Measurement of the lifetime and $Λ$ separation energy of $^{3}_Λ\mathrm H$

The most precise measurements to date of the $^{3}_{\Lambda}\mathrm H$ lifetime $\tau$ and $\Lambda$ separation energy ${\rm B}_{\Lambda}$ are obtained using the data sample of Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV collected by ALICE at the LHC. The $^{3}_{\Lambda}\mathrm H$ is reconstructed via its charged two-body mesonic decay channel ($^{3}_{\Lambda}\mathrm{H} \rightarrow$ $^3$He + $\pi^-$ and the charge-conjugate process). The measured values $\tau = [253 \pm 11 \text{ (stat.)} \pm 6 \text{ (syst.)}]$ ps and ${\rm B}_{\Lambda}= [72 \pm 63 \text{ (stat.)} \pm 35 \text{ (syst.)}]$ keV are compatible with predictions from effective field theories and conclusively confirm that the $^{3}_{\Lambda}\mathrm H$ is a weakly-bound system.


Submitted to: PRL
e-Print: arXiv:2209.07360 | PDF | inSPIRE
Figure group

Figure 1

Invariant-mass distribution of the selected $\Hee + \pi^{-}$ and charge conjugate pairs. Vertical lines represent the statistical Poisson-distributed uncertainties. A two component model is fitted to the invariant-mass spectrum: the blue line represents the total fit while the orange dashed line shows the background component only..

Figure 2

Left: exponential decay spectrum as a function of the proper decay length for \hyp, the blue points represent the measured yield, while the orange line represents the best fit to the measurement. Right: \BL measurement as a function of the proper decay length. Only statistical uncertainties are shown, see the text for a description of the determination of the systematic uncertainties. The fit probability computed with a Pearson test is reported..

Figure 3

The \hyp lifetime relative to the free $\Lambda$ lifetime as a function of the \BL for pionless EFT  (red), $\chi$EFT  (orange), and the original $\pi$ exchange calculations  (magenta). The blue point represents the measurement presented in this Letter with the statistical and systematic uncertainties depicted with lines and box, respectively..

Figure 4

Collection of the \hyp lifetime (left) and \BL (right) measurements obtained with different experimental techniques. Thehorizontal lines and boxes are the statistical and systematic uncertainties respectively. The dashed-dotted lines are the corresponding theoretical predictions..