Abstract: The proton, a key building block of all visible matter, boasts intrinsic properties such as electric charge, mass, and spin. These features are born from the intricate dynamics of its fundamental constituents - quarks and gluons. While the electric charge and spin of protons have been extensively studied via electron scattering, leading to substantial knowledge of the proton’s electric charge radius, our comprehension of its mass structure, predominantly governed by the energy of the gluons, is still limited. This colloquium will explore the process of studying the proton’s mass structure with photoproduction and electron scattering experiments, drawing parallels with the measurement techniques of the neutron skin in lead-208. We will discuss our most recent findings on the proton’s mass radius, achieved through near-threshold J/ψ photoproduction at Jefferson Lab. Lastly, we will outline future experiments at Jefferson Lab and the Electron-Ion Collider aimed at further elucidating the mass structure of nucleons and nuclei.

Refreshments will be served before the Colloquium in the Auditorium Lounge