Conveners
WG2 Small-x, diffraction and vector mesons
- Michael Pitt (CERN)
WG2 Small-x, diffraction and vector mesons
- Michael Pitt (CERN)
WG2 Small-x, diffraction and vector mesons
- Cristovao Fernandes Vilela
WG2 Small-x, diffraction and vector mesons
- Cristovao Fernandes Vilela
WG2 Small-x, diffraction and vector mesons
- Cristovao Fernandes Vilela
WG2 Small-x, diffraction and vector mesons
- Cristovao Fernandes Vilela
WG2 Small-x, diffraction and vector mesons
- Jani Penttala (UCLA)
WG2 Small-x, diffraction and vector mesons
- Michael Pitt (CERN)
WG2 Small-x, diffraction and vector mesons
- Jani Penttala (UCLA)
WG2 Small-x, diffraction and vector mesons
- Jani Penttala (UCLA)
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Nazar Burmasov (Joint Institute for Nuclear Research)05/05/2026, 09:00WG2 Small-x, Diffraction and Vector MesonsTalk
We present new measurements from the ALICE experiment on exclusive processes in ultra-peripheral PbโPb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.36$ TeV. The coherent photoproduction of ${\rm J} / \psi$ and $\psi({\rm 2S})$ is measured differentially in rapidity to probe nuclear gluon distributions at low Bjorken-$x$ $\sim$ $10^{-2}$. A significant suppression relative to the impulse...
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Dukhishyam Mallick (Istituto Nazionale di Fisica Nucleare)05/05/2026, 09:20WG2 Small-x, Diffraction and Vector MesonsTalk
Ultrarelativistic heavy-ion collisions generate extremely strong electromagnetic fields that can induce photonuclear reactions. These processes have been extensively studied in ultraperipheral collisions (UPCs), where the impact parameter is larger than twice the nuclear radius. Recently, coherent J/$\psi$ photoproduction has also been observed in nucleus--nucleus (A--A) collisions with...
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Agnieszka Ogrodnik (Institute of Nuclear Physics Polish Academy of Sciences)05/05/2026, 09:40WG2 Small-x, Diffraction and Vector MesonsTalk
In ultra-relativistic heavy-ion collisions, the Lorentz-contracted electromagnetic fields of the ions generate intense quasi-real photon fluxes. These can interact with photons emitted by the oncoming nucleus, or with the nucleus itself, either directly in inelastic processes or diffractively via pomeron exchange. Diffractive photo-nuclear processes can produce exclusive vector mesons that...
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Shuai Yang (South China Normal University)05/05/2026, 10:00WG2 Small-x, Diffraction and Vector MesonsTalk
The study of $\rm{J}/\psi$ photoproduction in ultra-peripheral collisions (UPCs) offers a powerful probe of gluon dynamics in heavy nuclei. In UPCs, photons can interact with the nucleus coherently (involving the entire nucleus) or incoherently (with individual constituents). While coherent processes provide insight into the average gluon density, incoherent photoproduction is uniquely...
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Pranjal Verma (IIT Madras)05/05/2026, 10:20WG2 Small-x, Diffraction and Vector MesonsTalk
Photon-induced vector meson production in ultraperipheral heavy-ion collisions (UPCs) offers a unique and powerful probe of the gluon distribution in nuclei. The $\phi$ meson, with its mass around 1 GeV, lies at the boundary of hard scales between the perturbative and nonperturbative QCD regimes, making it uniquely suited to probe the transition between these two domains. Similarly, coherent...
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Benjamin Gilbert (Lawrence Livermore National Laboratory)05/05/2026, 11:15WG2 Small-x, Diffraction and Vector MesonsTalk
In ultra-peripheral collisions (UPCs), emitted photons may participate in a hard-scattering process with partons within the struck nucleus, providing a clean, energetic probe of its parton distributions. This talk presents measurements of jet production in UPCs performed with the ATLAS detector using high-statistics 2018 Pb+Pb data. Events are selected using requirements on jet production,...
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Balasz Kovacs (MIT)05/05/2026, 11:35WG2 Small-x, Diffraction and Vector MesonsTalk
Open heavy-flavor production in ultraperipheral collisions (UPCs) enables the study of cold nuclear matter over a wide range of momentum transfers $Q$ and parton momentum fractions $x$, without significant final-state effects. In this talk we present the final results for the first measurement of $\mathrm{D}^0$ photoproduction in heavy-ion UPCs using data collected by the CMS experiment during...
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Mr Nicholas Jindal (The Ohio State University)05/05/2026, 11:55WG2 Small-x, Diffraction and Vector MesonsTalk
Dielectron production can occur in ultraperipheral heavy ion collisions (UPCs) via the Breit-Wheeler process, in which the quasi-real photons from the heavy ion-induced electromagnetic fields interact to produce a low transverse momentum dielectron pair. This production is sensitive to the charge radius and nuclear shape of the atomic nucleus sourcing the photons. By comparing the momentum...
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Xihe Han05/05/2026, 12:15WG2 Small-x, Diffraction and Vector MesonsTalk
Ultra-peripheral heavy-ion collisions provide a clean environment for studying photon--nucleus and photon--nucleon interactions. We present measurements of $\phi$-meson production in ultra-peripheral Au+Au collisions at $\sqrt{s_{NN}} = 200$~GeV with the STAR experiment at RHIC, performed via the $\phi \rightarrow K^{+}K^{-}$ decay channel. Those are the first RHIC studies of coherent and...
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Mrs Alexandra Ridzikova (Czech Technical University in Prague)05/05/2026, 12:35WG2 Small-x, Diffraction and Vector MesonsTalk
We present predictions for diffractive photoproduction of $\rho^0$ and $J/\psi$ vector mesons in ultra-peripheral oxygenโoxygen and neonโneon collisions using the energy-dependent hotspot model.
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A striking prediction of this model is that the energy dependence of the incoherent cross section provides a clear signature of saturation effects: the cross section rises with energy, reaches a... -
Benjamin Guiot (Universidad federico santa maria)05/05/2026, 14:30WG2 Small-x, Diffraction and Vector MesonsTalk
Quarkonium-pair production is a rich observable, providing valuable insights into gluon TMDs, double parton scattering, and, of course, the production mechanism itself. While direct production has been frequently studied, here we investigate the contribution from heavy-quark fragmentation, including, in particular, $D_{Q\to H_1 H_2}$ for the fragmentation of a heavy quark into two...
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Prof. M.Beatriz Gay Ducati (UFRGS)05/05/2026, 14:50WG2 Small-x, Diffraction and Vector MesonsTalk
Perturbative Quantum Chromodynamics describes the strong interaction among quarks and gluons. Specifically, the gluons are supposed to recombine at low momentum (low x) for extreme conditions, onseting saturation to restore unitarity. This challenging phenomenon is faced experimentally with peripheral and ultraperipheral production of heavy mesons, J/Psis and Upsilons, mostly gluons dependent....
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Michael Fucilla05/05/2026, 15:10WG2 Small-x, Diffraction and Vector MesonsTalk
Based on: https://arxiv.org/abs/2601.04142
We present the first complete next-to-leading-order calculation of the impact factors for hadroproduction of the ${}^1S_0^{[1]}$, ${}^1S_0^{[8]}$, and ${}^3S_1^{[8]}$ NRQCD states
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within the BFKL formalism. We complete the recent virtual-correction computation presented in \href{https://doi.org/10.1007/JHEP12(2024)129}{JHEP 12 (2024) 129} by that... -
Dr Yu Shi (Ecole Polytechnique, CNRS)05/05/2026, 15:30WG2 Small-x, Diffraction and Vector MesonsTalk
We develop a unified resummation framework for heavy-meson pair photoproduction that treats soft-gluon radiation in a massive scheme for $|q| \lesssim m_Q$ and is consistent with the massless limit $m_Q \ll |q|$, where $q$ denotes the transverse momentum of the pair and $m_Q$ the quark mass. This framework describes the full correlation regime $|q| \ll |P|$, with $P$ the pair's relative...
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Hendrik Roch (University of Jyvรคskylรค)05/05/2026, 16:30WG2 Small-x, Diffraction and Vector MesonsTalk
Diffractive vector meson production provides a powerful probe of gluon saturation and the spatial structure of small-x gluons. Within the Color Glass Condensate (CGC) framework, it is sensitive to both nonlinear dynamics and event-by-event fluctuations in the proton wave function. HERA data, particularly for ${J/\psi}$ photoproduction, suggest that the gluonic radius of the proton is smaller...
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Wenbin Zhao05/05/2026, 16:50WG2 Small-x, Diffraction and Vector MesonsTalk
Dihadron angular correlations in forward protonโproton and protonโnucleus collisions offer a sensitive probe of gluon saturation effects, where both gluon saturation and parton shower dynamics contribute to the observed de-correlation between back-to-back hadron pairs. In this talk, we employ the Color Glass Condensate (CGC) framework to conduct a detailed numerical investigation of dihadron...
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Ishita Ganguli (AGH University of Krakow)05/05/2026, 17:10WG2 Small-x, Diffraction and Vector MesonsTalk
We investigate gluon saturation signals in photonโhadron transverse energyโenergy correlation (TEEC), along with the ordinary azimuthal correlations, in the forward rapidity region for protonโproton and protonโlead collisions, in the context of the HL-LHC upgrades, in particular the FoCal detector of ALICE which will cover 3.8 < ฮท < 5.1 and the ATLAS detector with the extended coverage of |ฮท|...
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Prithwish Tribedy (Brookhaven National Laboratory)05/05/2026, 17:30WG2 Small-x, Diffraction and Vector MesonsTalk
Heavy vector-meson photoproduction is a premier tool for imaging nuclear gluon distributions, traditionally via the momentum-transfer ($t$) dependence of exclusive cross sections. We show that in ultra-peripheral heavy-ion collisions (UPCs) the $J/\psi$ spin/decay angular structure provides a complementary handle for gluon tomography, enabled by the UPC ``two-source'' interferometer and...
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Mr imanol corredoira (Universidade de Santiago de Compostela / IGFAE)05/05/2026, 17:50WG2 Small-x, Diffraction and Vector MesonsTalk
In heavy-ion collisions, collective phenomena in the hot and dense medium known as the QuarkโGluon Plasma (QGP) are probed through measurements of mean transverse momentum and azimuthal particle correlations. Similar correlation patterns observed in small collision systems raise questions about their origin, involving either final-state collective effects or initial-state parton correlations...
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Xuanbo Tong05/05/2026, 18:10WG2 Small-x, Diffraction and Vector MesonsTalk
In recent years, energy correlators have attracted renewed interest as powerful probes of QCD dynamics. Extending this concept to nucleon structure, nucleon energy correlators (NECs) offer a new avenue for imaging partonic dynamics through correlations between initial-state partons and energy flow in the target fragmentation region. In this talk, I will present an investigation of NECs at...
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Truong My Hau Le (Jagiellonian University)06/05/2026, 09:20WG2 Small-x, Diffraction and Vector MesonsTalk
Many experiments have provided possible hints of gluon saturation, including geometric scaling in deep inelastic scattering (DIS) at HERA, the suppression of forward particle yields in d+Au collisions relative to p+p collisions at RHIC, and the suppression of away-side peaks in di-hadron correlations at forward rapidities in proton-nucleus collisions at RHIC and the LHC. Previous studies...
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Carlisle Casuga (University of Jyvรคskylรค), Swaleha Mulani (University of Jyvaskyla)06/05/2026, 09:40WG2 Small-x, Diffraction and Vector MesonsTalk
We constrain the non-perturbative initial condition to the next-to-leading order (NLO) Balitsky-Kovchegov (BK) equation by comparing NLO DIS calculations to both the HERA total inclusive cross section and the charm quark production datasets. This global approach is done through our well-tested Bayesian framework, used in previous analysis [1] as well. The cross sections are calculated by...
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Fredrick Olness (SMU)06/05/2026, 10:00WG2 Small-x, Diffraction and Vector MesonsTalk
A central objective of the SURGE Collaboration is to investigate dense nuclear matter in the small-x kinematic region. The dipole model within the Color Glass Condensate (CGC) effective field theory provides a powerful framework for describing these phenomena. We are developing an efficient computational framework to evaluate and fit small-x data within a global analysis setting. Ongoing...
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Magnus Bertilsson06/05/2026, 11:00WG2 Small-x, Diffraction and Vector MesonsTalk
Predictions for the inclusive DIS total cross section at small $x$ are commonly obtained using the forward elastic scattering amplitude in the dipole picture. However, the usual dipole picture assumes an asymptotically large photon-proton center-of-mass energy $W$, such that the phase space of the produced partonic system at the unitarity cut remains unconstrained. In this work, we move away...
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Rojae Mighty06/05/2026, 11:20WG2 Small-x, Diffraction and Vector MesonsTalk
Understanding the structure of protons and nuclei in terms of quarks and gluons is one of the key goals in science. Results from RHIC suggest the existence of a new state of matter known as gluon saturation. The idea is, at high energies, gluons, due to their self-interactions multiply rapidly; however, when their density becomes very large, recombination effects set in, leading to saturation...
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Samuel Corey (The Ohio State University)06/05/2026, 11:40WG2 Small-x, Diffraction and Vector MesonsTalk
In ultraperipheral collisions, the invariant mass spectrum of $\pi^+ \pi^-$ pairs is very complex due to the numerous production channels and intermediate states. The most dominant component of this spectrum is $\gamma A \rightarrow \rho^0 (770) \rightarrow \pi^+ \pi^-$ production, and the invariant mass region surrounding the $\rho^0 (770)$ is well-described with the inclusion of photonuclear...
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Piotr Kotko (AGH University of Krakow)06/05/2026, 12:00WG2 Small-x, Diffraction and Vector MesonsTalk
We discuss the potential of the recently proposed LH$\mu$C (anti-muon-proton collider at CERN) in exploring both the perturbative and non-perturbative aspects of QCD. With the access to an unprecedentedly low Bjorken $x$, as low as $10^{-7}$ at perturbative virtualities $Q^2\simeq1$ GeV$^2$, the LH$\mu$C will allow to study the properties of protons and nuclei in the gluon saturation regime,...
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Benedetta Bernardini06/05/2026, 12:20WG2 Small-x, Diffraction and Vector MesonsTalk
I will present new results on the inclusion of small-x resummation in the computation of the production of a Higgs boson, differential in rapidity and transverse momentum. The implementation in the HELL framework is discussed, as well as phenomenological implications for LHC and future high-energy colliders.
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Piotr Korcyl (Jagiellonian University)06/05/2026, 14:30WG2 Small-x, Diffraction and Vector MesonsTalk
High-energy QCD evolution beyond leading order suffers from instabilities driven by large collinear logarithms. We present a framework, consistent with the standard high-energy operator product expansion (OPE), that restores perturbative stability order by order. The method involves a change of basis in the space of high-energy operators, which modifies both the evolution kernel and the...
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Guillaume Beuf (National Centre for Nuclear Research (NCBJ), Warsaw)06/05/2026, 14:50WG2 Small-x, Diffraction and Vector MesonsTalk
In recent years, numerous studies have aimed at improving the precision of the theoretical description of the nonlinear QCD regime of gluon saturation in high-energy collisions, in order to match the precision of the data coming from the LHC and the future EIC. In particular, NLO QCD corrections have been calculated for many high-energy processes sensitive to gluon saturation.
In most of...
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Jan Cepila (Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering)06/05/2026, 15:10WG2 Small-x, Diffraction and Vector MesonsTalk
In this talk a solution of the target-rapidity Balitsky-Kovchegov (BK) equation at the next-to-leading order (NLO) level is presented. At first, a version of the BK equation that includes only most important collinear part of the NLO contribution is used and the solution with the complete impact-parameter dependence is shown, including the orientation of the dipole with respect to the...
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Florian Cougoulic (Jagiellonian University)06/05/2026, 15:30WG2 Small-x, Diffraction and Vector MesonsTalk
To evaluate the high-energy dependence of the dipole or transverse momentum distributions (TMDs) within the color glass condensate framework, one relies on evolution equations such as the JIMWLK equation, or its large-Nc limit the BK equation.
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It has been observed that the discrepancy between solutions for the dipole from the BK equation and the JIMWLK equation is less than expected from... -
Ada Polizzi (Istituto Nazionale di Fisica Nucleare)06/05/2026, 16:30WG2 Small-x, Diffraction and Vector MesonsTalk
A general framework for the description of semi-hard scattering amplitudes in perturbative Quantum Chromodynamics (pQCD) is presented, based on the use of the next-to-leading order eigenfunctions of the BalitskyโFadinโKuraevโLipatov (BFKL) kernel constructed by Chirilli and Kovchegov. Formal aspects related to the consistency with the corresponding formulation employing leading-order BFKL...
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Pyry Runko (University of Jyvรคskylรค)06/05/2026, 16:50WG2 Small-x, Diffraction and Vector MesonsTalk
We compute diffractive structure functions from Wilson line configurations whose energy evolution is given by the JIMWLK equation. We use a JIMWLK evolution setup that has already been constrained with exclusive vector meson production data from HERA. Our results can be compared to HERA measurements and also extended to heavy nuclei. In particular we can calculate predictions for the nuclear...
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Marek Tasevsky (Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic)06/05/2026, 17:10WG2 Small-x, Diffraction and Vector MesonsTalk
Although the QCD instanton has been intensively searched for in several experiments, and is currently being searched at LHC, it has not so far been observed. In 2208.14089 we study the possibility to observe heavy ($M_{\rm inst}>$ 60 GeV) QCD instantons at the LHC in the diffraction mode, i.e. in events with one or two tagged leading protons which are accompanied by large rapidity gaps. The...
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Tobias Toll (Indian Institute of Technology Delhi)06/05/2026, 17:30WG2 Small-x, Diffraction and Vector MesonsTalk
Inclusive diffraction in eA is seen as a first year measurement of saturation physics at the electron-ion collider. Therefore it is crucial to be able to simulate and generate inclusive diffractive events at small momentum fractions. This new version of Sartre is the first event generator for inclusive diffraction at small x in electron-ion collisions. Sartre calculates the amplitudes in the...
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Abhiram Kaushik Badrinarayanan (University of Jyvaskyla)06/05/2026, 17:50WG2 Small-x, Diffraction and Vector MesonsTalk
We report on our recent work [1] where we compute the $q\bar q g$ contribution to the diffractive structure functions in high-energy deep inelastic scattering (DIS). The obtained result corresponds to a self-contained, finite part of the next-to-leading-order (NLO) contribution to the diffractive cross section. Previous phenomenological applications have included this contribution only in the...
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Paul Caucal (SUBATECH, Nantes Universitรฉ, IN2P3/CNRS)06/05/2026, 18:10WG2 Small-x, Diffraction and Vector MesonsTalk
Single-inclusive particle production in Deep Inelastic Scattering (DIS) provides a powerful probe of the three-dimensional partonic structure of hadrons and nuclei. While most small-x studies focus on the current fragmentation region of DIS, we investigate particle production in the target fragmentation region, which is naturally described in terms of fracture functions.
Focusing on...
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Adriรกn Romero Gonzรกlez (IGFAE - Universidade de Santiago de Compostela)07/05/2026, 09:20WG2 Small-x, Diffraction and Vector MesonsTalk
We study non-eikonal effects on dijet production in nuclear DIS at small x, working within the Color Glass Condensate. We include those power-supressed corrections in the high-energy limit coming from the relaxation of the shockwave approximation, while neglecting transverse components of the target fields and their dynamics. With this approximation we provide, to all orders in the length of...
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Yossathorn Tawabutr (Chulalongkorn University)07/05/2026, 09:40WG2 Small-x, Diffraction and Vector MesonsTalk
We apply the valence quark model with corrections coming from gluon emissions to constrain the moderate-energy behavior of the polarized dipole amplitudes responsible for the quark and gluon helicity inside the proton at small Bjorken $x$. Our model radically reduces the number of free parameters associated with the moderate-energy initial conditions to the small-$x$ helicity evolution,...
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Giovanni Antonio Chirilli (National Centre for Nuclear Research (NCBJ), Warsaw)07/05/2026, 10:00WG2 Small-x, Diffraction and Vector MesonsTalk
Deep-inelastic scattering at small Bjorken-$x$ is best studied in the dipole model, where the virtual photon emitted by the lepton projectile fluctuates into a quark--antiquark pair that propagates through the dense hadronic target. In this framework, the cross section is given as a convolution of an impact factor and target matrix elements of Wilson lines along nearly lightlike trajectories....
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Jules Favrel (National Centre for Nuclear Research (NCBJ), Warsaw, PL)07/05/2026, 10:20WG2 Small-x, Diffraction and Vector MesonsTalk
We present next-to-leading order (NLO) corrections to next-to-eikonal (NEik) quark background contributions to DIS structure functions. Among NEik corrections, $t$-channel quark exchanges provide the lowest order contributions in $\alpha_s$, and can be represented as insertions of the quark background field of the target. At NLO, we compute NEik
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corrections induced by both quark and gluon... -
Kacper Goslawski (National Centre for Nuclear Research, Warsaw), jules Favrel (National Centre for Nuclear Reseach, Warsaw, PL)07/05/2026, 11:15WG2 Small-x, Diffraction and Vector MesonsTalk
We consider dijet production in deep inelastic scattering at small x, on a purely gluonic unpolarized target. Starting from earlier results obtained at next-to-eikonal accuracy in the high-energy limit, we perform the expansion in the back-to-back dijet limit, at next-to-leading power (NLP) accuracy. We rewrite our results in the language of transverse-momentum-dependent (TMD) factorization,...
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Mirja Tevio (National Center for Nuclear Research (NCBJ), Warsaw)07/05/2026, 11:35WG2 Small-x, Diffraction and Vector MesonsTalk
We use the background field formalism to calculate NLO corrections to a quark transverse momentum dependent parton distribution function (TMD) in the projectile light-cone gauge, i.e. $A^+=0$ for a left-moving target.
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We calculate the full result using two different ways, corresponding to different prescriptions for handling the light-cone singularity: the MandelstamโLeibbrandt and a family... -
Jamal Jalilian-Marian (Baruch College)07/05/2026, 11:55WG2 Small-x, Diffraction and Vector MesonsTalk
Single inclusive hadron production in Deep Inelastic Scattering (SIDIS) is one of the most promising processes in which to look for signatures of color glass condensate (CGC), a dense state of gluons in a proton/nucleus that is believed to exist at small $x$. While there have been strong hints of CGC dynamics observed at HERA, RHIC and the LHC, an unambiguous interpretation has eluded the...
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Andrea Simonelli (Istituto Nazionale di Fisica Nucleare)07/05/2026, 12:15WG2 Small-x, Diffraction and Vector MesonsTalk
The relationship between Regge factorization of amplitudes and the CollinsโSoperโSterman factorization of hadronic cross sections is explored. Aiming at a unified description of the treatment of rapidity divergences and the high-energy asymptotic behavior of scattering amplitudes, novel insights into the extension of $k_T$-factorization beyond leading-log (LL) accuracy are revealed. In...
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Paul Caucal (SUBATECH, Nantes Universitรฉ, IN2P3/CNRS)07/05/2026, 12:35WG2 Small-x, Diffraction and Vector MesonsTalk
Semi-inclusive deep inelastic scattering (SIDIS) with a hadron measured in the final state is a well-established observable to probe the three-dimensional momentum structure of nucleons and nuclei, in particular at small Bjorken $x$ where the cross-section factorizes in terms of a sea quark transverse momentum (TMD) distribution [1]. However, to extract TMDs from hadron measurements, one needs...
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