Novel Insights on the Proton Structure from J/ψ Measurements at Jefferson Lab

Protons and neutrons, collectively called nucleons, are the main building blocks of all the visible matter in the universe and nearly all the mass of the visible universe is within the mass of these nucleons. Thus, understanding the internal structure of the nucleons is essential to our understanding of the fundamental building blocks of visible matter in the universe. While the theory of Quantum Chromo Dynamics (QCD) successfully describes the interactions between the quarks and gluons, constituents of the nucleons, understanding how the quarks and gluons give rise to the mass, spin, and other intrinsic properties of the nucleons still remains as one of the greatest challenges. Recent studies suggested that J/ψ photo-production near threshold provides a unique window into the gluonic structure of the proton, enabling access to information regard- ing the origin of its mass which is dominated by the energy carried by gluons. The recent discovery of the charm pentaquarks by the LHCb Collaboration at CERN happens to be in this near threshold region of J/ψ as well, spurring a new excitement and a sense of urgency to carry out J/ψ photo-production measurements.

In this talk, I will present an overview of the J/ψ measurements at Jefferson Lab with an emphasis on the J/ψ − 007 experiment, that was conducted in the experimental Hall C. I will discuss this experiment’s findings on the LHCb’s charm pentaquarks as well as the insights we gained on the proton structure, particularly the proton mass. I will follow this with a brief summary of the future opportunities pertain to this research at the existing and future facilities, Jefferson Lab and Electron Ion Collider, respectively.