  A peaking structure in the J/psi phi mass spectrum near threshold is observed
in B(+/-) to J/psi phi K(+/-) decays, produced in pp collisions at sqrt(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/psi, corresponds to an integrated
luminosity of 5.2 inverse femtobarns. 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 Gamma = 28 +15 -11 (stat.) +- 19 (syst.) MeV, respectively.
Evidence for an additional peaking structure at higher J/psi phi mass is also
reported.
