Measurement of $CP$ asymmetries in $\Lambda_b^0\to ph^{-}$ decays

TL;DR

This paper reports the most precise measurements of $CP$ asymmetries in $mbda_b^0$ decays to $pK^-$ and $p\u2208$ final states, using extensive LHCb data from Run 1 and Run 2, with improved systematic uncertainty evaluation.

Contribution

It provides the first combined analysis of Run 1 and Run 2 data with enhanced systematic uncertainty control, yielding the most precise $CP$ asymmetry measurements in these decay modes.

Findings

Measured $A_{CP}^{pK^-}$ as -1.1% with uncertainties

Measured $A_{CP}^{p\u2208}$ as 0.2% with uncertainties

Results are consistent with no $CP$ violation within uncertainties

Abstract

A search for $CP$ violation in $\Lambda_b^0\rightarrow pK^-$ and $\Lambda_b^0\rightarrow p\pi^-$ decays is presented using the full Run 1 and Run 2 data samples of $pp$ collisions collected with the LHCb detector, corresponding to an integrated luminosity of 9 $\mathrm{fb}^{-1}$ at center-of-mass energies of 7, 8, and 13 TeV. For the Run 2 data sample, the $CP$-violating asymmetries are measured to be $A_{CP}^{pK^-} = (-1.4 \pm 0.7 \pm 0.4)\%$ and $A_{CP}^{p\pi^-} = (0.4 \pm 0.9 \pm 0.4)\%$, where the first uncertainty is statistical and the second is systematic. Following significant improvements in the evaluation of systematic uncertainties compared to the previous LHCb measurement, the Run 1 dataset is reanalyzed to update the corresponding results. When combining the Run 2 and updated Run 1 measurements, the final results are found to be $A_{CP}^{pK^-} = (-1.1 \pm 0.7 \pm 0.4)\%$ and $A_{CP}^{p\pi^-} = (0.2 \pm 0.8 \pm 0.4)\%$, constituting the most precise measurements of these asymmetries to date.