The Rise and Fall of the Ridge in Heavy Ion Collisions

TL;DR

This paper explains the evolution of ridge-like correlations in heavy ion collisions as a transformation of initial coordinate-space anisotropies into final momentum-space correlations, providing a predictive framework for different collision energies.

Contribution

It introduces a new interpretation of the ridge phenomenon as initial-state anisotropies converted into momentum correlations and proposes a new scaling variable for analysis.

Findings

The ridge amplitude peaks at intermediate centralities and diminishes in the most central collisions.

A new scaling variable $v_n^2/\epsilon_{n, ext{part}}^{2}$ is proposed for studying length scales.

Predictions are made for the ridge in Pb+Pb collisions at 2.76 TeV.

Abstract

Recent data from heavy ion collisions at RHIC show unexpectedly large near-angle correlations that broaden longitudinally with increasing centrality. The amplitude of this ridge-like correlation rises rapidly, reaches a maximum, and then falls in the most central collisions. In this letter we explain how this behavior can be explained as initial-state coordinate-space anisotropies converted into final-state momentum-space correlations. We propose $v_n^2/\epsilon_{n,\mathrm{part}}^{2}$ as a useful way to study length scales and provide a prediction for the ridge in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV.