Our celebration of Dr. Kyle Steffen's successful doctoral dissertation defense, with his supervisor, Dr. Mike Snow.
Dissertation Title: Probing Fundamental Symmetry Violations with Neutron Polarimetry
Abstract: Neutrons, as massive neutral fermions that can be produced in high intensities, are ideal for precision experiments probing magnetic, strong, weak, and gravitational interactions. Using low-energy beams of spin-polarized neutrons, which can be manipulated by optical techniques and magnetic fields, standard and exotic spin-dependent interactions can be probed through changes induced in the neutron polarization. This work examines two experimental tests of fundamental symmetry violations using neutron polarimetry.
First, the development of the third-generation Neutron Spin Rotation (NSR) collaboration polarimeter is detailed along with a novel liquid helium target system and cryogenic reciprocating bellows pump which aims to improve the measurement of parity-violating neutron optical rotary power in liquid helium by an order of magnitude to the sensitivity of <E-7 rad/m. This improved precision is expected to provide the first non-zero measurement of parity-violation in this nuclear system, offering crucial input into the hadronic weak interaction description of low-energy QCD. The experience gained from this experiment is also utilized to aid in the design of a novel proton detector system for the third-generation neutron beam lifetime (BL3) experiment.
Second, the violation of Lorentz symmetry is investigated within the framework of the Standard Model Extension (SME). This theory predicts that the spontaneous breaking of local Lorentz symmetry leads to sidereal time-dependent couplings between spin-polarized fermions and the gravitational field in earthbound laboratories. Using angle-encoded neutron spin echo techniques on the Offspec instrument at the ISIS neutron source, neutron states are produced with spin components which sample different heights of the local gravitational field. By searching for time-varying signals in the measured spin polarization of these neutron states, constraints are placed on the magnitude of Lorentz-violating SME couplings between fermions and gravity.
