Measurement of hadron suppression and study of its connection with vanishing $v_{\mathrm{3}}$ at low $\sqrt{s_{\mathrm{NN}}}$ in Au+Au collisions with STAR

TL;DR

This study investigates hadron suppression and triangular flow ($v_3$) in Au+Au collisions across a range of energies at RHIC, providing evidence for QGP formation at lower energies through suppression patterns and flow measurements.

Contribution

It presents new measurements of hadron suppression and $v_3$ at energies down to 7.7 GeV, exploring the QGP signatures and their energy dependence in the RHIC Beam Energy Scan.

Findings

Hadron suppression persists down to 14.5 GeV at certain centralities.

$v_3$ disappears below 14.5 GeV for small systems but persists in larger systems.

Evidence suggests QGP formation at lower collision energies.

Abstract

At top RHIC and LHC energies the suppression of high transverse momentum ($p_{\mathrm{T}}$) hadrons provides evidence for partonic energy loss in QGP. We study partonic energy loss in the RHIC Beam Energy Scan (BES) by investigating the centrality dependence of the binary-collision-scaled high-$p_{\mathrm{T}}$ yields. Observing a decrease of the scaled yield in more central collisions is proposed as a possible signature for jet quenching. Even at energies and centralities where this signature is lost a QGP may still be formed since competing phenomena responsible for enhancements may overwhelm the suppression from energy loss. Measurements in several ranges of $p_{\mathrm{T}}$ from $\sqrt{s_{_{\mathrm{NN}}}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV data show that relative hadron suppression persists at least down to 14.5 GeV. To further investigate both the possible formation of a QGP at these lower energies and whether the observed hadron suppression coincides with the onset of other QGP signatures, we examine the energy and centrality dependence of $v_{3}$. Models have shown that the development of $v_{3}$ requires the presence of a low viscosity phase early in the collision. We find that for collisions with $N_{\mathrm{part}}$<50, $v_{3}$ disappears for energies below 14.5 GeV, suggestive of a turn-off of the QGP. But for $N_{\mathrm{part}}$>50, $v_{3}$ persists down to the lowest energies. Together, these signatures provide possible evidence for the formation of a QGP in the lowest energy collisions at RHIC.