Evidence of a 𝐽/𝜓⁢𝐾0S Structure in 𝐵0→𝐽/𝜓⁢𝜙⁢𝐾0S Decays

An amplitude analysis of 𝐵0→𝐽/𝜓⁢𝜙⁢𝐾0S 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 𝐽/𝜓⁢𝐾0S system, named 𝑇𝜃𝜓⁢𝑠⁢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 𝑇𝜃𝜓⁢𝑠⁢1⁢(4000)0 state is likely to be the isospin partner of the 𝑇𝜃𝜓⁢𝑠⁢1⁢(4000)+ state, previously observed in the 𝐽/𝜓⁢𝐾+ system of the 𝐵+→𝐽/𝜓⁢𝜙⁢𝐾+ decay. When isospin symmetry for the charged and neutral 𝑇𝜃𝜓⁢𝑠⁢1⁡(4000) states is assumed, the signal significance increases to 5.4 standard deviations.