Observation of $B_{\mathbf{(}s\mathbf{)}}^0\to J/\psi p\overline{p}$ Decays and Precision Measurements of the $B_{\mathbf{(}s\mathbf{)}}^0$ Masses

The first observation of the decays $B_{(s)}^0\to J/\psi p\overline{p}$ is reported, using proton-proton collision data corresponding to an integrated luminosity of $5.2{\mathrm{fb}}^{-1}$, collected with the LHCb detector. These decays are suppressed due to limited available phase space, as well as due to Okubo-Zweig-Iizuka or Cabibbo suppression. The measured branching fractions are $\mathcal{B}(B^0\to J/\psi p\overline{p})=[4.51\pm 0.40(\text{stat})\pm 0.44(\text{syst})]\times {10}^{-7}$, $\mathcal{B}(B_s^0\to J/\psi p\overline{p})=[3.58\pm 0.19(\text{stat})\pm 0.39(\text{syst})]\times {10}^{-6}$. For the $B_s^0$ meson, the result is much higher than the expected value of $\mathcal{O}({10}^{-9})$. The small available phase space in these decays also allows for the most precise single measurement of both the $B^0$ mass as $5279.74\pm 0.30(\text{stat})\pm 0.10(\text{syst})\mathrm{MeV}$ and the $B_s^0$ mass as $5366.85\pm 0.19(\text{stat})\pm 0.13(\text{syst})\mathrm{MeV}$.

Figure 1

Leading Feynman diagrams for (a) $B^0\to J/\psi p\overline{p}$ and (b) $B_s^0\to J/\psi p\overline{p}$ decays.

Figure 2

Fit to the $J/\psi p\overline{p}$ invariant-mass distribution of the $B_{(s)}^0$ signal modes.