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

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.