Please contact Beth Demkowski, demkowsk@umich.edu for Zoom link.

Even after more than 100 years of studies, the proton is puzzling. Questions such as what is the exact size of the proton, how does the spin and the mass of the proton arise, and what is the exact composition of the proton still captivate our field. In the simplest picture, the proton is made of two up and one down quark, in a more comprehensive picture, however, the proton is a strongly-coupled, relativistic, infinite-body system, where quarks and antiquarks come in and out of existence for very short times. Their fleeting existence makes the antiquarks within protons difficult to study, but it is discernible in reactions in which a matter–antimatter quark pair annihilates. In this presentation, I will discuss a recent result published by the SpinQuest collaboration that shows that nature prefers anti-down quarks to anti-up quarks in the proton. This is in contrast to predictions from perturbative QCD where no such antiquark imbalance is expected in the proton.