A theoretical study of heavy-ion jets reports a saturation-like pattern in the way its calculated coherence angle evolves. The angle is the model’s scale for tracking angular coherence within a jet; in the calculation, it moves toward smaller values as the evolution proceeds. The same framework is used for illustrative comparisons of the nuclear modification factor, RAA — the medium result divided by a vacuum result — rather than measurements from a collider.
The work is a model study, built from analytic formulae and numerical solutions for jet fragmentation, inclusive jet production and energy carried outside the jet in a modeled heavy-ion or quark–gluon-plasma environment. It uses no empirical dataset or participant sample. Its percentages are outputs of calculation scenarios rather than measurements from observed collisions.
A single evolution for several jet effects
Researchers ask whether one all-order collinear-soft evolution can describe out-of-jet energy transport together with vacuum radiation and medium-induced color decoherence in heavy-ion jets. Color decoherence here means the loss of a shared quantum connection between parts of a radiating jet, and the calculation treats it as part of the starting condition.
That evolution uses the Banfi–Marchesini–Smye equation, usually shortened to BMS. The calculation takes the large-Nc limit and a small-cone limit in which the jet radius R is much smaller than 1.
At the stated logarithmic accuracy, medium-induced and vacuum energy loss factorize in Laplace space. The medium energy-loss distribution serves as the initial condition for the BMS evolution.
For the proof-of-concept nuclear-modification calculation, the medium-initial-condition result is divided by the vacuum result. The setup uses an evolution parameter τ of 0.2, a coupling parameter of 0.12 and N equal to 5.
A moving front and a late-evolution formula
As τ increases, the calculated energy-loss distribution develops a traveling-wave front that moves toward smaller angles. That front’s shape follows geometric scaling: the relevant angular dependence is organized by θ12/θc(τ), the angle between two directions divided by the evolving coherence angle.
The study treats θc as the jet-quenching counterpart of a saturation scale — an evolving reference angle in the calculation. At large evolution, it gives the asymptotic form ln(θc(τ)) = -cτ + b ln(τ) + constant + O(τ^-1/2), with c approximately 2.44 and b approximately 1.20.
The numerical solution and analytic asymptote agree very well for τ around 5 or greater. At the phenomenological range τ around 0.2–0.5, the vacuum dynamics has not reached its universal regime and the spectrum remains sensitive to the initial condition.
The modelled differences depend on the scenario
For an LHC-like case with τ around 0.2, the reported smooth-transition power corrections are on the order of 20%. The comparison also reports a BMS effect on RAA of about 10%.
Across the LHC-like to RHIC-like cases, the calculation predicts a relative variation in θc of about 10% to 25% for τ around 0.2–0.5 under BMS evolution. In a separate RHIC-like example, with τ around 0.4, transverse momentum pT around 20 GeV and N around 8–10, the authors report model modifications on the order of 40% and 25%. They also say RAA remains sensitive to the initial medium condition.
These figures are outputs of the stated model scenarios, not measurements from RHIC or the LHC, and the study reports no agreement with data from either collider. At τ around 0.2–0.5, the calculation also remains sensitive to the selected initial condition.
What the first demonstration leaves open
The authors describe the framework as a first demonstration and say higher phenomenological accuracy requires systematic extensions, including solving the BMS evolution beyond the small-cone approximation.
The illustrative calculation neglects geometric effects and assumes that all radiated energy is lost outside the jet. At τ around 0.2–0.5, the universal asymptotic regime has not been reached, and the supplied analysis reports no statistical uncertainty intervals or uncertainty propagation.
The document is an arXiv preprint, version 1, dated 26 August 2026; no journal or peer-review status is reported in the supplied metadata.
Paper data and sources
Original title: Jet Quenching Meets Gluon Saturation
Authors: Paul Caucal, Kevin Eisenberg, Yacine Mehtar-Tani
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-26
DOI: Not available
Original paper · Full text