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

Abstract

Based on $e^{+}{e}^{-}$ annihilation data collected with the BESIII detector at center-of-mass energies from $4.600$ to $4.699\mathrm{GeV}$, corresponding to an integrated luminosity of $4.5{\mathrm{fb}}^{-1}$, we present the first measurement of the longitudinal polarization of $\Lambda$ hyperon produced in the inclusive decay ${\Lambda }_c^{+}\to \Lambda X$, where $X$ denotes any allowed final states. The polarizations are determined to be $P_{\Lambda }=-0.393\pm 0.055_{\mathrm{stat}}\pm 0.020_{\mathrm{syst}}$ and $P_{\bar{\Lambda }}=0.288\pm 0.056_{\mathrm{stat}}\pm 0.017_{\mathrm{syst}}$. A search for CP violation is performed using an asymmetry constructed from the $\Lambda$ polarization and the $\Lambda \to p{\pi }^{-}$ decay asymmetry parameter, and $A_{\mathrm{CP}}^{\mathrm{pol}}=0.15\pm 0.12_{\mathrm{stat}}\pm 0.03_{\mathrm{syst}}$ was obtained. Furthermore, an updated measurement of the absolute branching fraction is reported as $B({\Lambda }_c^{+}\to \Lambda X)=(38.07\pm 0.38_{\mathrm{stat}}\pm 0.49_{\mathrm{syst}})\%$, representing a fourfold precision improvement over the previous BESIII measurement. A search for CP violation in the decay rate yields $A_{\mathrm{CP}}^{\mathrm{dir}}=(1.5\pm 1.0_{\mathrm{stat}}\pm 1.0_{\mathrm{syst}})\%$. No evidence for CP violation is observed in this inclusive charm baryon decay. The subscripts `stat' and `syst' denote statistical and systematic uncertainties, respectively.