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New Hypernuclei Measurements from STAR

Yingjie Zhou

Abstract

Hypernuclei are bound states of hyperons (Y) and nucleons (N). Measurements on their yields can help us investigate their production mechanisms. In particular, the ${}^5_Λ$He and $^{4}_Λ$H(e) are substantially tighter bound compared to the $^{3}_Λ$H. The large radius of the $^{3}_Λ$H leads to suppression in coalescence models, but not in the thermal model where the size of the nucleus does not play a role. As such, studying the $A=3$--5 hypernuclei yields allow us to extract information on the effects of hypernuclear binding on hypernuclei production in heavy-ion collisions. In these proceedings, we present measurements of ${}^5_Λ$He yields in Au+Au collisions at $\sqrt{s_{\rm NN}}=3.0$ GeV, $^{4}_Λ$H(e) yields in Au+Au collisions at $\sqrt{s_{\rm NN}}=3.0$--$4.5$ GeV, and $^{3}_Λ$H yields in Au+Au collisions at $\sqrt{s_{\rm NN}}=3$--$27$ GeV. Results on the directed flow of hypernuclei are also reported. The physics implications of these measurements are discussed.

New Hypernuclei Measurements from STAR

Abstract

Hypernuclei are bound states of hyperons (Y) and nucleons (N). Measurements on their yields can help us investigate their production mechanisms. In particular, the He and H(e) are substantially tighter bound compared to the H. The large radius of the H leads to suppression in coalescence models, but not in the thermal model where the size of the nucleus does not play a role. As such, studying the --5 hypernuclei yields allow us to extract information on the effects of hypernuclear binding on hypernuclei production in heavy-ion collisions. In these proceedings, we present measurements of He yields in Au+Au collisions at GeV, H(e) yields in Au+Au collisions at -- GeV, and H yields in Au+Au collisions at -- GeV. Results on the directed flow of hypernuclei are also reported. The physics implications of these measurements are discussed.
Paper Structure (7 sections, 4 figures)

This paper contains 7 sections, 4 figures.

Table of Contents

  1. Introduction
  2. STAR Beam Energy Scan II and hypernuclei reconstruction
  3. Results and Discussion
  4. Particle Yields
  5. Collectivity
  6. Summary
  7. Acknowledgement

Figures (4)

  • Figure 1: Rapidity yield distributions of hypernuclei ${}^{3}_{\Lambda}\mathrm{H}$, ${}^{4}_{\Lambda}\mathrm{H}$, ${}^{4}_{\Lambda}\mathrm{He}$ at $\sqrt{s_{\rm NN}}=3.5$ GeV, and ${}^{5}_{\Lambda}\mathrm{He}$ at $\sqrt{s_{\rm NN}}=3.0$ GeV in 0--40% Au+Au collisions.
  • Figure 2: Left: Measured mid-rapdity yields of light (hyper)nuclei in Au+Au collisions at $\sqrt{s_{\rm NN}}=3.0$ GeV, scaled by their spin degeneracy factor $(2J+1)$, as a function of mass number $A$, compared to thermal model calculations. Right: Comparison of measured and thermal model predicted yields for $^5_\Lambda$He, including contributions from unstable nuclei. Data from STAR:2023uxkSTAR:2024zncSTAR:2021orx.
  • Figure 3: Left: Mass dependence of the mid-rapidity $\langle p_\mathrm{T} \rangle$ for light (hyper)nuclei from $\sqrt{s_{\rm NN}} = 3.0$ GeV in 0--40% Au+Au collisions. The symbols represent measurements, while the lines represent hydrodynamic-inspired Blast-Wave model calculations. The gray line shows the prediction using proton freeze-out parameters, while the red line shows the prediction using $\Lambda$ parameters. Right: Directed flow slope $dv_{1}/dy$ at mid-rapidity for light (hyper)nuclei as a function of mass number in $\sqrt{s_{\rm NN}}=3.0$ GeV 5--40% Au+Au collisions. Black and red bands indicate linear fits to the light (hyper)nuclei, respectively.
  • Figure :