Collision Energy Dependence of Hypertriton Production in Au+Au Collisions at RHIC

TL;DR

This study measures hypertriton production in gold-gold collisions across various energies, revealing energy-dependent yields and ratios that challenge thermal model predictions and suggest suppressed formation due to weak hyperon-nucleon interactions.

Contribution

First comprehensive energy-dependent measurement of hypertriton yields and ratios in heavy-ion collisions, providing new insights into hypernuclear formation mechanisms.

Findings

Hypertriton yields increase as collision energy decreases.

Yields are about half of thermal model predictions.

The hypertriton to lambda ratio remains constant across energies.

Abstract

The STAR Collaboration reports measurements of the collision energy dependence of hypertriton (${}^{3}_{\Lambda}$H) transverse momentum spectra and $p_{\rm T}$-integrated yields at mid-rapidity ($|y|<$0.5) in Au+Au collisions at 11 collision energies between 3.2 and 27\,GeV. The measured ${}^{3}_{\Lambda}$H yields and ${}^{3}_{\Lambda}$H/$\Lambda$ yields ratio in central collisions increase strongly with decreasing collision energy, and are a factor of $\sim$2 lower than thermal model predictions at this energy range. The mean $p_{\rm T}$ of ${}^{3}_{\Lambda}$H is lower than the Blast-Wave expectation using the freeze-out parameters from light hadrons. Furthermore, the observed double ratio $({}^{3}_{\Lambda}{\rm{H}}/\Lambda)/(t/p)$ maintains a constant value of $\sim$0.4 across the measured energy range. Within the coalescence framework, this ratio directly reflects the significantly suppressed formation probability of the weakly-bound hypertriton relative to the triton, which results from the weaker hyperon-nucleon interaction compared with the nucleon-nucleon interaction.