Conveners
3D Structure of the Nucleon: GPDs and Form Factors: GPDs I
- Dave Gaskell (Jefferson Lab)
3D Structure of the Nucleon: GPDs and Form Factors: GPDs II
- Lubomir Pentchev (Jefferson Lab)
3D Structure of the Nucleon: GPDs and Form Factors: GPD III
- Kyungseon Joo (University of Connecticut)
3D Structure of the Nucleon: GPDs and Form Factors: GPDs IV
- Paweł Sznajder (National Centre for Nuclear Research)
3D Structure of the Nucleon: GPDs and Form Factors: GPDs V
- Yoshitaka Hatta (Brookhaven National Laboratory)
Perturbative evolution offers the well-identified possibility of reconstructing the skewness dependence of generalized parton distributions (GPDs) in the small Bjorken x domain. This general idea has notably been used to constrain gluon PDFs at small x from exclusive heavy meson photoproduction. We study the regime of validity and the uncertainty associated to this method. We discuss more...
The feasibility of extracting generalized parton distributions (GPDs) from deeply-virtual Compton scattering (DVCS) data has recently been questioned because of the existence of an infinite set of so-called ``shadow GPDs'' (SGPDs). These SGPDs depend on the process and manifest as multiple solutions (at a fixed scale $Q^2$) to the inverse problem that needs to be solved to infer GPDs from DVCS...
The Fourier transforms of generalized parton distributions (GPDs) give single-particle spatial densities of the quarks and gluons inside the proton. The physical properties derived from GPDs include the average radius of each partonic component of the nucleon and other quantities. To capture a fuller dynamical picture of the proton’s internal structure, information on the relative position...
I will discuss the recent progress of the generalized parton distributions (GPDs) through universal moment parameterization (GUMP) program for the global analysis of GPDs that aims to combine the experimental inputs as well as lattice simulation results for a better determination of GPDs. I will briefly report the current status of the program and also discuss the important future developments.
Deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP) are well known to provide access to the generalised parton distributions (GPDs) of the nucleon. The COMPASS collaboration at CERN studied them in 2012, 2016 and 2017 using a 160 GeV $\mu^+$ and $\mu^-$ beam and a liquid hydrogen target. The beam was longitudinally polarised in opposite directions depending on...
The Gravitational Form Factors (GFFs) give access to the internal distributions of mass, pressure and shear force inside the proton. They were considered experimentally unmeasurable for decades due to the very weak gravitational interaction. The Generalized Parton Distributions (GPDs), which describe the correlations between the longitudinal momentum and the transverse position of the partons...
Electron scattering experiments sensitive to meson structure are made challenging by the lack of free meson targets. Experiments at Jefferson Lab make use of the nucleon's intrinsic meson cloud to study both the elastic and inelastic structure of pions and kaons. In experimental Hall C a program of exclusive pion electroproduction measurements (E12-19-006) will measure the t-dependence of the...
In this talk, I will discuss the exclusive photoproduction of a photon-meson pair with large $p_T$ as a channel to probe GPDs. Like other $2 \to 3$ exclusive processes, this channel allows us to better study the $x$-dependence of GPDs, unlike other $2 \to 2$ processes such as DVCS which give "moment-type" information. Moreover, it also gives the possibility to access chiral-odd GPDs at the...
In this talk we present our results for the exclusive photoproduction of the $D$-meson pairs with large invariant mass. We perform evaluations in the collinear factorization framework and in the leading order of the strong coupling $\alpha_s$, expressing the cross-section in terms of generalized parton distributions (GPDs) of different parton flavors in the proton. We focus on the...
Generalized parton distributions describe the non-forward matrix elements of QCD light-ray operators between hadronic states and unify the concepts of parton densities and hadron form factors. The concept can be extended to transitions between states with different hadronic composition, including multi-hadron states and resonances. These "transition GPDs" offer new opportunities for exploring...
One of the major challenges of modern theoretical and experimental hadron physics is to probe the Q^2 evolution of the transition form factors of a nucleon to its excited states in terms of the underlying fundamental degrees of freedom, namely, quarks and gluons. The pattern of their mass generation is firmly encoded in the non-perturbative solutions of the fundamental equations of motions of...
The recent exclusive backward-angle electroproduction of mesons from Jefferson Lab electron-proton fixed-target scattering experiments hints on a new domain of applicability of QCD factorization in a unique u-channel kinematics regime. The interests of studying nucleon structure through u-channel meson production observables have grown significantly.
In the fixed target configuration, the...
We present a theoretical update on the analysis of threshold heavy quarkonium e.g., $J/\psi$, production measurements. It has been shown that the such processes can be factorized with gluon generalized parton distributions (GPDs) which allow us to further connect to the gluonic gravitational form factors (GFFs) in the large $\xi$ limit. We will discuss the GPDs at large skewness with more...
Starting from the Weinberg formalism for the construction of fields for arbitrary spin, we propose an algorithm for the construction of the independent operators that enter the scattering amplitude associated with electromagnetic observables. This procedure is advantageous for the systematic study of the structure of hadrons and nuclei, particularly in the case of spin-dependent observables....
Nucleon elastic form factors encode crucial information about its charge and magnetization distributions. For many decades, nucleon form factors were studied by using unpolarized electron-nucleon cross section measurements. The advent of electron beams with higher luminosities and beam polarization coupled with large acceptance detectors, polarized targets and recoil polarimeters enabled a...
Measurements of the elastic electromagnetic form factors of the proton and neutron have been a central component of Jefferson Lab’s scientific program for almost four decades and have been important, among other things, in constraining Generalized Parton Distributions and testing the validity of the onset of perturbative quantum chromodynamics. The ratio of $G_E^p/G_M^p$ measured in the late...
The elastic form factors of the proton and neutron are fundamental observables representing a projection of the internal structure of the nucleon. Measurements of the electromagnetic form factors of the proton and neutron can be combined to separately determine contributions from the $u$ and $d$ constituents of the nucleon, however, this interpretation relies on assumptions of both charge...
We present the first calculation of twist-3 axial quark GPDs of the proton using lattice QCD combined with the large momentum effective theory (LaMET) approach. We use one ensemble of twisted mass fermions with degenerate light quarks, a strange and a charm quark, at a single lattice spacing of 0.093 fm and a pion mass of 260 MeV. We employ three proton boosts up to 1.67 GeV to test the...
We present a lattice QCD determination of Mellin moments of unpolarized generalized parton distributions (GPDs) of the proton from an analysis of the quasi-GPD matrix elements within the short-distance factorization framework. We perform our calculation on an $N_f$=2+1+1 twisted mass fermions ensemble with a clover improvement at lattice spacing $a=0.093$ fm and a pion mass of $m_\pi=260$ MeV....
We present a Lattice QCD calculation of the generalized parton distributions (GPDs) for the pion. Focusing on the zero skewness, we obtain the matrix elements from both symmetric and asymmetric kinematic frames with the recently proposed Lorentz-invariant definition. The calculations are performed using a single ensemble of $N_f=2+1$ highly-improved staggered quarks with $m_\pi = 300$ MeV and...
Testing detailed predictions of QCD and searching for phenomena at the LHC requires knowing spin dependent Parton Distribution Functions for quarks and gluons. For some observables Generalized or Transverse Momentum pdf’s are needed. Calculating these distributions from QCD, ab initio, is prohibitively resource intensive and depends on non-perturbative techniques. Quantum simulation on a...
Hard Exclusive Meson Production (HEMP) and Deeply Virtual Compton Scattering (DVCS) are very promising reactions to access Generalized Parton Distributions (GPDs). Such exclusive measurements were performed at COMPASS in 2016 and 2017 at the M2 beamline of the CERN SPS using the 160 GeV muon beam scattering off a 2.5 m long liquid hydrogen target surrounded by a barrel-shaped time-of-flight...
