Quenching of hadron spectra in media

TL;DR

This work develops a perturbative QCD framework for jet quenching in a dense QCD medium, focusing on how medium-induced gluon radiation reshapes inclusive hadron spectra at large $p_\perp$. The authors express the medium-modified spectrum as a convolution with the energy-loss distribution $D(\epsilon)$ and show that the observable suppression is controlled by a $p_\perp$-dependent shift $S(p_\perp)$ rather than the mean energy loss, linking it to the gluon multiplicity via the quenching factor $Q(p_\perp) = \tilde{D}(n/p_\perp)$. Key ingredients are the transport coefficient $\hat{q}$, governing transverse momentum broadening and radiation with a characteristic scale $\omega_c = \tfrac{\hat{q}}{2} L^2$, which together produce a soft gluon spectrum and a biased energy-loss distribution that dominates quenching in the phenomenologically relevant region. The results reveal a strong infrared sensitivity and show that the effective shift grows as $S(p_\perp) \propto L\sqrt{p_\perp}$ in many regimes, underscoring that interpreting jet quenching requires the full energy-loss distribution rather than just the mean energy loss. Limitations include the static-medium assumption and the Bethe–Heitler regime, pointing to future work with dynamical media to extract medium properties from data.

Abstract

We determine how the yield of large transverse momentum hadrons is modified due to induced gluon radiation off a hard parton traversing a QCD medium. The quenching factor is formally a collinear- and infrared-safe quantity and can be treated perturbatively. In spite of that, in the $p_\perp$ region of practical interest, its value turns out to be extremely sensitive to large distances and can be used to unravel the properties of dense quark-gluon final states produced in heavy ion collisions. We also find that the standard modelling of quenching by shifting $p_\perp$ in the hard parton cross section by the mean energy loss is inadequate.