The plethora of existenting jet observables in heavy-ion collisions has allowed for an extensive description of jet quenching phenomena over the last decades. Despite this, we still lack a concise theoretical interpretation of the observed data, namely at the level of jet substructure observables. In an attempt to be dominated by perturbative dynamics, one usually relies on grooming methods which remove soft, wide-angle radiation, but even for this scenario, there are still competing explanations for the physical origin of the measured medium-induced modifications. To this end, we present a minimal approach to compute groomed substructure observables, with medium effects treated as an effective energy shift dependent on the jet substructure itself. By matching the NLO dijet matrix element with a leading-logarithmic-accurate parton shower and using an energy-loss model which includes colour coherence effects, we obtain a solid theory-to-data agreement (within 10%) when compared to ALICE and ATLAS data. We also find an overall better agreement with data when including colour coherence effects and we inspect the role of quark–gluon selection bias.
Published by the Jagiellonian University
2026
authors
We present a theoretical framework for jet fragmentation in heavy-ion collisions based on the resummation of large energy logarithms. Exploiting the hierarchy of scales characteristic of jet quenching, we show that the jet function obeys the Banfi-Marchesini-Smye evolution equation, with medium-induced energy loss and color decoherence encoded in the initial condition. This structure reveals a close correspondence with saturation physics. In particular, the coherence angle emerges as the analog of the saturation scale and exhibits the same asymptotic scaling behavior under nonlinear evolution. As a proof of principle, we compute the jet nuclear modification factor to quantify the interplay between vacuum radiation and medium-induced color decoherence. Our framework provides a unified perturbative description of vacuum-like parton showers, medium-induced radiation, and color-coherence effects, paving the way for precision studies of jet quenching at RHIC and the LHC.
P. Caucal, Kevin Eisenberg, Y. Mehtar-Tani· 1 citation
We propose a unified framework for a combined global analysis to constrain leading hadronization effects across the 1-Jettiness class of global event shapes for Deep Inelastic Scattering (DIS). We show that for the subclass of jet-based event shapes where the leading jet direction is determined dynamically event-by-event, the leading hadronization effects can acquire a non-trivial dependence on the hard scattering kinematics. However, this dependence is explicitly calculable, allowing for universality of leading hadronization effects in the 1-Jettiness class. The non-trivial kinematic dependence provides an independent lever arm for simultaneously constraining hadronization effects in the jet-based and DIS thrust event shapes. This universality, combined with the kinematic lever arm, could allow for including the typically ignored peak region, where hadronization effects are most severe, in precision extractions of the strong coupling. We demonstrate the need for such a unified treatment of hadronization effects through comparisons of theoretical predictions with simulation data.
R. Boughezal, Haotian Cao, Z. Kang et al.· 0 citations
The structure of jets produced in high-energy nucleus-nucleus collisions carries information on parton energy loss and interaction in the quark-gluon plasma. This parton energy loss results in migration of jets in terms of transverse momentum, leading to a selection bias in inclusive jet measurements. Using the JEWEL event generator, we investigate a strategy to reduce selection bias and access medium-induced jet broadening, in an experimentally viable way. As a baseline, we first consider large-R $\gamma$+jet events, with little selection bias, which show a clear signal of medium-induced broadening in the jet girth. However, large-R is experimentally inaccessible due to the large underlying event fluctuations in heavy-ion collisions, so we re-cluster a collection of small-radius ($r_{\rm sub}$ = 0.2) jets as a proxy for the large-radius (R = 1.2) jet, which we refer to as a trimmed jet. We quantify to what extent trimmed jets recover signals of jet broadening and investigate its dependence on the subjet cone size and the minimum transverse momentum. We study the internal structure of the subjets to expose the dependence of jet quenching on different subjet configurations, finding a strong narrowing of PbPb jets for the 1-subjet configurations, and a visible signature of medium-induced broadening for sub-leading subjets. The jet radial profile reveals that contributions from medium-induced broadening are distinct from radiation in pp collisions. These contributions are not easily recovered using our trimming procedure, but are substantially enhanced in single-subjet configurations when considering the profile \emph{beyond} the subjet radius. This provides guidance for future experimental studies of jet-medium interactions using $\gamma$+jet in heavy-ion collisions.
Ankita Budhraja, M. Leeuwen, W. Waalewijn· 0 citations
All-heavy pentaquarks provide a unique laboratory for exploring the interplay between exotic-hadron structure, heavy-quark dynamics, and perturbative Quantum Chromodynamics (QCD). In this review, we present the completed release of the uncertainty-aware collinear fragmentation-function family PQ5Q1.1, covering both all-charm (P5c) and all-bottom (P5b) states. The extension to the bottom sector follows the resolution of theoretical and numerical issues affecting heavy-bottom fragmentation and completes the public LHAPDF6 release of the PQ5Q1.1 family. The PQ5Q1.1 functions are constructed within a multimodal framework that accounts for both compact multiquark formation and diquark–antiquark–diquark production mechanisms. A replica-based strategy is adopted to quantify perturbative and nonperturbative uncertainties through missing-higher-order variations (F-MHOUs) and controlled modifications of the hadronic wave-function structure (F-NPWF). For phenomenological applications, we employ the data-validated (sym)JETHAD framework to investigate semi-inclusive pentaquark-plus-jet production at NLL/NLO+ accuracy at the High-Luminosity Large Hadron Collider. We present predictions for differential distributions, assessing the impact of fragmentation dynamics, uncertainty propagation, and hadron-structure effects across the charm and bottom sectors. By combining precision fragmentation tools with collider-oriented observables, this review establishes a unified framework connecting heavy-pentaquark spectroscopy, hadronization mechanisms, and high-energy QCD phenomenology.
We discuss the factorization of scattering processes near partonic threshold at next-to-leading power (NLP) in the threshold variable $1-z$, with $z \equiv q^2/\hat{s}$. We review the general structure of power-suppressed contributions both in Soft-Collinear Effective Theory (SCET) and in a direct QCD approach, and discuss the definition of NLP jet functions as gauge-invariant operator matrix elements in QCD. As a controlled check of the resulting factorization formula, we verify it explicitly at one and two loops for the massive electromagnetic form factor in the limit $m^2 \ll s$, using the method of regions. We conclude by outlining the two challenges that remain for a systematic resummation of NLP logarithms: the treatment of endpoint divergences in SCET convolutions, and the extension of jet functions to radiative processes capable of describing an arbitrary number of soft-gluon emissions -- the latter being the last missing ingredient for exponentiation, given that the purely soft sector is already understood in terms of generalised webs via the replica trick.
Robin van Bijleveld, J. T. Hoeve, E. Laenen et al.· 0 citations
Parton Distribution Functions (PDFs) at large Bjorken-$x$ are mostly constrained by high-energy measurements, and thus risk to absorb the energy-growing effects of unaccounted new physics (NP) if it were present in the high-energy tails of hadron-collider observables used in global PDF fits. If undetected, such contamination biases the resulting PDFs and can potentially hide the absorbed NP signals from subsequent searches. We illustrate this effect in a Standard Model Effective Field Theory (SMEFT) risk-assessment scenario affecting high-mass Drell-Yan production at the High-Luminosity LHC, and compare two strategies to obtain robust PDFs and SMEFT bounds: conservative fits that exclude data above an energy cut, and simultaneous fits of PDFs and Wilson coefficients performed with the {\tt SIMUnet} tool. Both approaches are shown to successfully recover the injected new physics that is otherwise absorbed and hidden by the PDFs.