Workshop on parton distribution functions in the EIC era

16 Jun 2025, 09:30 → 18 Jun 2025, 18:00 Asia/Taipei

Meeting Room, 5F, New Phys Bldg (Institute of Physics, Academia Sinica)

C.-J. David Lin (Institute of Physics, National Yang Ming Chiao Tung University), Wen-Chen Chang (Institute of Physics, Academia Sinica)

The electron-ion collider will significantly enhance our understanding of hadron structure.  This workshop aims to bring together experts in experiments, phenomenology and lattice calculations that are relevant to this subject.  In addition to invited presentations, we can accommodate a few contributed talks with priority given to junior reseachers.

Registration deadline: 23h59 the 8th of June 2025 Taiwan time.  
Abstract submission deadline: 23h59 the 31st of May 2025 Taiwan time.  

Invited speakers include

   Yang-Ting Chien (Georgia State U)

 

   Yuji Goto (RIKEN)

 

   Tanja Horn (Catholic University of America)

 

   Tie-Jun Hou (University of South China)

   Chia-Yu Hsieh (Academia Sinica)

 

   Kyungseon Joo (University of Connecticut)

 

   Huey-Wen Lin (Michigan State University)

 

   Swagato Mukherjee (Brookhaven National Laboratory)

   Manuel Schneider (National Yang Ming Chiao Tung University)

 

   Ross Young (University Adelaide)

 

   Chien-Peng Yuan (Michigan State University)

 

   James Zanotti (University of Adelaide)

 

Monday 16 June

1 Deeply virtual exclusive processes

The study of Deeply Virtual Exclusive Processes (DVEP) provides crucial insights into the three-dimensional structure of the nucleon by probing Generalized Parton Distributions (GPDs). These GPDs offer a comprehensive description of the spatial distribution of quarks and gluons within the nucleon and their contributions to its overall properties, including spin and mass. Key reactions, such as Deeply Virtual Compton Scattering (DVCS), Time-like Compton Scattering (TCS), and Deeply Virtual Meson Production (DVMP) of various mesons, are investigated. These processes enable nucleon tomography, help unravel the nucleon spin puzzle by constraining Generalized Parton Distributions (GPDs), and significantly enhance our understanding of Quantum Chromodynamics (QCD) and the emergent properties of hadrons. In this talk, recent results from CLAS12 at Jefferson Lab will be presented, and the potential program with the future Electron-Ion Collider will be discussed.

Speaker: Prof. Kyungseon Joo (University of Connecticut)

2 Gravitational form factors of the Goldstone bosons from chiral effective models

In this talk, we discuss the properties of the gravitational form factors (GFFs), obtained from the second Mellin moment of the pion and kaon generalized parton distributions (GPDs) within the framework of the nonlocal chiral quark model. Our results demonstrate that explicit chiral symmetry breaking significantly influences quark GPDs in kaon at large skewness, leading to substantial modifications of the D-term compared to the exact chiral limit case. We examine the leading-order evolution of the GPDs and GFFs, and compare our results with predictions of other effective model and Lattice QCD studies. Additionally, we explore the parity-odd GFFs of the Goldstone bosons and their physical interpretations.

Speaker: Dr Hyeon-Dong Son (Inha University)

11:00 Coffee

3 Jet charge and one-jettiness at the EIC

We discuss the simultaneous measurements of jet electric charge of the jet region as defined in the one-jettiness of DIS events. On one hand, the jet charge allows for enhanced flavor separation of collinear parton distribution functions (PDFs) or helicity PDFs. On the other hand, the jet charge distributions as constrained by one-jettiness values probe flavor dynamics in the hadronization process. We derive factorized expressions of the doubly differential cross section and demonstrate the sensitivity of the jet charge to flavor and energy flow dependence of hadronization.

Speaker: Prof. Yang-Ting Chien (Georgia State University)

12:30 Lunch

4 Spin physics at PHENIX/sPHENIX

We have been studying the origin of the spin inside the proton using polarized proton collisions by the RHIC accelerator at Brookhaven National Laboratory in the United States. The proton spin cannot be explained by the spin of the quark inside the proton alone, but must be explained by the addition of the spin of the gluon and the orbital motion of the quark and the gluon inside the proton, which is not easy to measure. In this talk, we will present the results measured by the PHENIX experiment and the prospects for the results obtained by the sPHENIX experiment, which is currently underway.

Speaker: Prof. Yuji Goto (RIKEN)

5 TBA

Speaker: Prof. Tie-Jun Hou (University of South China)

16:00 Coffee

6 Momentum, structure, and forces in the nucleon from lattice QCD

Lattice QCD is advancing our understanding of nucleon structure across a wide range of observables, tied together by a common goal: resolving how momentum and forces are distributed among quarks and gluons. I will begin with recent high-precision determinations of the isovector axial, scalar, and tensor charges, where a comprehensive treatment of systematic uncertainties is enabling meaningful comparisons with experiment. Turning to the gluon momentum fraction, I will highlight progress in nonperturbative renormalisation and the treatment of quark-gluon mixing—essential for satisfying the QCD momentum sum rule. These developments connect naturally to the broader physics of generalised parton distributions and impact-parameter densities, where off-forward Compton amplitudes provide a new handle on power corrections and spatial structure. I will conclude with a recent breakthrough: the extraction of twist-3 matrix elements encoding the transverse colour-Lorentz force acting on a struck quark in deep inelastic scattering. This force, reaching magnitudes comparable to the weight of ten elephants, offers a striking new perspective on confinement at the subnucleonic scale.

Speaker: Prof. James Zanotti (The University of Adelaide)

Tuesday 17 June

7 Pion-induced Drell-Yan muon pair production on various nuclear targets at COMPASS

The partonic structure of the pion remains poorly understood due to the lack of direct pion targets. Current global fits of the pion parton distribution functions (PDFs) rely primarily on decades-old fixed-target Drell-Yan experiments (NA10 and E615), which are mostly sensitive to valence quarks. The CERN COMPASS experiment has provided new data by measuring Drell-Yan production using a 190 GeV/c π− beam incident on a transversely polarized NH3 target, as well as nuclear alumina and tungsten targets, in 2015 and 2018. The use of the light NH3 target offers the advantage of reduced nuclear effects in the extraction of pion PDFs. We report differential cross sections for pion-induced Drell-Yan production in the kinematic ranges of Feynman-xF = −0.2 to 0.9 and transverse momentum pT=0.0 to 3.6 GeV/c. In this talk, preliminary cross-section results will be presented and compared with fixed-order QCD calculations using various pion PDF sets. The kinematic dependence of nuclear effects in Drell-Yan production will also be examined by comparing cross sections obtained from the three different targets.

Speaker: Dr Chia-Yu Hsieh (Academia Sinica, Taiwan)

11:00 Coffee

8 Pion and kaon structure - experimental overview (EIC & JLab)

Pions and kaons are, along with protons and neutrons, the main building blocks of nuclear matter. They are connected to the Goldstone modes of dynamical chiral symmetry breaking, the mechanism thought to generate nearly all hadron mass in the visible universe. The distribution of the fundamental constituents, the quarks and gluons, is expected to be different in pions, kaons, and nucleons. However, experimental data are sparse. As a result, there has been persistent doubt about the behavior of the pion's valence quark structure function at large Bjorken-x and virtually nothing is known about the contribution of gluons. Experiments at 12 GeV JLab using the Sullivan reaction process may provide insight and contribute to the resolution of the former. The Electron-Ion Collider with an acceptance optimized for forward physics could provide access to structure functions over a larger kinematic region. This would allow for measurements testing if the origin of mass is encoded in the differences of gluons in pions, kaons, and nucleons, and measurements that could serve as a test of assumptions used in the extraction of structure functions and the pion and kaon form factors. Measurements at an EIC would also allow to explore the effect of gluons at high x. In this talk we will discuss the prospects of such measurements.

Speaker: Prof. Tanja Horn (Catholic University of America)

12:30 Lunch

9 Advancing nucleon and pion parton distributions with lattice QCD: insights and impact on global analyses

Recent advances in lattice QCD (LQCD), particularly large-momentum effective theory (LaMET) and related approaches, have enabled direct access to the Bjorken-$x$ dependence of hadron structure, going beyond LQCD's previous limitation to a few moments of distributions. These techniques open the door to first-principles calculations of parton distribution functions (PDFs) across a wide kinematic range, including regions poorly constrained by experimental data. In this talk, I will highlight recent progress in determining nucleon and pion PDFs from LQCD, and demonstrate how incorporating these results into global QCD analyses can enhance our understanding of parton structure and complement experimental efforts in key kinematic regimes.

Speaker: Prof. Huey-Wen Lin (Michigan State University)

10 Compton amplitudes and nucleon structure from lattice QCD

The Compton amplitude offers a unifying lens through which to explore the structure of hadrons, connecting deep-inelastic phenomena with low-energy sum rules and nonperturbative dynamics. In this talk, I will present a series of lattice QCD investigations that leverage the Feynman-Hellmann relation to access this amplitude directly, enabling a systematic study of structure function moments, power corrections, and twist expansions. By combining formal developments with numerical results, we shed light on both spin-independent and spin-dependent sectors, including the elusive subtraction function, parity-violating observables, and higher-twist contributions. These results highlight the growing role of the Compton amplitude as a precision tool in hadron structure and a bridge between lattice QCD and phenomenology.

Speaker: Prof. Ross Young (University of Adelaide)

16:00 Coffee

11 Lattice QCD calculation of the first and second moments of the kaon distribution amplitude

The kaon light-cone distribution amplitude (LCDA) is a crucial quantity in understanding the structure of hadrons. In this work, we use lattice quantum chromodynamics (LQCD), a powerful tool for calculating non-perturbative quantities. Since LQCD calculations are performed in Euclidean space, we apply the heavy-quark operator product expansion (HOPE) to connect light-cone parton dynamics with calculations in Euclidean space. This approach entails an OPE analysis of hadronic amplitudes in Euclidean space through the insertion of two local quark bilinears with a fictitious, valence heavy quark. We present the status of our numerical calculation for the first and second Mellin moments of the kaon LCDA obtained through the HOPE framework, advancing our understanding of parton distributions in mesons.

Speaker: Mr Sheng Pin Chang (Institute of Physics, National Yang Ming Chiao Tung University)

18:00 Banquet

Wednesday 18 June

12 Unveiling the Strongest Force in Nature through EIC and Lattice QCD

The Electron-Ion Collider (EIC) aims to explore the mysterious internal structure of protons by precisely probing their quark and gluon constituents through experiments. But observing these particles is just the first step—truly understanding them requires detailed insights from the theory known as Quantum Chromodynamics (QCD), which governs the behavior of these tiny building blocks. Lattice QCD, a powerful computational method based on first-principle QCD, offers the essential framework to interpret experimental findings, enabling us to decode the complex interactions and structures observed by the EIC. In this talk, I will highlight how lattice QCD bridges experimental results with fundamental theory, transforming experimental knowledge of protons into genuine understanding.

Speaker: Prof. Swagato Mukherjee (Brookhaven National Laboratory)

13 Extraction of the Collin-Soper kernel on the lattice using complex directional Wilson lines

The TMD soft function may be modeled by formulating the Wilson line in terms of auxiliary 1-dimensional fermion fields with complex directional vectors in Euclidean space. Using this approach we present a method for obtaining both the TMD soft function and the Collins-Soper kernel from lattice QCD. Our computation takes place in the region of the lattice that corresponds to the “spacelike” region in Minkowski space, which corresponds to the Collins definition of the Soft function. The matching of our result to the Collins soft function is achieved through the mapping of the auxiliary field directional vector to the Wilson line rapidity. I present some exploratory numerical results of our lattice calculation, and discuss the methodology employed.

Speaker: Dr Wayne Morris (NYCU)

11:00 Coffee

14 Direct calculation of parton distribution fucntions with tensor network states

The EIC will measure the structure of hadrons at a new level of precision, requiring the support of a robust theoretical description. Universal properties of nuclei can be described by Parton distribution functions (PDFs). They provide insights into the non-perturbative internal structure of bound states. Calculating PDFs from first principles involves evaluating matrix elements with a Wilson line in a light-cone direction. This poses significant challenges for Monte Carlo methods in Euclidean formulation of lattice gauge theory, where the light cone cannot be directly accessed. In contrast, the PDF can, in principle, be calculated directly from light-cone matrix elements in the Hamiltonian formalism. We introduce a strategy to obtain the PDFs directly in Minkowski space with tensor network states, and apply it to the Schwinger model. We present the PDF for different fermion masses in the continuum limit. This shows the feasibility of tensor networks for dynamical calculations in gauge theories and represents a first step towards such computations for QCD.

Speaker: Dr Manuel Schneider (National Yang Ming Chiao Tung University (NYCU))

12:30 Lunch

15 A recent global extraction of TMD distributions

After the conceptual improvements to transverse momentum dependent (TMD) extractions of a flavour dependent ansatz as well as a more robust propagation of uncertainties onto the resulting TMD functions in ART23, the following work ART25 is a state of the art determination of the unpolarised TMD parton distribution functions and -fragmentation functions such as the Collins-Soper kernel via a global fit on the available data.

With a simple model we reach a good result for the fit, overall describing the relevant phase space covered by semi-inclusive DIS and Drell-Yan experiments.

In my talk I want to review previous improvements, present our findings in this recent study, and comment on aspects on which this type of extractions can improve on.

Speaker: Dr Valentin Moos (NYCU)

16 Challenges and Strategies in Determining Longitudinal Unpolarized Proton PDFs: From the LHC to EIC Prospects

In this talk, I'll address the major challenges in determining the proton's longitudinal unpolarized parton distribution functions (PDFs), vital for Standard Model precision tests and New Physics exploration. Limitations stem from perturbative and nonperturbative QCD interactions, along with data analysis and statistical uncertainties.

Insights from LHC data inform future EIC PDF research. I'll cover theoretical frameworks, advanced statistical techniques for estimating uncertainties, and the role of lattice QCD calculations. Finally, I'll highlight how novel experimental observables can tighten PDF constraints, enhancing precision and New Physics search sensitivity.

Speaker: Prof. C.-P. Yuan (Michigan State University)