Welcome to Subatech

• Pol-Bernard Gossiaux

Room: Amphi G.Besse

2026 GdR QCD AG

• Gines MARTINEZ (Subatech CNRS/IN2P3 - IMT Atlantique - Nantes Universite)
• Savvas Zafeiropoulos (CPT Marseille, CNRS)
• Raphaël DUPRE
• Audrey Francisco (CEA)

Room: Amphi G.Besse

The proton charge radius puzzle: observation, bias and scientific rigor.

• Adam HOBALLAH (IJCLab CNRS-IN2P3)

Room: Amphi G.Besse The repeated measurements of the proton charge radius have led to more precise estimations of this essential quantity in physics. However, driven by the same attempt to improve the precision of the measurements of the radius, researchers unintentionally tend to validate previous findings leading in some cases to inconsistencies. The proton radius puzzle constitutes a clear example of how observational bias can alter physics measurements. This talk will give a brief history of the proton charge radius measurements and will focus on recent measurements showing how these extractions were strongly biased by the ones obtained by previous experiments. I will discuss how equally valid assumptions on the extraction of the radius can strongly influence the obtained results arguing that these assumptions are to be considered as sources of systematic errors. I will then discuss recent developments from experimental side and expected new measurements and will eventually discuss our contribution on the phenomenological side that we did at IJCLab in Orsay.

Reconstructing generalized parton distributions with neural fields: what the data leave free

• Marija Cuic (Irfu, CEA, Université Paris-Saclay/Aidas)

Room: Amphi G.Besse Generalized parton distributions (GPDs) encode the three-dimensional partonic structure of the nucleon, but exclusive processes such as deeply virtual Compton scattering constrain them only in part of their kinematic domain — the so-called DGLAP region — while leaving the complementary ERBL region essentially undetermined by data. A standard way to relate the two is through the double distribution: a single underlying function whose Radon transform generates the GPD, tying the measured and unmeasured regions together through Lorentz covariance. We represent this double distribution as a neural field — a coordinate network encoding it continuously — and enforce the physical support, symmetry, and polynomiality by construction. Trained on Compton form factor pseudodata with realistic experimental coverage, this approach reproduces the input GPD across both regions, while a direct parametrization of the GPD fails in the unmeasured region — quantifying the information carried from measured to unmeasured kinematics by the double-distribution structure. We then ask how much of the reconstruction is fixed by data and how much by the modelling assumptions. Using a Jacobian analysis, we identify the directions in model space that deform the GPD while leaving every predicted observable unchanged — deformations the data are blind to by construction — and calibrate their size to the tolerance of the data. The same framework quantifies how much future measurements, in particular at the Electron-Ion Collider, would shrink this residual freedom, providing a data-driven, assumption-aware uncertainty for GPD extractions.

Deeply Virtual Compton Scattering off 4He with the ALERT experiment and CLAS12 spectrometer at Jefferson Lab

• Félix TOUCHTE CODJO (PHE/JLab-EIC)

Room: Amphi G.Besse The goal of the ALERT experiment is to advance the understanding of the QCD structure of the nuclear matter. It proposes a precise measurement of the electro production of a real photon through the interaction with $^4\mbox{He}$ and $^2\mbox{D}$ targets. This process, referred to as Deeply Virtual Compton Scattering (DVCS), gives access to Generalized Parton Distributions (GPDs). The GPDs are used to perform a tomography of the quarks inside the nucleus, to understand the origin of its spin, and to access the shear forces inside it. To achieve this experiment, the Continuous Electron Beam Accelerator Facilities of Jefferson Lab, which can deliver spin polarized electron beam up to 11 GeV, are used. All the final states of the process are detected by pairing the CLAS12 spectrometer with the novel low-energy ALERT recoil tracker. ALERT consists of a hyperbolic drift chamber for track reconstruction and an array of scintillators for particle identification. It is specifically designed to detect low-energy recoil fragments ($^4\mbox{He}$, $^3\mbox{He}$, $^3\mbox{H}$, $^2\mbox{H}$, p). After the success of the data taking, from April to September 2025, efforts are currently dedicated to the finalization of the reconstruction software and the calibration of the data. In this talk, I will briefly describe the main goal of the ALERT experiment, detail the latest update of the data reconstruction chain, and present a preliminary extraction of the Beam Spin Asymmetry of the coherent DVCS off $^4\mbox{He}$.

Gluon production in the Color Glass Condensate from BCFW recursion

• Francois Gelis (IPhT)

Room: Amphi G.Besse In the Color Glass Condensate framework, the colliding projectiles are described as classical color currents. Gluon production at leading order in the coupling is obtained from the retarded solution of the classical Yang-Mills equations, with these currents acting as sources. However, while the final gluon spectrum is gauge invariant, the classical color field from which it is obtained is gauge dependent. This makes the intermediate steps of this approach unnecessarily complicated, as some effort is spent to also determine the gauge dependent part of the field, which is then discarded when one calculates a gauge invariant observable. In this work, we use a generalization of BCFW recursion applicable to off-shell gluons in order to calculate directly the gauge independent gluon production amplitude. This approach allows all manipulations to be performed in terms of gauge invariant amplitudes instead of gauge dependent Feynman diagrams, and therefore provides a gauge agnostic way to obtain the result.

Probing nPDF at the LHC using electromagnetic processes and quarkonia

• Djessy BOURGEAIS (Subatech UMR6457)

Room: Amphi G.Besse Extracting parton distribution function is crucial for understanding the physic of colliders, since it represent the probability distribution of partons inside a hadron. Recent PDF collaborations as NNPDF, EPPS or CTEQ have used recent LHC data on quarkonia and/or charmed mesons to improve the uncertainty of nPDF at small values of $x$. However, those particles are actually sensitive to another nuclear effect, namely fully coherent energy loss (FCEL), which needs to be incorporated for a reliable extraction of parton densities. In this study, $J/\psi$ production is computed in the color evaporation model (CEM) taking into account both nPDF and FCEL effects. Using reweighting techniques, new nPDFs are extracted from LHC data. The comparison between nPDF sets obtained with and without FCEL shows inconsistencies, which illustrates the need to take into account FCEL effect for a proper nPDF extraction.

Overview of precision QCD calculations

• Hua-Sheng Shao (CERN)

Room: Amphi G.Besse In this talk, I will provide an overview of some recent results in precision QCD calculations, with particular emphasis on fixed-order results.

Bridging information from lattice and phenomenology on the Collins-Soper kernel

• Matteo Cerutti (CEA Paris-Saclay)

Room: Amphi G.Besse In this talk, I will present the first joint extraction of the Collins–Soper kernel (CSK) combining experimental and lattice QCD data within a transverse-momentum-dependent (TMD) analysis. The CSK governs the evolution of TMD distributions and is a key ingredient in their phenomenological extraction. We investigate the impact of lattice information through both Bayesian reweighting of an existing TMD fit based on a neural-network parametrisation and a joint fit to experimental and lattice data. In both cases, we consistently obtain a non-negligible modification of the central value and a significant reduction of the uncertainty band. This opens the way for more precise TMD extractions exploiting the complementary information provided by experimental measurements and lattice calculations.

Quarkonium and HF, Quo Vadis

• Pol-Bernard Gossiaux

Room: Amphi G.Besse Une petite revue sympathique, sans prétention et très biaisée de certains développements théoriques récents..

Vector meson photoproduction as a probe of nuclear structure at the LHC

• Olga Bessidskaia Bylund

Room: Amphi G.Besse In ultra-pheripheral photo-nuclear interactions, the colliding ions are separated by more than the sum of their radii and the reaction proceeds via photon emission from one nucleus followed by interaction with the target nucleus. A vector meson can be produced if the photon interacts with gluons in the target. Such processes are sensitive to the nuclear structure, including modifications to the nuclear parton distribution functions and the geometrical shape of the nuclei. Coherent and incoherent VM photo-production (where either the whole nucleus or a single nucleon acts as a target) in high-energy collisions allow us to probe the nuclear structure at low values of Bjorken-x, where saturation and shadowing effects are expected to become important. On the other hand, VM photo-production in fixed target mode with SMOG2 at LHCb, provides access to higher Bjorken-x at different kinematics. We perform a phenomenological study with the STARLIGHT Monte Carlo generator, assessing the expected experimental precision at LHCb and ALICE on the cross sections of coherent and incoherent VM photo-production in light ion Run 3 data. The discriminating power between these contributions is investigated, in order to learn whether such measurements will be able to differentiate between various models for nuclear structure. Additionally, I discuss possible extensions of VM photo-production measurements to new species of colliding ions at the LHC Run 4 and implications for theoretical nuclear physics.

Upsilon hadroproduction and vector meson photoproduction with SMOG2 at LHCb

• Federica FABIANO (IJCLab (CNRS/IN2P3, Univ. Paris-Saclay))

Room: Amphi G.Besse **Abstract**: The SMOG2 fixed-target system at LHCb provides a unique opportunity to study cold nuclear matter effects and nuclear structure in a complementary kinematic region with respect to collider measurements. This contribution presents the first measurement of the production of the $\Upsilon(nS, n=1,2,3)$ states in fixed-target collisions where the three states are separately reconstructed. The $\Upsilon(1S)$ production cross-section per nucleon and the excited-to-ground state production ratios ($\Upsilon(nS, n=2,3)/\Upsilon(1S)$) are measured in pAr and pp collisions at $\sqrt{s_{NN}}=113$ GeV using 2024 SMOG2 data. The analysis of both samples also permits the measurement of the $\Upsilon$ nuclear modification factor $R_{pA}$. The contribution also presents studies on the exclusive $\rho$ and $J/\psi$ photoproduction in PbAr fixed-target collisions at $\sqrt{s_{NN}}=70.9$ GeV. The measurement of the $\rho$ photoproduction cross-section as a function of the momentum transfer $|t|$ or as a function of the centre-of-mass rapidity $y^*$ provides a way to disentangle different nuclear shape models and to test ab-initio calculations of the nuclear structure.

Probing the Standard Model to eleven digits with the muon magnetic moment

• Laurent Lellouch (CNRS & Aix-Marseille U.)

Room: Amphi G.Besse The Muon g−2 Experiment at Fermi National Accelerator Laboratory recently published the results of its six-year data-taking campaign, reporting a measurement of the muon's anomalous magnetic moment with unprecedented precision of 0.127 parts per billion, providing one of the most stringent tests of the Standard Model. However, to fully leverage this experimental tour de force in the search for new fundamental physics, a theoretical prediction of comparable accuracy is required. In this talk, I will survey the current experimental and theoretical landscape of the muon's anomalous magnetic moment before presenting first-principles calculations of the leading hadronic contributions, the largest source of uncertainty in the Standard Model prediction. When combined with all other Standard Model contributions, this calculation yields a prediction that agrees with experiment within half a standard deviation, confirming the Standard Model to eleven significant digits and sharpening constraints on physics beyond it.

Muon g-2: an overview of hadronic contributions

• Anton Rebhan (Vienna University of Technology (TU Wien))

Room: Amphi G.Besse The latest Standard Model prediction of the muon anomalous magnetic moment is now consistent with the experimental value, but it has an uncertainty that is more than four times larger than the experimental error. To fully exploit the experimental result as a constraint on or indicator for BSM physics, the Standard Model prediction needs to be further improved. The theoretical uncertainty is entirely due to hadronic contributions, namely from hadronic vacuum polarization (HVP) and from hadronic light-by-light (HLbL) scattering. In the case of HVP, the earlier Standard Model prediction from 2020, which was dominated by the data-driven dispersive approach, had to be abandoned due to growing discrepancies in the experimental input, whereas lattice QCD has now reached almost the previously assumed accuracy while shifting the result significantly. On the other hand, the smaller but less precisely known HLbL contribution has been improved with only a small tension between lattice QCD and the dispersive approach. In the latter, the previous uncertainty from poorly determined axial-vector meson contributions and related short-distance contributions could be significantly reduced, in remarkably quantitative agreement with holographic QCD calculations. The largest HLbL uncertainty is now due to tensor-meson contributions, where dispersive and holographic results however strongly disagree. The latter would remove the tension with current HLbL lattice results, while the former enhance it. Upcoming results from experiments such as BESIII hold the promise to resolve this issue and could further sharpen the precision of the HLbL contribution.

Next-to-leading Order QCD Factorization for Energy Flow in Electron-Ion Collisions at Twist 4

• Omar Elgedawy (Ecole Polytechnique, CPHT)

Room: Amphi G.Besse Energy-energy correlators (EECs) have recently emerged as powerful, rigorously established infrared- and collinear-safe (IRC-safe) observables for probing QCD dynamics in the vacuum. However, their IRC safety and factorization properties in the presence of a nuclear medium remain unexplored. In this talk, I will present the first derivation of QCD factorization at next-to-leading order (NLO) for an energy-flow observable in a physical scattering process involving a nuclear medium. Working within the high-twist framework, we calculate the twist-4 contributions to the angular width of the one-point energy correlator (OPEC) in semi-inclusive deep inelastic electron-ion scattering, explicitly demonstrating the IRC safety of medium-enhanced contributions. We show that the OPEC angular spreading width provides a highly sensitive, hadronization-free probe of transverse momentum broadening in cold nuclear matter. This NLO factorization framework establishes a theoretical foundation for extending energy correlators to a broad class of high-energy processes in nuclear environments and opens the possibility of global analyses of nuclear properties using OPEC observables.

Measurement of the $b$-jet production cross section in proton-proton collisions at $\sqrt{s} = 13.6$ TeV

• CLEMENT LOTTEAU

Room: Amphi G.Besse Measuring $b$-jet production in proton--proton (pp) collisions is important to test perturbative Quantum Chromodynamics (pQCD) calculations and form a baseline for heavy-ion collision systems. In this contribution, the measurement of $b$-jet production cross section in pp collisions at $\sqrt{s}=13.6$ TeV with ALICE is presented. Charged jets are reconstructed at mid-rapidity ($|\eta_{\mathrm{jet}}|<0.5$) using the anti-$k_{\mathrm{T}}$ algorithm with $R$=0.4 in the transverse momentum interval $5 < p_{\mathrm{T}}$ (GeV/$c$) $< 140$. The $b$-jets are tagged with Boosted Decision Trees (BDTs) which is a machine learning based classification method. In order to extract the $b$-jet fractions from data, a 2D template fit method is introduced. The measurement is compared to POWHEG + PYTHIA8 model calculations as well as to Run-2 results in pp collisions at $\sqrt{s} = 13$ TeV. Finally an initial look on $b$-jet production cross-section measurement in Oxygen--Oxygen collisions is presented, paving the way for jet quenching studies in light and heavy-ion systems.

Spatially inhomogeneous confinement-deconfinement phase in rotating quark-gluon plasma

• Maxim Chernodub (Institut Denis Poisson, Tours)

Room: Amphi G.Besse Using first-principles numerical simulations, we find a new spatially inhomogeneous phase in a rotating (quark-)gluon plasma in thermal equilibrium. This mixed phase simultaneously contains regions of both confining and deconfining states in thermal equilibrium, separated by a spatial transition. We calculate the critical temperature of the local transition as a function of angular velocity and radius for a full (imaginary) rotating system. An analytic continuation of the results to the domain of real angular frequencies indicates that the confinement phase localizes at the periphery of the rotating system, while the deconfinement phase appears closer to the rotation axis, thus disobeying the naive picture based on a straightforward implementation of the Tolman-Ehrenfest law. Our simulations also reveal unusual mechanical properties of pure gluon plasma.

SUBA-Jet 1.2: Incorporating Coherence Effects in Jet Evolution through a Quark–Gluon Plasma

• Fabrizio Murgana (Subatech, Nantes)

Room: Amphi G.Besse We present SUBA-Jet 1.2, a new version of the SUBA-Jet Monte Carlo framework that incorporates medium-induced coherence effects in the evolution and energy loss of jets propagating through a quark-gluon plasma (QGP). The model combines a vacuum-like parton shower with medium-induced interactions described through a BDMPS-inspired approach. Coherence is implemented through angular ordering constraints together with two effective prescriptions: one based on the decoherence probability of the dominant emitter and another based on the transverse separation of emitters relative to the resolving power of the medium. Both approaches reduce the effective number of BDMPS radiators resolved by the medium. This development represents a first step towards SUBA-Jet 2.0, where coherence effects will be incorporated into a fully emitter-based description of jet evolution.

Heavy-flavour jet measurements with ALICE

• Yoshini BAILUNG (Institut de Physique des 2 Infinis (IP2I) de Lyon, CNRS-IN2P3, Université de Lyon)

Room: Amphi G.Besse Measurements of heavy-flavour jets in pp collisions provide important tests of Quantum Chromodynamics (QCD) calculations. Jet substructure observables offer insight into the parton-shower evolution and the different radiation patterns of quarks and gluons arising from the different Casimir colour factors and parton masses. Comparisons between jets containing heavy-flavour baryons or heavy-flavour mesons probe heavy-quark hadronisation mechanisms and test the assumption of universality of charm-quark hadronisation across different collision systems. In this contribution, a collection of recent ALICE measurements about heavy-flavour jets in pp collisions is presented. First, a set of observables involving charm jets identified by reconstructing $\mathrm{D^{0}}$ mesons is shown. We discuss measurements related to different choices of jet-axis definition, complemented by the generalised jet-angularity measurements for $\mathrm{D^{0}}$-tagged jets. These two measurements provide systematic insight into the radiation pattern and fragmentation of charm quarks during the parton-shower evolution. Then, we present the first measurement of the energy-energy correlator in $\mathrm{D^{0}}$-tagged jets, which resolves the angular structure of the energy flow of QCD radiation and allows for the separation of perturbative and non-perturbative regimes. Extending these studies in the charm-baryon sector, we compare the results of $\mathrm{D}$-meson jets with those of $\mathrm{\Lambda^{+}_{c}}$-tagged jets, thereby providing insight into charm-quark hadronisation mechanisms. Finally, we present the new b-jet production cross section measured with a b-jet tagging algorithm based on a graph neural network. These results provide new benchmarks for perturbative QCD calculations and establish a baseline for future b-quark energy loss studies in heavy-ion collisions.

Heavy-ion data match finite-temperature lattice QCD

• Jean-Yves OLLITRAULT (IPhT Saclay)

Room: Amphi G.Besse A precise value of the speed of sound of QCD at a temperature T=220 MeV can be extracted from 2024 ATLAS data in ultracentral Pb+Pb collisions. One observes an increase of the mean transverse momentum with the charged multiplicity for the 0.4% most central collisions. This increase stems from an increase in the temperature, from which one can extract the speed of sound after careful corrections. The resulting value, cs/c=0.496±0.008, is in perfect agreement with predictions from lattice QCD at finite temperature. https://arxiv.org/abs/2603.09647 Phys.Lett.B 880 (2026) 14073

Data driven approach to jet tomography

• Yacine Mehtar-Tani (BNL)

Room: Amphi G.Besse Jet tomography aims to reconstruct the properties of the quark-gluon plasma from the modification of energetic particles and jets traversing it. Because jets contain many intertwined length and time scales, no single observable provides a complete image of their interaction with the medium. I will discuss a multi-messenger approach to jet tomography in which inclusive jet suppression, $R_{AA}$, and energy-energy correlators provide complementary views of the same underlying dynamics. While $R_{AA}$ characterizes the overall strength of jet quenching, energy-energy correlators reveal how that modification is distributed across the angular structure of the jet. Together, these observables can distinguish whether the plasma interacts coherently with a jet as a single color charge or resolves the individual partons produced during its fragmentation. Measurements by the experimental programs at RHIC and the LHC probe this physics over complementary collision energies and jet kinematics, opening a path toward determining not only how strongly the quark-gluon plasma quenches jets, but also the spatial and temporal resolution with which it probes them.

Toponium at the LHC: a new frontier in top-quark physics

• Benjamin Fuks (LPTHE Paris / Sorbonne Université)

Room: Amphi Kastler The top quark, the heaviest known elementary particle, has long been thought unable to form bound states. However, intriguing hints in recent LHC data suggest that toponium, a short-lived quasi-bound state of a top-antitop pair, might have left observable traces in data and perhaps even been observed for the first time. In this talk, I will discuss why toponium provides a unique laboratory for studying the strong interaction in the non-relativistic regime, how modern techniques allow us to incorporate bound-state effects into state-of-the-art collider simulations, and which experimental signatures could reveal the presence of toponium in present and future LHC data. Finally, I will highlight recent results, ongoing searches and the exciting prospects for using toponium as a new window into top-quark physics.

Measurements of top-quark pair production at the threshold at the LHC

• Emilien Chapon (CEA / Irfu / DPhP)

Room: Amphi Kastler Recent data from the Large Hadron Collider has enabled groundbreaking measurements of top quark properties, particularly those sensitive to the tt̄ (top-antitop) threshold region. This includes exploring phenomena like the contributions of quasi-bound states ("toponium"), which were once inaccessible. This talk will review the latest advancements in this field from the ATLAS and CMS collaborations.

AI/ML Assisted Tracking for the Central Detector of the CLAS12 Experiment

• Mathieu Ronayette (CEA Saclay)

Room: Amphi Kastler The CLAS12 experiment is a fixed-target experiment located at the Thomas Jefferson Laboratory in Newport News, USA and dedicated to the study of hadronic physics, in particular the structure of the nucleon and hadron spectroscopy. The Central Detector (CD) of CLAS12 provides tracking capabilities for charged-particle at large polar angles. However background hits from electronic noise or neutral particles can contaminate the clusters, distort reconstructed tracks, and lead to fake tracks. To mitigate these effects, we investigate a machine-learning approach to identify signal hits and suppress background prior to track reconstruction. As a proof of principle, simulated events containing a single muon were used to train Graph Neural Networks (GNNs), which are particularly well suited to the irregular geometry and hit-based representation of particle detectors. Two architectures, GravNet and GarNet, have been investigated, and their performance was studied as a function of the input features and model hyperparameters. Ongoing work focuses on validating the approach with multiple-particle events and under realistic reconstruction conditions. The impact of ML-based denoising on the performance of charged-particle tracking and its applicability to physics analyses using CLAS12 data will be shown in this talk.

Deep-Learning for charged particle tracking

• Corentin Allaire (IJCLab, Université Paris-Saclay, CNRS/IN2P3)

Room: AMphi Kastler he reconstruction of particle trajectories is a key challenge of many high-energy and nuclear physics experiments. Indeed, its performance directly impacts particle identification and physics performances while also representing one of the primary CPU consumers of many experiments. As the luminosity of particle colliders increases, this reconstruction will become more challenging and resource-intensive. New algorithms are thus needed to address these challenges efficiently. Since the TrackML challenge in 2018, the use of Deep Learning has emerged as a viable alternative to traditional tracking techniques, thanks to its ability to exploit global event context and its potential for fast inference on GPU systems. This period also saw the development of ACTS, the Open-Source tracking library that became a central testing environment for many new DL algorithms. In this talk, after a short overview of the traditional tracking techniques and the ACTS library. We will present an overview of what has been developed so far in the DL world, including Simple Neural Network, Graph Neural Network and Transformers. And we will discuss the advantages and disadvantages compared to the classical solution.

High-energy nuclear collisions: a new laboratory for many-body nuclear dynamics

• Giuliano Giacalone

Room: Amphi Kastler Relativistic nuclear collisions have emerged as a new laboratory for studying many-body correlations among nucleons in nuclear ground states. Focusing on ultra-central collisions, where nearly all nucleons participate, I will discuss how long-range nuclear correlations leave distinct imprints in final-state multi-particle correlation observables, and how scale separations inherent to the QCD description of these processes help establish this connection. I will review the experimental evidence of nuclear correlation effects across systems ranging from 20Ne collisions at the LHC to 238U collisions at RHIC, and their interpretation through traditional geometric descriptions of nuclear shapes and clustering. I will emphasize progress in disentangling nuclear-structure from collision-dynamics effects within the pipeline of global Bayesian analyses of LHC data. I will conclude by outlining the physics opportunities offered by collisions of new ion species in future LHC runs, addressing questions at the intersection of high- and low-energy nuclear physics.

Hadron 2030

• BARBARA ERAZMUS (IN2P3/CNRS)

Room: Amphi Kastler

Table Ronde : Prospectives GdR QCD

• Audrey Francisco (CEA)
• Herve Moutarde (CEA-IRFU-SPHN)
• Marcella Grasso (IN2P3)
• Matteo Cacciari (LPTHE)
• Raphaël DUPRE
• Savvas Zafeiropoulos (CPT Marseille, CNRS)
• Stefano Matthias Panebianco (French Ministry of Research and Innovation)
• Gines MARTINEZ (Subatech CNRS/IN2P3 - IMT Atlantique - Nantes Universite)

Room: Amphi Kastler

QCD physics at FCC-ee

• Matteo Marcoli (CERN)

Room: Amphi Kastler The electron-positron stage of the Future Circular Collider (FCC-ee) is aiming at direct and indirect searches for physics beyond the SM in a new 91-km tunnel at CERN. In addition, the FCC-ee offers unique possibilities for high-precision studies of the strong interaction in the clean environment provided by ee collisions, thanks to its broad span of center-of-mass energies, ranging from the Z pole to the top-pair threshold, and its huge integrated luminosities yielding and jets from Z and W bosons decays respectively, pure gluon jets from Higgs boson decays, as well as $O(2\times10^6)$ top quarks. In this contribution, we will summarize the impact that the FCC-ee will have on our improved knowledge of the strong force including: (i) QCD coupling determinations with permil uncertainties, (ii) ultraprecise studies of parton radiation and jet properties (ligh-quark/heavy-quark/gluon discrimination, jet substructure, etc.); and (iii) accurate scrutiny of nonperturbative QCD phenomena (color reconnection, hadronization, final-state hadron interactions,...).

Charmonium production in Pb–-Pb collisions at forward rapidity with ALICE

• Sara GARETTI (IJCLab, Université Paris-Saclay)

Room: Amphi Kastler Quarkonium production in high-energy heavy-ion collisions is a key tool to study the production and the properties of the quark-gluon plasma (QGP), a state of matter in which quarks and gluons are no longer confined inside hadrons. Charmonia are quarkonium bound states consisting of a charm and an anti-charm quark. Charmonium production in Pb--Pb collisions is sensitive to the quark–gluon plasma through color-screening–induced suppression and regeneration from uncorrelated $\mathrm{c}\bar{\mathrm{c}}$ pairs, whose interplay depends on the medium properties and on the quarkonium binding energy. A comparative study of J/$\psi$ and $\psi$(2S) production provides a powerful probe of these effects: the more weakly bound $\psi$(2S) is expected to be more strongly suppressed, while regeneration is predicted to play a significant role at LHC energies, making the relative production of the two states especially sensitive to the medium evolution and challenging for theoretical models. In this talk, I will present the analysis status of inclusive J/$\psi$ and $\psi$(2S) production at forward rapidity (2.5 $< y <$ 4) in Pb–-Pb and OO collisions at a center-of-mass energy per nucleon pair of \sqrts. The analysis in Pb--Pb is based on the data collected in 2023 by the upgraded ALICE detector during LHC Run 3, which provide a larger data sample compared to previous data-taking periods. The results will be compared to similar measurements from data collected during LHC Run 2, and with theoretical models.

Renormalon subtracted nonrelativistic QCD for heavy hadron systems

• Simon VAIVA (CPT Marseille)

Room: Amphi Kastler Precision perturbative spectroscopy of heavy hadrons is limited by the leading infrared renormalon of the static potential, which drives factorial growth in the perturbative series and leaves a large residual dependence on the renormalization scale. We present a renormalon-subtracted formulation of potential nonrelativistic QCD, combining variational and Green's-function Monte Carlo methods with NNLO static two- and three-body potentials. Minimal renormalon subtraction (MRS) systematically resums the leading factorially growing terms, stabilising perturbative convergence and markedly reducing scale dependence. 
Tuning the charm and bottom quark masses to the spin-averaged 1S quarkonium states, we predict the masses of the triply-heavy baryons $\Omega_{ccc}$, $\Omega_{ccb}$, $\Omega_{cbb}$ and Omega_bbb, together with QCD-stable baryons containing top quarks. Our NNLO MRS results undershoot lattice QCD determinations by 125-175 MeV, with the fractional difference decreasing as $1/m_Q$ - the pattern expected from the neglected $\mathcal{O}(1/m_Q)$ corrections, which makes the deficit a controlled feature of the truncation rather than an anomaly. 
Extending the framework to unequal-mass fully-heavy tetraquarks, we determine the critical heavy-to-light mass ratio required for binding and map binding energies across the mass-ratio landscape, with direct bearing on the fully-heavy exotic candidates reported at the LHC. Based on arXiv:2607.08817.

Interacting quark matter under imaginary rotation

• Tudor Pătuleanu (Institut Denis Poisson)

Room: Amphi Kastler Lattice QCD simulations with real rotation suffer from the sign problem, which can be avoided by introducing an imaginary angular velocity. Motivated by this, we study interacting quark matter in the linear sigma model under imaginary rotation, $\Omega = i\Omega_I$, and determine its thermodynamic properties and phase diagram. We show that the fractalization previously identified for free massless fermions persists in the interacting massive case and has nontrivial consequences for the phase structure in the far-field limit. For rational frequencies, $\nu = \beta \Omega_I / (2 \pi) = \mathsf{p} / \mathsf{q}$, the system exhibits ninionic statistics, interpolating between fermionic and bosonic behavior according to the parity of $\mathsf{k} = \mathsf{p} + \mathsf{q}$. On the rotation axis, we identify crossover, first-order, and no-transition regimes depending on $\nu$, and we further study how the phase structure evolves at intermediate distances from the rotation axis toward the far-field regime. Finally, we investigate the moment of inertia and compare the resulting behavior with lattice QCD studies of matter under imaginary rotation.

The dead cone effect across heavy-quark jet flavors

• Redamy PEREZ-RAMOS (IPSA/LPTHE)

Room: Amphi Kastler We present a unified overview of recent progress in the study of QCD radiation in heavy-quark jets, focusing on the dead-cone effect. Using precision data from LEP at ~91.2 GeV, we demonstrate strong momentum-space suppression in charm and bottom quark jets, supported by Monte Carlo simulations with Pythia8, and provide a quantitative interpretation within the Modified Leading Logarithmic Approximation (MLLA) of perturbative QCD. We then extend the analysis to top-quark jets at ~1 TeV, where finite lifetime effects and decay radiation introduce new conceptual challenges. A new method is presented to isolate the top-quark dead cone by separating production and decay radiation, and it is validated at both parton and hadron level using Pythia8. Together, these results establish a coherent framework for testing QCD radiation dynamics across all three heavy quarks.

Exploring the nucleon structure via Deeply Virtual Compton Scattering

• Juan Sebastian Alvarado Galeano

Room: Amphi Kastler Generalized parton distributions (GPDs) are nucleon structure functions encoding longitudinal momentum and transverse position distributions of its constituent partons. In the zero-momentum-transfer limit ($t\rightarrow 0$), they provide access to fundamental mechanical and spin properties, in particular, the nucleon internal pressure distribution. Experimentally, GPDs can be probed through the electroproduction of a real photon via Deeply Virtual Compton Scattering (DVCS), and more generally, through the electroproduction of a dilepton pair via Double Deeply Virtual Compton Scattering (DDVCS). Using data from the CLAS12 spectrometer at Jefferson Lab, we report new Beam-Spin Asymmetry measurements of DVCS on the proton at small momentum transfer. Enabled by machine-learning techniques, these results extend the accessible kinematic range toward the $t\rightarrow 0$ limit, provide precise measurements over a broad kinematic range, and help constraining the proton’s pressure distribution through global fits. Finally, prospective measurements of DDVCS are discussed in the context of forthcoming experiments using polarized electron beams at Jefferson Lab and the future Electron-Ion Collider, highlighting their sensitivity to different GPD contributions and parametrizations.

Flash talk Room: Amphi Kastler

Final Remarks Room: Amphi Kastler