Modification of jet-like correlations in Pb-Au at the SPS

TL;DR

This study analyzes high-$p_t$ two-particle azimuthal correlations in Pb-Au collisions at SPS energies, revealing a broad away-side correlation with a dip, excess soft particles, and indications of medium energy transfer.

Contribution

It provides the first high-statistics measurement of jet-like correlations at SPS energies, showing similarities to RHIC results and evidence of medium interactions.

Findings

Broad away-side correlation with dip at $ riangle\phi \\approx \\pi$

Excess of soft particles compared to PYTHIA predictions

Charge correlations suggest energy transfer to medium

Abstract

A high statistics study of high-$p_t$ two-particle azimuthal correlations in Pb-Au at $\sqrt{s_{\rm NN}}=17.2$ GeV, performed by the CERES experiment at the CERN-SPS, is presented. A broad away-side correlation with significant dip at $\Delta\phi\approx\pi$ is observed. The shape and magnitude of the correlation is similar to measurements at RHIC. In comparison to PYTHIA calculations, we observe a significant excess of soft particles at the away-side. A study of charge correlations between trigger and associated particles disfavors vacuum fragmentation of the away-side jet and suggests significant energy transfer of the hard-scattered parton to the medium.