RUI: Fundamental Symmetry Experiments with Muons

Regis University, Denver CO

Investigators

Abstract

The study of fundamental symmetries in the field of nuclear physics explores the nature of the matter, energy, and forces that define the universe and that have allowed stars, planets, and life to emerge and flourish. This award will support the PI and undergraduate students to work on two experiments that will further our understanding of that universe. The first experiment, called MuSun, addresses one of the most important limitations of calculations related to the proton-proton fusion process that releases most of the energy in stars like the Sun. It will provide data that will calibrate the least precise parts of these calculations and can also be applied to other important nuclear reactions. The second, known as the Muon g-2 experiment, tests our Standard Model of particles and their interactions. While this model has been remarkably successful, it is not complete. The previous generation of this experiment uncovered a strong hint of a discrepancy between its measurement and the Standard Model's prediction; the new experiment will probe it with enough precision to potentially claim a discovery. Students will have opportunities to carry out guided research related to the larger physics goals, to work at major research facilities, and to attend conferences and collaboration meetings. This grant will provide opportunities to involve and support a talented and diverse group of science students that includes women, members of underrepresented ethnic groups, and first-generation college students. MuSun measures the rate of muon capture in deuterium, a fundamental two-nucleon process that provides a calibration of effective field theories of weak interactions in light nuclei. The muon capture process studied by the MuSun experiment is analogous to reactions that include proton-proton fusion and the deuteron breakup reactions that were used to detect neutrinos at the Sudbury Neutrino Observatory. The MuSun result will dramatically improve the precision of the low-energy constants describing two-nucleon terms in chiral effective field theories that describe these reactions. The Muon g-2 experiment at Fermilab will be the group's primary focus for this grant period. This experiment measures the anomalous magnetic moment of the muon by observing the rate of spin precession of a muon beam as it circulates in a precisely shimmed storage ring magnet. The spin polarization precesses because of coupling to virtual particles, including all of the particles described by the Standard Model and potentially any new, as-yet-undiscovered particles and interactions that are beyond it. The Regis group will be responsible for the implementation, installation, commissioning, and analysis for the fiber harp beam monitors and entrance counters for this experiment. The measurement clearly has the potential to discover new physics beyond the Standard Model. When the existing precision of 0.5 parts per million from the Brookhaven National Laboratory experiment is compared with modern Standard Model calculations, there is a discrepancy of more than three standard deviations; the probability of a fluctuation at this level by chance is less than one in a thousand. As the precision of the experiment reaches its 0.14 part-per-million goal, the discrepancy could exceed the discovery threshold of five standard deviations. Such a finding could represent the discovery of supersymmetry, new gauge bosons such as dark photons, or other new particles or interactions.