Study of $\it{\Lambda}_{\it{b}}^\rm{0}$ and $\it{\Xi}_{\it{b}}^\rm{0}$ decays to $\it{\Lambda} h^+h^{'-}$ and evidence for $CP$ violation in $\it{\Lambda}_{\it{b}}^\rm{0}\to\it{\Lambda} K^+K^-$ decays

TL;DR

This paper reports the first observation of certain baryon decays, measures their branching fractions, and finds evidence of $CP$ violation in a specific decay mode using LHCb data, advancing understanding of matter-antimatter asymmetry.

Contribution

It introduces the first observation of $ ext{Lambda}_b^0$ and $ ext{Xi}_b^0$ decays to $ ext{Lambda} h^+ h'^-$ and provides evidence for $CP$ violation in $ ext{Lambda}_b^0 o ext{Lambda} K^+ K^-$ decays.

Findings

First observation of $ ext{Lambda}_b^0 o ext{Lambda} o ext{Lambda} ext{pi}^+$ and $ ext{Xi}_b^0 o ext{Lambda} K^- ext{pi}^+$ decays.

Evidence for $CP$ violation in $ ext{Lambda}_b^0 o ext{Lambda} K^+ K^-$ decay.

Measured $CP$ asymmetries are consistent with zero for other decay modes.

Abstract

A study of $\it{\Lambda}_{\it{b}}^\rm{0}$ and $\it{\Xi}_{\it{b}}^\rm{0}$ decays to $\it{\Lambda} h^{+} h^{\prime -}$ $(h^{(\prime)}=\pi, K)$ is performed using $pp$ collision data collected by the LHCb experiment during LHC Runs 1$-$2, corresponding to an integrated luminosity of $9~\rm{fb}^{-1}$. The branching fractions for these decays are measured using the $\it{\Lambda}_{\it{b}}^\rm{0}\to\it{\Lambda}_{\it{c}}^+(\to\it{\Lambda}\pi^+)\pi^-$ decay as control channel. The decays $\it{\Lambda}_{\it{b}}^\rm{0}\to\it{\Lambda}\pi^+\pi^-$ and $\it{\Xi}_{\it{b}}^\rm{0}\to\it{\Lambda}K^-\pi^+$ are observed for the first time. For decay modes with sufficient signal yields, $CP$ asymmetries are measured in the full and localized regions of the final-state phase space. Evidence is found for $CP$ violation in the $\it{\Lambda}_{\it{b}}^\rm{0}\to\it{\Lambda}K^+K^-$ decay, interpreted as originating primarily from an asymmetric $\it{\Lambda}_{\it{b}}^\rm{0} \to \it{N}^{*+} \it{K}^-$ decay amplitude. The measured $CP$ asymmetries for the other decays are compatible with zero.