Evidence for the strangeness-changing weak decay $\Xi_b^-\to\Lambda_b^0\pi^-$

TL;DR

This paper reports the first evidence for the weak decay of a $ ext{Xi}_b^-$ baryon into a $ ext{Lambda}_b^0$ baryon and a pion, using LHCb data, with a significance of 3.2 sigma and an estimated branching fraction.

Contribution

The first search and evidence for the strangeness-changing weak decay $ ext{Xi}_b^- o ext{Lambda}_b^0 ext{pi}^-$ using LHCb data, providing the decay's relative rate and branching fraction estimates.

Findings

Evidence for the decay with 3.2 sigma significance.

Measured relative rate: (5.7±1.8+0.8-0.9)×10^{-4}.

Estimated branching fraction range: 0.19% to 0.57%.

Abstract

Using a $pp$ collision data sample corresponding to an integrated luminosity of 3.0~fb$^{-1}$, collected by the LHCb detector, we present the first search for the strangeness-changing weak decay $\Xi_b^-\to\Lambda_b^0\pi^-$. No $b$ hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported. The relative rate is measured to be ${{f_{\Xi_b^-}}\over{f_{\Lambda_b^0}}}{\cal{B}}(\Xi_b^-\to\Lambda_b^0\pi^-) = (5.7\pm1.8^{+0.8}_{-0.9})\times10^{-4}$, where $f_{\Xi_b^-}$ and $f_{\Lambda_b^0}$ are the $b\to\Xi_b^-$ and $b\to\Lambda_b^0$ fragmentation fractions, and ${\cal{B}}(\Xi_b^-\to\Lambda_b^0\pi^-)$ is the branching fraction. Assuming $f_{\Xi_b^-}/f_{\Lambda_b^0}$ is bounded between 0.1 and 0.3, the branching fraction ${\cal{B}}(\Xi_b^-\to\Lambda_b^0\pi^-)$ would lie in the range from $(0.57\pm0.21)\%$ to $(0.19\pm0.07)\%$.