Observation of Directed Flow of Hypernuclei $^3_{\Lambda}$H and $^4_{\Lambda}$H in $\sqrt{s_{\rm NN}}$ = 3 GeV Au+Au Collisions at RHIC

TL;DR

This paper reports the first observation of directed flow of hypernuclei $^3_{\Lambda}$H and $^4_{\Lambda}$H in 3 GeV Au+Au collisions at RHIC, revealing baryon number scaling and supporting coalescence as the production mechanism.

Contribution

It provides the first measurement of hypernuclei directed flow at this energy, demonstrating baryon number scaling and insights into their production mechanism.

Findings

Hypernuclei exhibit significant directed flow.

Directed flow follows baryon number scaling.

Supports coalescence as the dominant production mechanism.

Abstract

We report here the first observation of directed flow ($v_1$) of the hypernuclei $^3_{\Lambda}$H and $^4_{\Lambda}$H in mid-central Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 3 GeV at RHIC. These data are taken as part of the beam energy scan program carried out by the STAR experiment. From 165 $\times$ 10$^{6}$ events in 5%-40% centrality, about 8400 $^3_{\Lambda}$H and 5200 $^4_{\Lambda}$H candidates are reconstructed through two- and three-body decay channels. We observe that these hypernuclei exhibit significant directed flow. Comparing to that of light nuclei, it is found that the midrapidity $v_1$ slopes of $^3_{\Lambda}$H and $^4_{\Lambda}$H follow baryon number scaling, implying that the coalescence is the dominant mechanism for these hypernuclei production in such collisions.