# Observation of $B^0_{(s)} \to J/\psi p \overline{p}$ decays and precision measurements of the $B^0_{(s)}$ masses

## TL;DR

This paper reports the first observation of specific rare B meson decays into J/psi and proton-antiproton pairs, along with precise measurements of their masses, revealing unexpectedly high branching fractions for B_s decays.

## Contribution

The study provides the first observation of $B^0_{(s)} o J/ heta p ar{p}$ decays and offers the most precise measurements of $B^0$ and $B_s$ meson masses to date.

## Key findings

- First observation of $B^0_{(s)} o J/ heta p ar{p}$ decays.
- Measured branching fractions are significantly higher than theoretical expectations for $B_s$ decays.
- Achieved the most precise measurements of $B^0$ and $B_s$ meson masses.

## Abstract

The first observation of the decays $B^0_{(s)} \to J/\psi p \overline{p}$ is reported, using proton-proton collision data corresponding to an integrated luminosity of $5.2{\text{\,fb}}^{-1}$, collected with the \mbox{LHCb}\xspace 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 \begin{align*} \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^0_s \to J/\psi p \overline{p}) &= (3.58\pm 0.19\; \text{(stat)} \pm 0.39\; \text{(syst)}) \times 10^{-6}. \end{align*} For the $B^0_s$ meson, the result is much higher than the expected value of $ {\cal 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 ${5279.74 \pm 0.30\; ({\rm stat})\pm 0.10\; ({\rm syst})}$ MeV, and the $B^0_s$ mass as ${5366.85 \pm 0.19\; ({\rm stat})\pm 0.13\; ({\rm syst})}$ MeV.