RUI: Testing Fundamental Symmetries with Muon Experiments

Regis University, Denver CO

Investigators

Abstract

This award will support the Regis University group in continuing to probe one of the few known experimental discrepancies with the Standard Model of subatomic physics, which encodes our understanding of the fundamental building blocks of matter and energy. The Fermilab Muon g-2 experiment observes muons, which are subatomic particles that are like massive electrons, as they move through a magnetic field. It measures the rate at which the muons’ spin directions rotate; this rate is determined by the sum of the muons’ interactions of all kinds, potentially including interactions with new particles or via new kinds of forces that have not yet been discovered directly. The Standard Model makes a precise theoretical prediction; it differs from the recently-published result from the experiment’s first year of data collection at a level that may reveal the effects of new physical processes. A much larger data set has already been collected and is being analyzed, and one additional year of data collection is expected. Meanwhile, the precision of the Standard Model prediction is limited primarily by the uncertainty of the contributions to it from hadrons: particles that are composed of quarks and gluons, which are the domain of nuclear physics. The Regis group will participate substantially both in the completion of the Fermilab experiment and in the development of the MUonE experiment at CERN, which will measure the hadronic contributions with an independent method. Regis University’s physics program is undergraduate-focused, and this award will generate opportunities for physics majors and minors to become involved in leading-edge research in nuclear physics. They will develop laboratory, data analysis, and computing skills as they participate, with substantial mentoring, in the Muon g-2 and MUonE experiments. Furthermore, Regis University is a diverse campus, so many of the students who will be supported by this renewed grant are expected to be from groups that are currently underrepresented in the sciences. The Muon g-2 experiment will improve the precision of the measurement of the muon’s anomalous magnetic moment from 350 to 140 parts per billion (ppb), providing a window for discovery. Extending the experiment to the negative muon polarity in the final run, as is planned, will also allow for a precision test of CPT and Lorentz symmetries. The uncertainty associated with the Standard Model prediction, which is currently 370 ppb, will soon be the limiting factor in interpreting the Muon g-2 result. This uncertainty arises predominantly from the hadronic vacuum polarization component, which MUonE will determine from the running of the electromagnetic coupling (alpha) with energy scale in elastic scattering of a muon beam from target electrons. The Regis University group will continue to operate and analyze data from the “fiber harp” beam monitoring detectors in the Muon g-2 experiment, and to further develop the collaboration’s Monte Carlo simulations, which will be used to study questions related to the dynamic motion of the stored muon beam. The Regis group will also contribute to the completion of the technical proposal for the MUonE experiment and to its first physics data collection, initially taking on roles in the design, simulation, and testing of the electromagnetic calorimeter and other downstream detector components. 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.