Session 3WQB: 3D Hadron Structure from Next-Generation Scattering Experiment and Lattice QCD II

Single diffractive hard exclusive processes for the study of generalized parton distributions

Generalized parton distributions (GPDs) are important non-perturbative functions that provide tomographic images of the partonic structures of hadrons. We introduce a type of exclusive processes for a better study of GPDs, which we refer to as single diffractive hard exclusive processes (SDHEPs), and give a general proof for their factorization into GPDs. We demonstrate that the SDHEP is not only sufficiently generic to cover all known processes but also well motivated for searching for new processes for extracting GPDs. Importantly, we also examine the sensitivity of the SDHEP to the parton momentum fraction $x$ dependence of GPDs, and demonstrate quantitatively with two processes that can be readily measured at J-PARC/AMBER and JLab, respectively.   

SoLID Double Deeply Virtual Scattering in Hall A Jefferson Laboratory

The SoLID spectrometer being developped in Hall A at Jefferson Laboratory is a solenoidal spectrometer designed to be able to run at high luminosity up to 10^38 cm-2.s-1.

Such luminosity allows to measure low cross section processes such as Double Deeply Virtual Compton Scattering experiment, which would allow to map Generalized Parton Distribution at different skewness compared to existing data from Deeply Virtual Compton Scattering.

I will present the proposal for a DDVCS experiment in parallel of the J/Psi SoLID experiment and possible future dedicated experiments at 11 and 22 GeV.   

DVCS and HEMP at COMPASS experiment for GPD studies

COMPASS is a fixed target experiment with a high energy muon beam from the SPS at CERN. One of the important aims of the experiment is to study  the 3D structure of the nucleon

from the point of view of Generalized Parton Distributions(GPD).  In the experiment, Deeply Virtual Compaton Scattering(DVCS) and Hard  Exclusive Meson Production(HEMP) processes have been studied intensively. Following the COMPASS setup ,  the experimental results obtained so far on the DVCS and the HEMP will be presented.  The results include the cross section of the DVCS and the exclusive neutral pion production and the transverse target spin asymmetries and  spin density matrix elements for the exclusive  production of rho and omega  mesons.  Based on the results on the t-slope of the DVCS,  we discuss about the transverse extenstion of partons in nucleon.  The results for the HEMP,  constraints for the GPD models are given.   

Recent progress on nucleon form factors in lattice QCD at the physical point

We present results for the isovector axial charge and root-mean-square (RMS) radii of the nucleon obtained from 2+1 flavor lattice QCD at the physical point with a large spatial extent of about 10 fm. Our calculations are performed with the PACS10 gauge configurations generated by the PACS Collaboration with the six stout-smeared O(a) improved Wilson-clover quark action and Iwasaki gauge action at beta=1.82 and 2.00 corresponding to lattice spacings of 0.085 fm and 0.063 fm respectively. We first evaluate the axial charge, which is one of the most important pieces of information on the nucleon structure. Moreover, we also calculate the nucleon elastic form factors and determine three kinds of isovector RMS radii such as electric, magnetic and axial ones at the two lattice spacings. We finally discuss the discretization uncertainties on the axial charge and isovector RMS radii towards the continuum limit.   

Accessing x-dependent GPDs from lattice QCD

Generalized parton distributions (GPDs) are important quantities that characterize the 3-D structure of hadrons, and complement the information extracted from TMDs. They provide information about the partons' momentum distribution and also on their distribution in position space. Most of the information from lattice QCD is on the Mellin moments of GPDs, namely form factors and their generalizations. Recent developments in calculations of matrix elements of boosted hadrons coupled with non-local operators opened a new direction for extracting the x dependence of GPDs.