RUI: Study of the Nucleon Structure Using Deeply Virtual Compton Scattering at Jefferson Lab.

Fairfield University, Fairfield CT

Investigators

Abstract

Understanding the structure of the nucleon has been the focus of many scientists for decades. Over the past 40 years there has been a tremendous theoretical and experimental advancement that brought us to the discovery of quarks as fundamental bricks of matter and the laws that govern their interactions. The generalized parton distributions (GPDs) are theoretical tools used to describe hadrons (particles that are made from quarks and gluons) in terms of their constituents. These distributions give fully correlated quark information in both coordinate and momentum space, allowing access to crucial properties such as the angular momentum distribution of quarks in the nucleon and explaining how quarks contribute to the overall properties of nucleons such as their electric and axial charge. This project will focus on experiments at Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport News, VA using the recently upgraded Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS12). Jefferson lab with its "intermediate" energies is a unique facility to explore the region sensitive to the valence quarks, and the large acceptance CLAS12 detector will allow the extraction of GPDs over large kinematic ranges. The PI of this proposal is a co-spokesperson of three experiments aimed to extraction of GPDs. The PI will take an active role in the data taking at Jefferson Lab and will contribute to the data reduction and analysis. Undergraduate students will be involved in this project and in addition to gaining experience in data analysis in particle physics, they will develop broader skills, such as coding and statistics. The cleanest way to access GPDs is via deeply virtual Compton scattering (DVCS), where the virtual photon interacts with a single quark of the nucleon radiating a real photon. At leading twist, the soft process is described by four chiral-even GPDs: the quark-helicity independent, H, E and the quark helicity dependent H-tilde and E-tilde. The focus of this project is to measure target and beam asymmetries and cross sections for the DVCS with proton and neutron targets. These observables on different nucleons have unique sensitivity to a subset of the four GPDs, and their simultaneous determination allows for a comprehensive extraction of GPDs for the proton and neutron and flavor decomposition. In September 2018, the unpolarized proton target run will start, providing a significant amount of additional production data. Experiments on the neutron target and the polarized proton target are expected to run in the next three years. Fairfield University will contribute to the physics analysis and other aspects of the data reduction such as quality tests, calibration and software development. In addition to the work on the new data, as it becomes available, Fairfield University will continue to complete simulation work in preparation to the upcoming experiments to study the optimal configuration of the detector. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.