at centre-of-mass energies of √s = 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 4.7 fb−1. A satisfactory description of the data is obtained when including a contribution representing an exotic ηc(1S)π− resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are 4096 ± 20 +18 −22 MeV and 152±58 +60 −35 MeV, respectively. The spin-parity assignments J P = 0+ and J P = 1− are both consistent with the data. In addition, the first measurement of the B0 → ηc(1S)K +π− branching fraction is performed and gives B(B0→ ηc(1S)K +π−) = (5.73 ± 0.24 ± 0.13 ± 0.66) × 10−4, where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions.