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 $eta_{c}(2S) to p bar p$ is reported using proton-proton collision data corresponding to an integrated luminosity of $3.0rm , fb^{-1}$ recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The $eta_{c}(2S)$ resonance is produced in the decay $B^{+} to [cbar c] K^{+}$. The product of branching fractions normalised to that for the $J/psi$ intermediate state, ${cal R}_{eta_{c}(2S)}$, is measured to be begin{align*} {cal R}_{eta_{c}(2S)}equivfrac{{mathcal B}(B^{+} to eta_{c}(2S) K^{+}) times {mathcal B}(eta_{c}(2S) to p bar p)}{{mathcal B}(B^{+} to J/psi K^{+}) times {mathcal B}(J/psito p bar p)} =~& (1.58 pm 0.33 pm 0.09)times 10^{-2}, end{align*} where the first uncertainty is statistical and the second systematic. No signals for the decays $B^{+} to X(3872) (to p bar p) K^{+}$ and $B^{+} to psi(3770) (to p bar p) K^{+}$ are seen, and the 95% confidence level upper limits on their relative branching ratios are % found to be ${cal R}_{X(3872)}<0.25times10^{-2}$ and ${cal R}_{psi(3770))}<0.10$. In addition, the mass differences between the $eta_{c}(1S)$ and the $J/psi$ states, between the $eta_{c}(2S)$ and the $psi(2S)$ states, and the natural width of the $eta_{c}(1S)$ are measured as begin{align*} M_{J/psi} - M_{eta_{c}(1S)} =~& 110.2 pm 0.5 pm 0.9 rm , MeV, M_{psi(2S)} -M_{eta_{c}(2S)} =~ & 52.5 pm 1.7 pm 0.6 rm , MeV, Gamma_{eta_{c}(1S)} =~& 34.0 pm 1.9 pm 1.3 rm , MeV. end{align*}