CAREER:Nucleon Structure, Fundamental Symmetries, and Lattice QCD

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

Protons and neutrons are the basic building blocks of all visible matter. They were created in the Big Bang together with antiprotons and antineutrons. It is unknown why more particles than antiparticles have been created in the early Universe, and it is the particles that have survived to become all of the presently existing nuclear matter. Such an imbalance may occur only if physical laws are not exactly symmetric when time is reversed. If this is the case, nuclear experiments must observe precession (rotation) of neutrons in an electric field. In the next decade the precision of such experiments will be improved 100-fold. This project is aimed at providing the theoretical foundations to examine whether experiments agree with known interactions of elementary particles or not, and measure how much the space reflection and time reversal symmetries of physical laws are broken. These questions are at the heart of modern nuclear physics and they have to be answered to understand the origin of all known matter. Electric dipole moments (EDMs) of nucleons (protons and neutrons), nuclei, and atoms can be induced by time reversal (T) symmetry-violating interactions of elementary particles that comprise them. While the standard model contains T violation, the violation is not sufficiently large to produce the observed baryon asymmetry of the Universe. This alone points to new, yet unknown types of particle interactions, such as color-electric dipole moments of quarks, three-gluon, and four-quark effective interactions. EDMs of nucleons and nuclei may also be produced by nontrivial topology of gauge fields (the so-called theta-term) that has not been observed so far. While the theory governing quarks and gluons is known, it is intractable analytically, and requires numerical calculations (lattice QCD) to compute nucleon structure and EDMs, which is the aim of this project. Current and future experiments measuring EDMs are thus at the frontier of fundamental physics. Their interpretation, however, depends critically on precise theoretical calculations of nucleon structure that will be performed in this project. 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.