$\Delta\eta$-$\Delta\phi$ correlations and the ridge structure in STAR

Abstract

Triggered di-hadron correlation studies using central Au+Au collisions at $\sqrt{S_{NN}}$ = 200 GeV in STAR revealed a novel ridge-like structure in two dimensions ($\Delta\eta$,$\Delta\phi$) for high $p_{T}$ particles. A similar structure is also present in an inclusive un-triggered di-hadron correlation analysis. We study the <$p_{T}$> evolution of di-hadron correlations by increasing the lower $p_{T}$ acceptance of both charged particles. A smooth evolution of data is observed and our results reproduce the triggered analysis structure near <p_{T}> = 2.7 GeV/c. We quantify the correlation structure evolution by fitting a model function. The model function emphasizes possible initial state fluctuation contributions via the use of higher harmonic model components $v_{n}$ (n=1,2,3,4,5) and a remainder which is modeled via an asymmetric 2d Gaussian. The extracted parameters are compared to model predictions and p+p data at $\sqrt{S_{NN}}$ = 200 GeV and possible origins of the nearside structure are discussed.