Observation of a peaking structure in the J/ψφ mass spectrum from B^± → J/ψφK^± decays

A peaking structure in the J/ψφ mass spectrum near threshold is observed in B^± →J/ψφK^± decays, produced in pp collisions at √s = 7 TeV collected 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.) MeV and Γ=28⁺¹⁵₋₁₁(stat.) ±19 (syst.) MeV, respectively. Evidence for an additional peaking structure at higher J/ψφ mass is also reported.