# Observation of $\eta_c(2S) \to p\overline{p}$ and search for X(3872) $\to p\overline{p}$ decays

LHCb Collaboration; Bernet, R; Müller, K; Serra, N; Steinkamp, O; Straumann, U; Vollhardt, A; et al (2017). Observation of $\eta_c(2S) \to p\overline{p}$ and search for X(3872) $\to p\overline{p}$ decays. Physics Letters B, B769:305-313.

## Abstract

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 $3.0\rm \, fb^{-1}$ 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 $B^{+} \to [c\bar c] K^{+}$. The product of branching fractions normalised to that for the $J/\psi$ intermediate state, $\mathcal{R}_{\eta_{c}(2S)}$, is measured to be $\mathcal{R}_{\eta_{c}(2S)}\equiv\frac{\mathcal{B}(B^+ \to \eta_{c}(2S) K^{+}) \times \mathcal{B}(\eta_c(2S) \to p\overline{p})}{\mathcal{B}(B^{+} \to J/\psi K^{+}) \times \mathcal{B}(J/\psi\to p\overline{p})} = (1.58 \pm 0.33 \pm 0.09)\times 10^{-2}$,
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 ${\cal R}_{X(3872)}<0.25\times10^{-2}$ 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
$M_{J/\psi} - M_{\eta_{c}(1S)} = 110.2 \pm 0.5 \pm 0.9 MeV$,
$M_{\psi(2S)} - M_{\eta_{c}(2S)} = 52.5 \pm 1.7 \pm 0.6 MeV$,
$\Gamma_{\eta_{c}(1S)} = 34.0 \pm 1.9 \pm 1.3 MeV$.

## Abstract

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 $3.0\rm \, fb^{-1}$ 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 $B^{+} \to [c\bar c] K^{+}$. The product of branching fractions normalised to that for the $J/\psi$ intermediate state, $\mathcal{R}_{\eta_{c}(2S)}$, is measured to be $\mathcal{R}_{\eta_{c}(2S)}\equiv\frac{\mathcal{B}(B^+ \to \eta_{c}(2S) K^{+}) \times \mathcal{B}(\eta_c(2S) \to p\overline{p})}{\mathcal{B}(B^{+} \to J/\psi K^{+}) \times \mathcal{B}(J/\psi\to p\overline{p})} = (1.58 \pm 0.33 \pm 0.09)\times 10^{-2}$,
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 ${\cal R}_{X(3872)}<0.25\times10^{-2}$ 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
$M_{J/\psi} - M_{\eta_{c}(1S)} = 110.2 \pm 0.5 \pm 0.9 MeV$,
$M_{\psi(2S)} - M_{\eta_{c}(2S)} = 52.5 \pm 1.7 \pm 0.6 MeV$,
$\Gamma_{\eta_{c}(1S)} = 34.0 \pm 1.9 \pm 1.3 MeV$.

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