Description:

Abstract: What is really inside a proton? The fundamental building blocks of the proton, quarks and gluons, have been known for decades. However, we still have an incomplete theoretical and experimental understanding of how these particles and their dynamics give rise to the quantum bound state of the proton and its physical properties, such as for example its spin and mass. The two up and the single down quarks that comprise the proton in the simplest picture account only for a few percent of the proton mass, the bulk of which is in the form of quark kinetic and potential energy and gluon energy from the strong force. An essential feature of this force, as described by quantum chromodynamics, is its ability to create matter-antimatter quark pairs through quantum fluctuation inside the proton that exist only for a very short time. Their fleeting existence makes the antimatter quarks (also known as sea-quarks) within protons difficult to study, but their existence is discernible in reactions where a matter-antimatter quark pair annihilates.

In this picture of quark-antiquark creation by the strong force, the probability distributions as a function of momentum for the presence of up and down antimatter quarks should be nearly identical, since their masses are quite similar and small compared to the mass of the proton. However, our recent results from the Fermilab E906/SeaQuest experiment show evidence that they are very different, with more abundant down antimatter quarks than up antimatter quarks over a wide range of momentum fraction of the parent proton. These results revive interest in several proposed mechanisms as the origin of this antimatter asymmetry in the proton that had been disfavored by the previous results and point to the future measurements at the Fermilab E1039/SpinQuest that can distinguish between these mechanisms.

Seminar Speaker: Kun Liu, Los Alamos

Host: Michael Schmitt

Meeting Details:
Monday, June 7, 2021 at 4:00pm (Central Time)

Zoom info:
Please email laura.nevins@northwestern.edu to get the Zoom meeting link. 

Keywords: Physics, Astronomy, HEP