First evidence for the two-body charmless baryonic decay $B^0 \to p \bar{p}$

TL;DR

This paper reports the first evidence for the rare two-body charmless baryonic decay of B^0 to p p̄, using LHCb data, with a 3.3 sigma significance, and sets new limits on B_s^0 decay.

Contribution

It provides the first experimental evidence for the B^0 → p p̄ decay and improves the upper bounds on B_s^0 → p p̄ decay by three orders of magnitude.

Findings

Evidence for B^0 → p p̄ with 3.3 sigma significance.

Measured branching fraction for B^0 → p p̄: (1.47^{+0.62}_{-0.51} ± 0.35)×10^{-8}.

No significant B_s^0 → p p̄ signal observed, setting stricter upper limits.

Abstract

The results of a search for the rare two-body charmless baryonic decays $B^0 \to p \bar{p}$ and $B_s^0 \to p \bar{p}$ are reported. The analysis uses a data sample, corresponding to an integrated luminosity of 0.9 fb$^{-1}$, of $pp$ collision data collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. An excess of $B^0 \to p \bar{p}$ candidates with respect to background expectations is seen with a statistical significance of 3.3 standard deviations. This is the first evidence for a two-body charmless baryonic $B^0$ decay. No significant $B_s^0 \to p \bar{p}$ signal is observed, leading to an improvement of three orders of magnitude over previous bounds. If the excess events are interpreted as signal, the 68.3% confidence level intervals on the branching fractions are {eqnarray} \cal{B}(B^0 \to p \bar{p}) & = & (1.47 \,^{+0.62}_{-0.51} \,^{+0.35}_{-0.14}) \times 10^{-8} \,, *{0.3cm} \cal{B}(B_s^0 \to p \bar{p}) & = & (2.84 \,^{+2.03}_{-1.68} \,^{+0.85}_{-0.18}) \times 10^{-8} \,, {eqnarray} where the first uncertainty is statistical and the second is systematic.