Spin Sum Rules and Polarizabilities

The Gerasimov-Drell-Hearn sum rule and related dispersive integrals connect real and virtual Compton scattering to inclusive photo- and electroproduction. Being based on universal principles as causality, unitarity, and gauge invariance, these relations provide a unique testing ground to study the internal degrees of freedom that hold a system together. The present contribution reviews the spin-dependent sum rules and cross sections of the nucleon. At small momentum transfer, the data sample information on the long range phenomena (Goldstone bosons and collective resonances), whereas the primary degrees of freedom (quarks and gluons) become visible at large momentum transfer (short distance). The rich body of new data covers a wide range of phenomena from coherent to incoherent processes, and from the generalized spin polarizabilities on the low-energy side to higher twist effects in deep inelastic scattering.Comment: 15 pages, 7 figures, Proc. of Spin structure at long distance, Newport News, Virginia, 200

GPDs and DVCS with Positrons

The beam charge asymmetry helps to isolate the real part of the deeply virtual Compton scattering (DVCS) amplitude. It is discussed what information can be gained both from the real and imaginary part of the DVCS amplitude.Comment: 5 pages, 2 figures, invited talk at `Workshop on Positrons at Jefferson Lab

New measurement of charge asymmetry xF3x{F}_3 from HERA

After presenting the recent measurements of neutral current cross section in DIS at HERA, we explain the effect of the $\gamma-Z_0$ interference at the electro-weak scale, visible on these data. Then, the beam charge difference $x{F}_3$ is measured and the interference itself is extracted. Results are discussed in the context of perturbative QCD.Comment: 4 pages, 3 figures, proceedings of the International Workshop on Positrons at Jefferson Lab (March 25-27, 2009), Thomas Jefferson National Accelerator Facility, Newport News, V

Two-photon exchange measurements with positrons and electrons

Two-photon exchange contributions have potentially broad ranging impact on several charged lepton scattering measurements. Previously believed to be extremely small, based in part on comparisons of positron scattering and electron scattering in the 1950s and 1960s, recent data suggest that the corrections may be larger than expected, in particular in kinematic regions that were inaccessible in these early positron scattering measurements. Additional measurements using positron beams at Jefferson Lab would allow for a detailed investigation of these contributions in a range of reactions and observables.Comment: 6 pages, proceedings from the International Workshop on Positrons at Jefferson Lab (JPOS09), Jefferson Lab, Newport News, VA, March 25-27, 200

VAIM for Solving Inverse Problems

In this work, we propose the Variational Autoencoder Inverse Mapper (VAIM) to solve inverse problems, where there is a demand to accurately restore hidden parameters from indirect observations. VAIM is an autoencoder-based neural network architecture. The encoder and decoder networks approximate the forward and backward mapping, respectively, and a variational latent layer is incorporated into VAIM to learn the posterior parameter distributions with respect to the given observables. VAIM shows promising results on several artificial inverse problems. VAIM further demonstrates preliminary effectiveness in constructing the inverse function mapping quantum correlation functions to observables in a quantum chromodynamics analysis of nucleon structure and hadronization.https://digitalcommons.odu.edu/gradposters2021_sciences/1005/thumbnail.jp

Extraction of the neutron F2 structure function from inclusive proton and deuteron deep-inelastic scattering data

The available world deep-inelastic scattering data on proton and deuteron structure functions F2p, F2d, and their ratios, are leveraged to extract the free neutron F2n structure function, the F2n/F2p ratio, and associated uncertainties using the latest nuclear effect calculations in the deuteron.Special attention is devoted to the normalization of the proton and deuteron experimental datasets and to the treatment of correlated systematic errors, as well as the quantification of procedural and theoretical uncertainties. The extracted F2n dataset is utilized to evaluate the Q2 dependence of the Gottfried sum rule and the nonsinglet F2p - F2n moments. To facilitate replication of our study, as well as for general applications, a comprehensive DIS database including all recent JLab 6 GeV measurements, the extracted F2n, a modified CTEQ-JLab global PDF fit named CJ15nlo_mod, and grids with calculated proton, neutron and deuteron DIS structure functions at next-to-leading order, are discussed and made publicly available.Comment: 52 pages, 16 figures.https://www.jlab.org/theory/cj, https://github.com/JeffersonLab/CJ-databas

Quark-Hadron Duality for the Pion: a Phenomenological Study

We explore the relationship between exclusive and inclusive electromagnetic scattering from the pion, focusing on the transition region at intermediate Q{sup 2}. Combining Drell-Yan data on the leading twist quark distribution in the pion with a model for the resonance region at large x, we calculate QCD moments of the pion structure function over a range of Q{sup 2}, and quantify the role of higher twist corrections. Using a parameterization of the pion elastic form factor and phenomenological models for the pi --> p transition form factor, we test the extent to which local duality may be valid for the pion