RUI: Testing Fundamental Symmetries with Muon g-2

Regis University, Denver CO

Investigators

Abstract

This award will support the PI and undergraduate students from Regis University to enable them to contribute to the Muon g-2 Experiment at Fermilab, which aims to discover new particles and interactions that are beyond the current Standard Model. The Standard Model of subatomic physics provides an overarching theoretical framework that describes all known forces except gravity. It has been extensively tested, and it successfully predicts almost every phenomenon that has ever been observed in experiments at particle accelerators. Nevertheless, it is known to be incomplete, since it does not have a way to explain dark matter or dark energy, and it does not account for the asymmetry of matter over antimatter that allowed the structures of our universe to form. Muons are in many ways similar to electrons, but with a mass approximately 207 times higher, and they are unstable, decaying in a few microseconds; they appear in nature as cosmic rays. The Muon g-2 Experiment measures the rate at which the of muons rotate as they orbit in a magnetic field. That rotation could arise from the coupling of muons to new particles. The experiment has been constructed and has completed its first year of data collection. With close mentoring from the PI and other collaborators, students will maintain and upgrade particle detectors, assist with taking data at Fermilab, and analyze data. They will have opportunities to present their work at conferences and collaboration meetings. The professional development of these students is a primary focus of this project. Entering classes at Regis University are continuing a trend of increasing ethnic and socioeconomic diversity, so the students supported by this award represent a broadening in the participation by groups that are currently underrepresented in physics research. The Muon g-2 experiment measures the muon's anomalous magnetic moment. Previous measurements of this quantity differ from theoretical predictions by about 3.5 standard deviations. The new measurement at Fermilab will record 20 times more muon decays than experiment 821 at Brookhaven National Laboratory. Systematic uncertainties will also be reduced, leading to an expected precision of 140 parts per billion. Consequently, the experiment has the potential to discover the indirect effects of new particles and interactions with very high statistical significance. The range of possible new physics is wide; it could include ideas such as supersymmetry, light weakly-interacting particles from a "dark sector," axion-like particles, or extra dimensions. Conversely, if the result turns out to agree with the Standard Model, it would provide a strong constraint on all of these new physics models. The experiment measures the rate of spin precession in flight for a muon beam in a weak-focusing 1.5 Tesla storage ring magnet. Several beam dynamics effects directly contribute to the systematic error, including coherent betatron oscillations (CBO) and muon losses, which are partly driven by the CBO. The fiber harps, which were refurbished and are maintained by the Regis group, are used to characterize and to minimize the CBO. The anticipated precision of the experiment assumes that the systematic errors from CBO and muon losses will be reduced by factors of 2.3 and 4.5, respectively. The Regis group participates in the analysis of fiber harp data in order to understand these beam dynamics effects; it also contributes to other parts of the analysis effort, including data quality control and run selection. 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.