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

We present results from a harmonic decomposition of two-particle azimuthal correlations measured with the STAR detector in Au + Au collisions for energies ranging from root s(NN) = 7.7 to 200 GeV. The third harmonic nu(2)(3){2} = cos 3(phi(1)-phi(2)), where phi(1)-phi(2) is the angular difference in azimuth, is studied as a function of the pseudorapidity difference between particle pairs Delta eta = eta(1) -eta(2). Nonzero nu(2)(3){2} is directly related to the previously observed large-Delta eta narrow-Delta 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, nu(2)(3){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, nu(2)(3){2} is consistent with zero. When scaled by the pseudorapidity density of charged-particle multiplicity per participating nucleon pair, nu(2)(3){2} for central collisions shows a minimum near root s(NN) = 20 GeV.