Observation of $\eta_{c}(2S) \to p \bar p$ and search for $X(3872) \to p \bar p$ decays

The first observation of the decay ηc(2S)→pp¯ is reported using proton–proton collision data corresponding to an integrated luminosity of 3.0 fb−1 recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ηc(2S) resonance is produced in the decay B+→[cc¯]K+ . The product of branching fractions normalised to that for the J/ψ intermediate state, Rηc(2S) , is measured to be Rηc(2S)≡B(B+→ηc(2S)K+)×B(ηc(2S)→pp¯)B(B+→J/ψK+)×B(J/ψ→pp¯)=(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)(→pp¯)K+ and B+→ψ(3770)(→pp¯)K+ are seen, and the 95% confidence level upper limits on their relative branching ratios are found to be RX(3872)<0.25×10−2 and Rψ(3770)<0.10 . In addition, the mass differences between the ηc(1S) and the J/ψ states, between the ηc(2S) and the ψ(2S) states, and the natural width of the ηc(1S) are measured as MJ/ψ−Mηc(1S)=110.2±0.5±0.9 MeV,Mψ(2S)−Mηc(2S)=52.5±1.7±0.6 MeV,Γηc(1S)=34.0±1.9±1.3 MeV.