Measurement of the $Λ$ hyperon lifetime

Abstract

A new, more precise measurement of the $Λ$ hyperon lifetime is performed using a large data sample of Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with ALICE. The $Λ$ and $\overlineΛ$ hyperons are reconstructed at midrapidity using their two-body weak decay channel $Λ\rightarrow \mathrm{p} + π^{-}$ and $\overlineΛ \rightarrow \overline{\mathrm{p}} + π^{+}$. The measured value of the $Λ$ lifetime is $τ_Λ = [261.07 \pm 0.37 \ ( \rm stat.) \pm 0.72 \ (\rm syst.) ]\ \rm ps$. The relative difference between the lifetime of $Λ$ and $\overlineΛ$, which represents an important test of CPT invariance in the strangeness sector, is also measured. The obtained value $(τ_Λ-τ_{\overlineΛ})/τ_Λ = 0.0013 \pm 0.0028 \ (\mathrm{stat.}) \pm 0.0021 \ (\mathrm{syst.})$ is consistent with zero within the uncertainties. Both measurements of the $Λ$ hyperon lifetime and of the relative difference between $τ_Λ$ and $τ_{\overlineΛ}$ are in agreement with the corresponding world averages of the Particle Data Group and about a factor of three more precise.