Parton Propagation and Fragmentation in QCD Matter

TL;DR

The article surveys how high-energy partons propagate and fragment in both cold and hot QCD matter, consolidating experimental results from DIS, DY, h+A, and A+A alongside theoretical frameworks for parton energy loss, medium-modified fragmentation, and prehadron absorption. It contrasts perturbative approaches (GLV/BDMPS, HT, AMY and modified DGLAP) with nonperturbative string- or dipole-based models, highlighting how observables like RM^h, R_AA, p_T-broadening, and dihadron/photon-hadron correlations constrain the space-time picture of hadronisation. The review identifies open issues—such as the heavy-flavour suppression puzzle, production-time scales, and the relative role of prehadrons vs. partons—and proposes multi-differential measurements and next-generation facilities (EIC, RHIC II, LHC) to disentangle competing mechanisms. It emphasizes that a consistent description must bridge cold-nuclear-matter data with hot-QCD-ml environmental effects, enabling tomographic probes of the QGP and refined understanding of confinement dynamics. Overall, the work maps a roadmap for using diverse high-energy processes to extract the dynamics of parton energy loss, hadron formation times, and medium properties across QCD phases.

Abstract

We review recent progress in the study of parton propagation, interaction and fragmentation in both cold and hot strongly interacting matter. Experimental highlights on high-energy hadron production in deep inelastic lepton-nucleus scattering, proton-nucleus and heavy-ion collisions, as well as Drell-Yan processes in hadron-nucleus collisions are presented. The existing theoretical frameworks for describing the in-medium interaction of energetic partons and the space-time evolution of their fragmentation into hadrons are discussed and confronted to experimental data. We conclude with a list of theoretical and experimental open issues, and a brief description of future relevant experiments and facilities.

Figures (64)

• Figure 1: Illustration of universality of PDFs ($\phi_{f/N}$) and FFs ($D_{j \rightarrow h}$) in leading order processes. Clockwise from top left: $e^++e^-$ annihilation, Deep Inelastic Scattering (DIS), lepton pair (Drell-Yan) emission, and hadron production in hadronic collisions. Solid lines indicate leptons, dashed lines quarks. The small black disc represents the perturbatively calculable hard interaction coefficient $\hat{H}_{\rm hard}$.
• Figure 2: Quark propagation inside a target nucleus ("cold QCD matter") in lepton-nucleus ( left) and hadron-nucleus $\rightarrow$ Drell-Yan ( centre) collisions. Right: Hard scattered parton traveling through the "hot QCD matter" produced in a nucleus-nucleus collision.
• Figure 3: LO kinematics for parton production in DIS collisions ( left) and in hadron-hadron collisions ( right). Double lines indicate hadrons or nuclei, thin single lines are partons or leptons. The labels define the particles 4-momenta.
• Figure 4: Kinematic planes for hadron production in semi-inclusive deep-inelastic scattering and definitions of the relevant lepton and hadron variables. The quantities $k$ ($k'$) and $E$ ($E'$) are the 4-momentum and the energy of the incident (scattered) lepton; $p_h$ is the 4-momentum of the produced hadron, and its transverse component relative to the lepton plane is denoted by $\vec{p}_T$.
• Figure 5: Left: RHIC-equivalent phase space of nuclear DIS experiments at $E_e = 27.6$ GeV (HERMES, solid line), at $E_e = 12$ GeV (HERMES and JLab, dashed line), and at $E_e = 280$ GeV (EMC, dot-dashed line). The dotted line shows the borders of the LO pQCD phase space in $p,A+A$ at top RHIC energy, $\sqrt{s_{NN}} = 200$ GeV. The two arrows show the location of the midrapidity region at SPS and FNAL ($p,A+A$) fixed-target experiments. The shaded regions show the region of phase-space experimentally explored at HERMES Airapetian:2007vuvanderNat:2003au and EMC Ashman:1991cx. Right: Hadron-hadron-equivalent EMC and COMPASS ($\ell+A$) phase space at $\sqrt{s_{NN}} = 27.4$ GeV, compared to the SPS and FNAL ($p,A+A$) phase spaces.