Beam-Energy Dependence of the Directed Flow of Deuterons in Au+Au Collisions

TL;DR

This study measures the directed flow of deuterons in gold-gold collisions across various energies, revealing a unique energy dependence and differences from protons, with implications for understanding baryon density effects.

Contribution

It provides the first detailed measurement of deuteron directed flow across multiple energies, highlighting differences from proton flow and informing models of heavy-ion collisions.

Findings

Deuteron $v_1(y)$ slope is near zero at high energies but shows enhancement at 7.7 GeV.

Proton $v_1(y)$ slopes are generally negative above 10 GeV.

Results are compared with transport and coalescence models.

Abstract

We present a measurement of the first-order azimuthal anisotropy, $v_1(y)$, of deuterons from Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV recorded with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The energy dependence of the $v_1(y)$ slope, $dv_{1}/dy|_{y=0}$, for deuterons, where $y$ is the rapidity, is extracted for semi-central collisions (10-40\% centrality) and compared to that of protons. While the $v_1(y)$ slopes of protons are generally negative for $\sqrt{s_{NN}} >$ 10 GeV, those for deuterons are consistent with zero, a strong enhancement of the $v_1(y)$ slope of deuterons is seen at the lowest collision energy (the largest baryon density) at $\sqrt{s_{NN}} =$ 7.7 GeV. In addition, we report the transverse momentum dependence of $v_1$ for protons and deuterons. The experimental results are compared with transport and coalescence models.