Beam Energy Dependence of Triton Production and Yield Ratio (${N}_{t}\ifmmode\times\else\texttimes\fi{}{N}_{p}/{N}_{d}^{2}$) in $\mathrm{Au}+\mathrm{Au}$ Collisions at RHIC

Beam Energy Dependence of Triton Production and Yield Ratio ( $N_{t} \times N_{p} / N_{d}^{2}$ ) in $Au + Au$ Collisions at RHIC

M. I. Abdulhamid et al. (STAR Collaboration)

Phys. Rev. Lett. 130, 202301 – Published 16 May 2023

Abstract

We report the triton ( $t$ ) production in midrapidity ( $| y | < 0.5$ ) $Au + Au$ collisions at $\sqrt{s_{N N}} = 7.7 - 200 GeV$ measured by the STAR experiment from the first phase of the beam energy scan at the Relativistic Heavy Ion Collider. The nuclear compound yield ratio ( $N_{t} \times N_{p} / N_{d}^{2}$ ), which is predicted to be sensitive to the fluctuation of local neutron density, is observed to decrease monotonically with increasing charged-particle multiplicity ( $d N_{c h} / d η$ ) and follows a scaling behavior. The $d N_{c h} / d η$ 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 $2.3 σ$ and $3.4 σ$ , respectively, giving a combined significance of $4.1 σ$ . 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.

Received 20 September 2022
Revised 21 February 2023
Accepted 30 March 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.202301

Physics Subject Headings (PhySH)

Relativistic heavy-ion collisions

Nuclear Physics

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Vol. 130, Iss. 20 — 19 May 2023

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Figure 1
Transverse momentum ( $p_{T}$ ) spectra for midrapidity ( $| y | < 0.5$ ) tritons from 0%–10%, 10%–20%, 20%–40%, and 40%–80% centralities in $Au + Au$ collisions at $\sqrt{s_{N N}} = 7.7$ , 11.5, 14.5, 19.6, 27, 39, 54.4, 62.4, and 200 GeV. Dashed lines are the corresponding Blast-Wave fits with the profile parameter $n = 1$ . The statistical and systematic uncertainties are shown as vertical lines and boxes, respectively.
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Figure 2
Collision energy dependence of the mid-rapidity ratios $N_{d} / N_{p}$ (blue solid squares) and $N_{t} / N_{p}$ (red solid circles) from the top 0%–10% central $Au + Au$ collisions. Statistical and systematic uncertainties are shown as vertical lines and brackets, respectively. For comparison, results from FOPI [92], E864 [25], PHENIX [93, 94], and ALICE [28] are also shown. The lines are results from the thermal model using chemical freeze-out conditions from Refs. [96, 97].
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Figure 3
The yield ratio $N_{t} \times N_{p} / N_{d}^{2}$ as a function of charged-particle multiplicity $d N_{c h} / d η$ ( $| η | < 0.5$ ) in $Au + Au$ collisions at $\sqrt{s_{N N}} = 7.7$ —200 GeV for 0%–10%, 10%–20%, 20%–40%, and 40%–80% centralities. Statistical and systematic uncertainties are shown as vertical lines and brackets, respectively. The black dot-dashed line denotes the coalescence-inspired fit. The open diamond denotes the yield ratio of 0%–20% central $Au + Au$ collisions at $\sqrt{s_{N N}} = 54.4 GeV$ . The red shaded vertical band on the right side of the figure represents the multiplicity independent systematic uncertainties on these ratios. The significance of the deviation relative to the fit is shown in the lower panel. The results calculated from thermal model are shown as the blue long-dashed line. Calculations from AMPT and $MUSIC + UrQMD$ hybrid models [67, 68] are shown as shaded bands.
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Figure 4
Collision energy, centrality, and $p_{T}$ dependence of the yield ratio $N_{t} \times N_{p} / N_{d}^{2}$ in $Au + Au$ collisions at RHIC. Solid circles are the results from 0%–10% central (left panel) and 40%–80% peripheral (right panel) collisions. Colored bands in panel (a) denote $p_{T}$ acceptance dependence, for which the statistical and systematic uncertainties are added in quadrature. Red solid circles are the final results with extrapolation to the full $p_{T}$ range. Statistical and systematic uncertainties are shown as bars and brackets, respectively. Red vertical bands on the right side of panels represent the common systematic uncertainties. Dashed lines are the coalescence baselines obtained from the coalescence-inspired fit. Shaded areas denote the calculations from hadronic transport AMPT and $MUSIC + UrQMD$ hybrid models [68].
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Physical Review Letters

Beam Energy Dependence of Triton Production and Yield Ratio (Nt×Np/Nd2) in Au+Au Collisions at RHIC

M. I. Abdulhamid et al. (STAR Collaboration)

Phys. Rev. Lett. 130, 202301 – Published 16 May 2023

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Beam Energy Dependence of Triton Production and Yield Ratio ( $N_{t} \times N_{p} / N_{d}^{2}$ ) in $Au + Au$ Collisions at RHIC