Evidence for a Narrow Near-Threshold Structure in the J/psi phi Mass Spectrum in B+ -> J/psi phi K+ Decays

Abstract

Evidence is reported for a narrow structure near the J/psi phi threshold in exclusive B+ -> J/psi phi K+ decays produced in (p) over barp collisions at root s = 1.96 TeV. A signal of 14 +/- 5 events, with statistical significance in excess of 3.8 standard deviations, is observed in a data sample corresponding to an integrated luminosity of 2.7 fb(-1), collected by the CDF II detector. The mass and natural width of the structure are measured to be 4143.0 +/- 2.9(stat) +/- 1.2(syst) MeV/c(2) and 11.7(-5.0)(+8.3)(stat) +/- 3.7(stat) Mev/c(2).