Observation of ηc(2S) →pp¯ and search for X(3872) →pp¯ decays

Abstract

The first observation of the decay ηc(2S) →pp¯ pis reported using proton–proton collision data corre-sponding to an integrated luminosity of 3.0fb−1recorded by the LHCb experiment at centre-of-mass energies of7 and 8TeV. The ηc(2S)resonance is produced in the decay B+→[c¯ c]K+. The product of branching fractions normalised to that for the J/ψintermediate state, Rηc(2S), is measured to be Rηc (2S) ≡ B(B+→ηc(2S)K+ )×B(ηc(2S)→ p¯p ) B(B+→ J/ψ K+)×B( J/ψ → p¯p ) = (1.58±0.33±0.09)×10−2, where the first uncertainty is statistical and the second systematic. No signals for the decays B+→X(3872)(→p¯ p)K+and B+→ψ(3770)(→p¯ p)K+are seen, and the 95% confidence level upper limits on their relative branching ratios are found to be RX(3872)<0.25 ×10−2and Rψ(3770)<0.10. In addition, the mass differences between the ηc(1S)and the J/ψstates, between the ηc(2S)and the ψ(2S)states, and the natural width of the ηc(1S)are measured as M J/ψ − Mηc (1S) = 110.2±0.5 ±0.9MeV, Mψ(2S) − Mηc (2S) = 52.5±1.7±0.6MeV, ηc (1S) = 34.0±1.9±1.3MeV.