Year of Publication
Doctor of Philosophy (PhD)
Arts and Sciences
Physics and Astronomy
Dr. Susan Gardner
In the Standard Model (SM), the quantity baryon number (B) − lepton number (L), B − L, is perfectly conserved. Therefore, the observation of B − L violation would reveal the existence of physics beyond the SM. Traditionally, given the severe experimental constraints on |∆B| = 1 processes, B − L violation with baryons is probed via neutron-antineutron (n − n̄) oscillations, although this process suffers from quenching in the presence of external fields or matter.
In this dissertation, we discuss another possibility, n − n̄ conversion, in which the |∆B| = 2 process appears with an external source. We start with the Lorentz invariant B − L violating operators of lowest mass dimension and show how the appearance of constraints on the “arbitrary” phases in the discrete symmetry trans- formations help restrict the possible low energy n − n̄ transformation operators. To explain the appearance of CPT odd n − n̄ transition operators (although they eventually vanish due to the fermion anticommutation relations), we connect it to theories of self-conjugate isofermions and show that the appearance of n − n̄ oscillations cannot occur in pure Quantum Chromodynamics (QCD) in the chiral limit. We then show how n − n̄ conversion can be free from quenching and demonstrate one way how it can be connected to n − n̄ oscillations since the quarks carry electromagnetic charge. Effective field theory is utilized to find the quark-level conversion operators and to determine the coupling parameter associated with the nuclear-level conversion operators. Finally, we argue how n − n̄ conversion can provide a complementary probe to oscillation experiments. We discuss possible n − n̄ conversion proposals and explicitly show how n − n̄ conversion experiments can set limits on the scale of B − L violation.
Digital Object Identifier (DOI)
Yan, Xinshuai, "NEUTRON-ANTINEUTRON TRANSITIONS: EXPLORING B – L VIOLATION WITH QUARKS" (2017). Theses and Dissertations--Physics and Astronomy. 46.