Measurement of the Λ hyperon lifetime

Abstract

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