Evidence of a J/ψ KS0 Structure in B0 →j/ψφ KS0 Decays

Abstract

An amplitude analysis of 0→ / ⁢ ⁢ 0S decays is performed using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. Evidence with a significance of 4.0 standard deviations of a structure in the / ⁢ 0S system, named ⁢ ⁢1⁢(4000)0, is seen, with its mass and width measured to be 3991+12−10⁢ +9−17 MeV/⁢c2 and 105+29−25⁢ +17−23 MeV, respectively, where the first uncertainty is statistical and the second systematic. The ⁢ ⁢1⁢(4000)0 state is likely to be the isospin partner of the ⁢ ⁢1⁢(4000)+ state, previously observed in the / ⁢ + system of the +→ / ⁢ ⁢ + decay. When isospin symmetry for the charged and neutral ⁢ ⁢1⁡(4000) states is assumed, the signal significance increases to 5.4 standard deviations.