Beam Energy Dependence of the Third Harmonic of Azimuthal Correlations in Au+Au Collisions at RHIC

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We present results from a harmonic decomposition of two-particle azimuthal correlations measured with the STAR detector in $\mathrm{Au}+\mathrm{Au}$ collisions for energies ranging from $\sqrt{{s}_{NN}}=7.7$ to 200 GeV. The third harmonic ${v}_{3}^{2}{2}=⟨\mathrm{cos}3({\ensuremath{\phi}}_{1}\ensuremath{-}{\ensuremath{\phi}}_{2})⟩$, where ${\ensuremath{\phi}}_{1}\ensuremath{-}{\ensuremath{\phi}}_{2}$ is the angular difference in azimuth, is studied as a function of the pseudorapidity difference between particle pairs $\mathrm{\ensuremath{\Delta}}\ensuremath{\eta}={\ensuremath{\eta}}_{1}\ensuremath{-}{\ensuremath{\eta}}_{2}$. Nonzero ${v}_{3}^{2}{2}$ is directly related to the previously observed large-$\mathrm{\ensuremath{\Delta}}\ensuremath{\eta}$ narrow-$\mathrm{\ensuremath{\Delta}}\ensuremath{\phi}$ ridge correlations and has been shown in models to be sensitive to the existence of a low viscosity quark gluon plasma phase. For sufficiently central collisions, ${v}_{3}^{2}{2}$ persist down to an energy of 7.7 GeV, suggesting that quark gluon plasma may be created even in these low energy collisions. In peripheral collisions at these low energies, however, ${v}_{3}^{2}{2}$ is consistent with zero. When scaled by the pseudorapidity density of charged-particle multiplicity per participating nucleon pair, ${v}_{3}^{2}{2}$ for central collisions shows a minimum near $\sqrt{{s}_{NN}}=20\text{ }\text{ }\mathrm{GeV}$.

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