# First observation of the rare purely baryonic decay $B^0 \to p \bar{p}$

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## Abstract

The first observation of the decay of a $B^0$ meson to a purely baryonic final state, $B^0 \to p \bar{p}$, is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb$^{-1}$. The branching fraction is determined to be $${\cal B}(B^0 \to p \bar{p}) = ( 1.25 \pm 0.27 \pm 0.18 ) \times 10^{-8} ,$$ where the first uncertainty is statistical and the second systematic. The decay mode $B^0 \to p \bar{p}$ is the rarest decay of the $B^0$ meson observed to date. The decay $B_s^0 \to p \bar{p}$ is also investigated. No signal is seen and the upper limit ${\cal B}(B_s^0 \to p \bar{p}) < 1.5 \times 10^{-8}$ at 90% confidence level is set on the branching fraction.

## Figures and captions

 Invariant mass distribution of $p \overline p$ candidates. The fit result (blue, solid line) is shown together with each fit model component: the $B ^0 \rightarrow p \overline p$ signal (red, dashed line), the $B ^0_ s \rightarrow p \overline p$ signal (grey, dashed line) and the combinatorial background (green, dotted line). Fig1.pdf [89 KiB] HiDef png [236 KiB] Thumbnail [183 KiB] *.C file Invariant mass distribution of $K ^\pm \pi ^\mp$ candidates. The fit result (blue, solid line) is shown together with each fit model component. Fig2.pdf [169 KiB] HiDef png [338 KiB] Thumbnail [234 KiB] *.C file Animated gif made out of all figures. PAPER-2017-022.gif Thumbnail

## Supplementary Material [file]

 Supplementary material full pdf supple[..].pdf [249 KiB] This ZIP file contains supplementary material for the publication LHCb-PAPER-2017-022. The files are: - The PDF file with the supplementary material itself. - All figures in numerous formats. Fig3.pdf [146 KiB] HiDef png [249 KiB] Thumbnail [188 KiB] *C file Fig4.pdf [14 KiB] HiDef png [135 KiB] Thumbnail [106 KiB] *C file

Created on 22 October 2019.