Measurement of the $Λ$ hyperon lifetime

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


Phys. Rev. D 108 (2023) 032009
HEP Data
e-Print: arXiv:2303.00606 | PDF | inSPIRE
Figure group

Figure 1

Invariant mass spectra of p$\pi$ pairs measured in central collisions (0--10$\%$) at low (left) and large (right) $L_{\rm proper}$. The green area indicates the peak region.

Figure 2

Reconstruction efficiency of primary $\Lambda$ ($\overline{\Lambda}$) (left) and fraction of secondary $\Lambda$ ($\overline{\Lambda}$) (right) in central Pb--Pb collisions (0--10$\%$).

Figure 3

$L_{\rm proper}$ spectra of $\Lambda$ (left), $\overline{\Lambda}$ (middle) and their sum (right), and exponential fits for the lifetime extractions. Only statistical uncertainties are shown for each data point and for the mean lifetime extracted from the exponential fit.

Figure 4

$\Lambda$ lifetime measured in different centrality intervals. Only statistical uncertainties are shown.

Figure 5

ALICE measurement of the $\Lambda$ lifetime in comparison with previous measurements and the current world average taken from the PDG . Statistical and systematic uncertainties are added in quadrature.