Beam Energy Dependence of Triton Production and Yield Ratio (${\mathrm{N}}_t\times {\mathrm{N}}_p/{\mathrm{N}}_d^2$) in Au+Au Collisions at RHIC

Abstract

We report the triton ($t$) production in mid-rapidity ($|y|<$ 0.5) Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$= 7.7--200 GeV measured by the STAR experiment from the first phase of the beam energy scan at the Relativistic Heavy Ion Collider (RHIC). The nuclear compound yield ratio (${\mathrm{N}}_t\times {\mathrm{N}}_p/{\mathrm{N}}_d^2$), which is predicted to be sensitive to the fluctuation of local neutron density, is observed to decrease monotonically with increasing charged-particle multiplicity ($d{N}_{ch}/d\eta$) and follows a scaling behavior. The $d{N}_{ch}/d\eta$ dependence of the yield ratio is compared to calculations from coalescence and thermal models. Enhancements in the yield ratios relative to the coalescence baseline are observed in the 0\%-10\% most central collisions at 19.6 and 27 GeV, with a significance of 2.3$\sigma$ and 3.4$\sigma$, respectively, giving a combined significance of 4.1$\sigma$. The enhancements are not observed in peripheral collisions or model calculations without critical fluctuation, and decreases with a smaller $p_T$ acceptance. The physics implications of these results on the QCD phase structure and the production mechanism of light nuclei in heavy-ion collisions are discussed.

6 pages, 4 figures, Supplemental Material: http://link.aps.org/supplemental/10.1103/PhysRevLett.130.202301

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