Monday November 20th, 2023 at 11am
Generalized parton distributions through universal moment parameterization: the gluonic sector with deeply virtual J/ψ production
M. Gabriel Santiago (CNF)
We present a further step toward a global extraction of gluon generalized parton distributions (GPDs). In our previous work we performed the first global analysis of quark GPDs by including lattice quantum chromodynamics (QCD) calculations, global fitted forward parton distribution functions (PDFs), form factors (FFs), and Deeply Virtual Compton Scattering (DVCS) measurements from JLab and Hadron-Electron Ring Accelerator (HERA) to constrain two quark flavors with leading order QCD evolution. There, the inclusion of DVCS did not probe gluon structure at leading order, as the gluon GPDs only enter through evolution. In this talk we discuss the inclusion of HERA measurements of Deeply Virtual Meson Production (DVMP) in order to study gluon GPDs at non-zero skewness using the same conformal moment parameterization ansatz. We concentrate our study on the production of J/ψ mesons in order to limit quark contributions and thus allow for greater constraints on the gluon GPDs at non-zero skewness.
Monday November 13th, 2023 at 11am
Measurements of Single and Pair Production of Hadrons in Nuclear SIDIS in the CLAS experiment
Sebouh Paul (Jefferson Lab)
I will present recent measurements of semi-inclusive deep-inelastic scattering measurements off nuclei with CLAS, in both single-hadron and double-hadron channels. I will describe how these measurements can constrain the interaction between quarks and cold nuclear matter, and also the nuclear modifications to transverse-momentum dependent parton-distribution functions. I will finalize by describing an upcoming eA scattering experiment with CLAS12 with a higher beam energy and much larger luminosity, as well as planned studies that will further strengthen emerging frameworks to describe these physics, including but not limited to, new Monte-Carlo generators and global QCD analyses.
Monday October 2nd, 2023 at 11am
Lattice calculation of nucleon PDFs and GPDs using Large Momentum Effective Theory
Peter Petreczky (Brookhaven National Lab)
Lattice QCD results on quark PDFs and GPDs of the nucleon obtained within the Large Momentum Effective Theory (LaMET) with NLO and NNLO matching will be presented. I will discuss how different versions of LaMET, such as the quasi-PDF approach and the short distance factorization or the pseudo-PDF approach complement each other. Results on un-polarized quark distributions and quark transversity distribution will be shown. In addition I will discuss calculations of the higher moments of unpolarized quark GPDs based on short distance factorization.
11AM - 12:30PM EDT May 22nd, 2023
Accessing GPDs using the dilepton final state: results and perspectives with CLAS12
Pierre Chatagnon (Jefferson Lab)
Generalized Parton Distributions (GPDs) describe the correlations between the longitudinal momentum and the transverse position of the partons inside the nucleon. They are nowadays the subject of an intense effort of research, in the perspective of understanding nucleon spin and the nucleon Gravitational Form Factors (GFFs). Experimentally, the main reaction to measure GPDs have been the Deeply Virtual Compton Scattering (DVCS) reaction. In this talk, I will present complementary ways to access GPDs using the dilepton final state with the CLAS12 detector. First, I will present the first measurement of the Timelike Compton Scattering reaction (the hard photoproduction of a lepton pair), that gives access to the GPDs via the beam polarization asymmetry and angular asymmetry of the electron/positron pair. This measurement was done using data taken in 2018 by the CLAS12 detector with a 10.6 GeV electron beam impinging on a liquid-hydrogen target. I will then present the current effort to extract the near-threshold J/ψ photoproduction cross section using the same dataset. This later measurement is expected to provide direct insight on the gluons GPDs of the proton.
Zoom Link: https://jlab-org.zoomgov.com/j/1601213226?pwd=dUNRdHgvMm45bDZXWWM2Y2JYenlWQT09
11AM - 12:30PM EDT May 8th, 2023
Modeling and extraction of GPDs from exclusive processes
Hervé Dutrieux (The College of William and Mary)
Generalized parton distributions (GPDs) encompass crucial information on the three-dimensional structure of hadrons and their mechanical properties via the gravitational form factors. I will discuss how their scale dependence determines the propagation of uncertainty in the deconvolution problem of hard exclusive observables, and offers at the same time a great opportunity to model GPDs in the small Bjorken-x limit. I will present a modeling strategy to implement theoretical constraints and give a more comprehensive picture of extraction uncertainties.
Zoom Link: https://jlab-org.zoomgov.com/j/1601213226?pwd=dUNRdHgvMm45bDZXWWM2Y2JYenlWQT09
11AM - 12:30PM EDT April 3rd, 2023
New methods to access GPDs from lattice QCD and synergies for nuclear tomography
Martha Constantinou (Temple University)
Traditionally, lattice QCD computations of GPDs have been carried out in a frame where the transferred momentum is symmetrically distributed between the incoming and outgoing hadrons. However, such frames are inconvenient for lattice QCD calculations since each value of the momentum transfer requires a separate calculation, increasing the computational cost. In recent work (PRD 106 (2022) 11, 114512), we lay the foundation for more effective calculations of GPDs applicable for any frame, with freedom in the transferred momentum distribution. An important aspect of the approach is the Lorentz covariant parameterization of the matrix elements in terms of Lorentz-invariant amplitudes, which allows one to relate matrix elements in different frames. We demonstrate the efficacy of the formalism through numerical calculations using one ensemble of Nf=2+1+1 twisted mass fermions with a pion mass of about 260 MeV. Concentrating on the proton and zero skewness, we extract the invariant amplitudes from matrix element calculations in both the symmetric and asymmetric frame and obtain results for the twist-2 light-cone GPDs for unpolarized quarks, H and E.
We discuss the necessity of lattice QCD calculation of GPDs in the pre-EIC era. Also, we address and complementarity to the theoretical and phenomenological communities within the scientific program of the DOE-funded QGT Topical Collaboration on the 3D quark and gluon tomography.
Zoom Link: https://jlab-org.zoomgov.com/j/1601213226?pwd=dUNRdHgvMm45bDZXWWM2Y2JYenlWQT09