Formation and lifetime measurements of light hypernuclei in Ag+Ag collisions at $\sqrt{{\mathrm{s}}_{\mathrm{NN}}}$ = 2.55 GeV

Abstract

We present the first observation of ${}_{\hat{\mathrm{I}}}^3›\mathrm{H}$ and ${}_{\hat{\mathrm{I}}}^4›\mathrm{H}$ in Ag+Ag collisions at $\sqrt{{\mathrm{s}}_{\mathrm{NN}}}$ = 2.55 GeV, emitted around mid-rapidity. The hypernuclei are reconstructed via their two-body decay channels and identified through their weak-decay topology, employing an artificial neural network for enhanced discrimination. The analysis methodology is validated using $\hat{I}›$ hyperons. The resulting rapidity distributions, dN/dy, exhibit a bell shape centered at mid-rapidity. The yield of ${}_{\hat{\mathrm{I}}}^4›\mathrm{H}$ is equal to or exceeds that of ${}_{\hat{\mathrm{I}}}^3›\mathrm{H}$, which contrasts the measurement from the STAR collaboration at $\sqrt{{\mathrm{s}}_{\mathrm{NN}}}$ = 3 GeV and is consistent with a scenario in which hypernuclei receive feed-down from excited states. The data enable a high-precision measurement of the hypernuclei lifetimes. For the ${}_{\hat{\mathrm{I}}}^3›\mathrm{H}$, a lifetime of $\ddot{\mathrm{I}}{„}_{{}_{\hat{\mathrm{I}}}^3›\mathrm{H}}$ = $(239\pm 23(\mathrm{stat})\pm 18(\mathrm{sys}))\mathrm{ps}$, is extracted, consistent on the 1$\ddot{I}ƒ$ level with that of the free $\hat{I}›$. In contrast, the ${}_{\hat{\mathrm{I}}}^4›\mathrm{H}$ lifetime of $\ddot{\mathrm{I}}{„}_{{}_{\hat{\mathrm{I}}}^4›\mathrm{H}}$ = $(209\pm 7(\mathrm{stat})\pm 10(\mathrm{sys}))\mathrm{ps}$, shows a 4.5 $\ddot{I}ƒ$ deviation from the free $\hat{I}›$ lifetime. The results consolidate the available world data.

HADES collaboration