Observation of the rare baryonic decay $B^{+}\rightarrow p \bar{\it{\Lambda}}$ and measurement of its weak decay parameter

TL;DR

This paper reports the first observation of the rare baryonic decay $B^{+}\rightarrow p \bar{\Lambda}$, measuring its branching fraction and decay parameter, providing new insights into baryonic B-meson decays at high-energy colliders.

Contribution

The study presents the first observation and measurement of the decay $B^{+}\rightarrow p \bar{\Lambda}$, including its branching fraction and decay parameter, using LHCb data from 2016-2018.

Findings

Decay $B^{+}\rightarrow p \bar{\Lambda}$ observed with >7 sigma significance.

Branching fraction measured as $(1.24\pm 0.17\pm 0.05\pm 0.03)\times 10^{-7}$.

Decay parameter $\alpha_B$ measured to be approximately 0.87.

Abstract

The first observation of the decay $B^{+}\rightarrow p \bar{\it{\Lambda}}$ is presented, using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4\,\mathrm{fb}^{-1}$. The signal significance exceeds seven standard deviations. Using the $B^{+} \rightarrow K^{\mathrm{0}}_{\mathrm{S}} \pi^{+}$ decay as a normalization channel, the branching fraction is measured and combined with previous LHCb results based on data collected at 7 and 8 TeV in 2011 and 2012, yielding $\mathcal{B}(B^{+}\rightarrow p \bar{\it{\Lambda}})=(1.24\pm 0.17\pm 0.05\pm 0.03)\times 10^{-7}$, where the first uncertainty is statistical, the second is systematic, and the third comes from the uncertainty on the branching fraction of the normalization channel. The $B^{+}\rightarrow p \bar{\it{\Lambda}}$ weak decay parameter is measured to be $\alpha_B = 0.87_{-0.29}^{+0.26} \pm 0.09$, indicating the presence of comparable S-wave and P-wave decay amplitudes.