A Program of Medium Energy Nuclear Physics

It is now a well-established fact that nucleons, protons and neutrons—particles that make up the vast majority of the visible matter in the Universe—are made up of more elementary particles called quarks. The main physics program supported by this grant is to measure how quarks are distributed in nucleons. In this quark form of matter, energy and mass are traded back and forth on short timescales according to the famous E = mc2. Particularly intriguing questions regarding this essential feature of quark matter include: What is the role of anti-matter in the nucleon? What happens when the temperature inside a nucleon is increased to a high value? The goal of these experiments is to compare with theoretical predictions from the so-called Standard Model of Particle Physics, both to better understand it, as well as to look for signs of new phenomena that are not described by it. These research efforts will contribute to the education of postdocs, graduate students, and undergraduates in a broad array of skills needed in the advanced high tech workforce. The research program also includes a number of outreach activities aimed at young students and the general public. The prevailing theory of the strong force, quantum chromodynamics or QCD, is a generalization of the highly successful QED, yet we are hard-pressed to provide truly QCD-based quantitative or intuitive descriptions of nucleons. This project will focus on investigating key properties of the proton, targeting the poorly measured sea quarks and the unknown orbital motion of the quarks and of the quark-gluon plasma (QGP) which existed at the high temperatures in the early universe before the strong force confined the quarks into bound states. This fleeting state of matter has been recreated in the laboratory and found to possess extraordinary properties, such as a viscosity so low that it may be at its theoretical minimum. This grant enables continued study of the QGP’s properties using fully reconstructed jets at ATLAS and sPHENIX. The QCD research will support work on SeaQuest at Fermilab, ATLAS at CERN, and sPHENIX at Brookhaven. The ATLAS Reaction Plane Detector is calibrated using machine learning to provide the resolution needed for the physics program. Additionally, we are investigating using machine learning to identify rapidity gaps in ultra-peripheral collisions at ATLAS. This award also supports a search for a permanent electric dipole moment (EDM) of the neutron at LANL as well as UCNtau+ and the new, complementary neutron beam lifetime experiment, BL3. 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.