Untriggered di-hadron correlations in Pb-Pb collisions at $\sqrt{s_{NN}} =$ 2.76 TeV from ALICE

TL;DR

This paper analyzes untriggered di-hadron correlations in Pb-Pb collisions at 2.76 TeV, revealing structures related to jets, flow, and fluctuations, and examining their dependence on collision centrality and charge.

Contribution

It provides a detailed decomposition of correlation structures, including the soft ridge, and explores the effects of higher harmonic flow components in heavy-ion collisions.

Findings

Nearside Gaussian scales with the number of binary collisions.

Charge dependence observed in the nearside Gaussian.

Inclusion of higher harmonics affects the correlation decomposition.

Abstract

We present measurements of untriggered di-hadron correlations as a function of centrality in Pb-Pb \sNN collisions, for charged hadrons with $p_{T} > 0.15$ GeV$/c$. These measurements provide a map of the bulk correlation structures in heavy-ion collisions. Contributions to these structures may come from jets, initial density fluctuations, elliptic flow, resonances, and/or momentum conservation. We decompose the measured correlation functions via a multi-parameter fit in order to extract the nearside Gaussian, the longer range $\Delta \eta$ correlation often referred to as the soft ridge. The effect of including higher harmonics ($v_{3}$ and $v_{4}$) in this procedure will be discussed. We investigate how the nearside Gaussian scales with the number of binary collisions. Finally, we show the charge dependence of the nearside Gaussian.