Medium modification of jet fragmentation in Au+Au collisions at sqrt(s_NN)=200 GeV measured in direct photon-hadron correlations

TL;DR

This study measures how jet fragmentation in heavy-ion collisions differs from proton-proton collisions at 200 GeV, revealing suppression at high momentum fractions and enhancement at low fractions, indicating medium-induced modifications.

Contribution

It provides the first detailed measurement of medium modification of jet fragmentation functions using direct photon-hadron correlations at RHIC energies.

Findings

Suppression of high z_T jet fragments in Au+Au collisions.

Enhancement of low z_T fragments at large angles.

Evidence of energy redistribution within the medium.

Abstract

The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the photon is an excellent approximation to the initial p_T of the jet and the ratio z_T=p_T^h/p_T^\gamma is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. I_ AA, the ratio of jet fragment yield in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high z_T. The fragment yield at low z_T is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles.