Precision Studies and Searches for CP Asymmetries in the Inclusive Decay $\Lambda_{c}^{+}\to \Lambda X$

TL;DR

This study measures the polarization of Lambda hyperons in inclusive Lambda_c+ decays, searches for CP violation, and updates the branching fraction with improved precision, finding no evidence of CP violation.

Contribution

First measurement of Lambda polarization in inclusive Lambda_c+ decays, along with a CP violation search and an improved branching fraction measurement.

Findings

Lambda polarization measured as -0.393 and 0.288 for Lambda and anti-Lambda.

CP asymmetry consistent with zero within uncertainties.

Branching fraction of 38.07% with fourfold improved precision.

Abstract

Based on $e^+e^-$ annihilation data collected with the BESIII detector at center-of-mass energies from 4.600 to 4.699 GeV, corresponding to an integrated luminosity of 4.5 fb$^{-1}$, we present the first measurement of the longitudinal polarization of $\Lambda$ hyperons produced in the inclusive decay $\Lambda_c^+ \to \Lambda X$, where $X$ denotes any allowed final state. The polarizations are determined to be $\mathcal{P}_{\Lambda} = -0.393 \pm 0.055_{\mathrm{sta.}} \pm 0.020_{\mathrm{sys.}}$ and $\mathcal{P}_{\bar{\Lambda}} = 0.288 \pm 0.056_{\mathrm{sta.}} \pm 0.017_{\mathrm{sys.}}$. We then search for CP violation using an asymmetry constructed from the $\Lambda$ polarization and the $\Lambda \to p \pi^-$ decay asymmetry parameters, and obtain $\mathcal{A}_{\mathrm{CP}}^{\mathrm{pol}} = 0.15 \pm 0.12_{\mathrm{sta.}} \pm 0.04_{\mathrm{sys.}}$. We also perform an updated measurement of the absolute branching fraction, resulted as $\mathcal{B}(\Lambda_c^+ \to \Lambda X) = (38.07 \pm 0.38_{\mathrm{sta.}} \pm 0.49_{\mathrm{sys.}})\%$, with precision improved by a factor of four relative to the current world average. A search for direct CP violation yields $\mathcal{A}_{\mathrm{CP}}^{\mathrm{dir}} = (1.5 \pm 1.0_{\mathrm{sta.}} \pm 1.0_{\mathrm{sys.}})\%$. No evidence for CP violation in inclusive charm baryon decays is observed.