CMS-BPH-21-003
Observation of new structure in the J/ψJ/ψ mass spectrum in proton-proton collisions at s√ = 13 TeV
A search is reported for near-threshold structures in the J/ψJ/ψ invariant mass spectrum produced in proton-proton collisions at √s = 13 TeV from data collected by the CMS experiment, corresponding to an integrated luminosity of 135 fb−1. A new structure is observed with a significance above 5 standard deviations at a mass of 6552 ± 10 (stat) ± 12 (syst) MeV. Another structure with even higher significance is found at a mass of 6927 ± 9 (stat) ± 4 (syst) MeV, which is consistent with the X(6900) resonance reported by the LHCb experiment and confirmed by the ATLAS experiment. Evidence for another new structure, with a local significance of 4.1 standard deviations, is found at a mass of 7287+20−18 (stat) ± 5 (syst) MeV. The masses and significances are obtained in a model without considering possible quantum mechanical interference between the resonances. Incorporating this interference provides a better description of the mass spectrum between the resonances and shifts the measured masses by up to 150 MeV.