Evidence for an $$\eta _c(1S) \pi ^-$$ η c ( 1 S ) π - resonance in $$B^0 \rightarrow \eta _c(1S) K^+\pi ^-$$ B 0 → η c ( 1 S ) K + π - decays

Abstract

A Dalitz plot analysis of B 0 c (1S)K + - 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 c (1S) -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 15258 +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 B 0 c (1S)K + - branching fraction is performed and gives