A peaking structure in the J/ψφmass spectrum near threshold is observed in B±→J/ψφK±decays, produced in pp collisions at √s=7TeVcollected with the CMS detector at the LHC. The data sample, selected on the basis of the dimuon decay mode of the J/ψ, corresponds to an integrated luminosity of 5.2fb−1. Fitting the structure to an S-wave relativistic Breit–Wigner lineshape above a three-body phase-space nonresonant component gives a signal statistical significance exceeding five standard deviations. The fitted mass and width values are m =4148.0 ±2.4 (stat.) ±6.3 (syst.) MeVand Γ=28+15−11(stat.) ±19 (syst.) MeV, respectively. Evidence for an additional peaking structure at higher J/ψφmass is also reported
