Color transparency and suppression of high-pT hadrons in nuclear collisions

TL;DR

This paper explains the suppression of high-p_T hadrons in nuclear collisions through color transparency effects, showing good agreement with LHC data and estimating medium properties without adjustable parameters.

Contribution

It introduces a model linking short production length and color transparency to nuclear suppression, aligning with recent experimental data and providing parameter estimates.

Findings

Nuclear suppression mainly due to survival probability of colorless dipoles.

Steep rise of R_{AA}(p_T) with p_T at LHC energies.

Transport coefficient .8 GeV^2/fm consistent with J/Psi suppression analysis.

Abstract

The production length l_p of a leading (large z_h) hadron produced in hadronization of a highly virtual high-p_T parton is short because of the very intensive vacuum gluon radiation and dissipation of energy at the early stage of process. Therefore, the main part of nuclear suppression of high-p_T hadrons produced in heavy ion collisions is related to the survival probability of a colorless dipole propagating through a dense medium. This is subject to color transparency, which leads to a steep rise with p_T of the nuclear ratio R_{AA}(p_T), in good agreement with the recent data from the ALICE experiment at LHC, CERN. No adjustment, except the medium density is made, and the transport coefficient is found to be \hat q_0=0.8 GeV^2/fm. This is close to the value extracted from the analysis of RHIC data for J/Psi suppression, but is an order of magnitude smaller than the value found from jet quenching data within the energy loss scenario. Although the present calculations have a status of a postdiction, the mechanism and all formulas have been published, and are applied here with no modification, except the kinematics. At the same time, p_T-dependence of R_{AA} at the energy of RHIC is rather flat due to the suppression factor steeply falling with rising x_T, related to the energy conservation constraints. This factor is irrelevant to the LHC data, since x_T is much smaller.