My research is in fundamental symmetries at the precision and intensity frontier. These experiments can have sensitivities to new physics that are comparable to high energy experiments such as those at the largest colliders. My specific area of expertise is precision measurement and control of magnetic fields, which are essential experimental components in a wide range of experiments, and especially in EDM (electric dipole moment) searches, where the external magnetic field is often the source of limiting uncertainties, both statistically (by limiting measurement times due to loss of spin coherence) and systematically (mainly due to false-EDM signals). My research focuses on designing and measuring magnetic fields, and their application to measuring fundamental symmetries, especially through EDMs.
Muon g-2 and computation methods
The Muon g-2 experiment at Fermilab is probing the magnetic moment anomaly of the muon. The previous experiment, done at Brookhaven National Laboratory, found tantalizing hints that the Standard Model prediction of the muon’s magnetic moment was inconsistent with the experiment value. The new experiment at Fermilab was started with the goal of reducing the uncertainty on the experimental value. Along with a concerted effort by the g-2 Theory Initiative to reduce the theoretical uncertainty, the goal is to determine whether or not there are signs of new physics in the discrepancy. We published our results from Run-1 in April 20211, which upheld the previous disagreement between theory and experiment, and are working towards publication of our Run-2 and Run-3 datasets. We expect to begin taking data for Run-6 in October 2022, which will be our final data taking period.
My graduate work and some of my postdoctoral work has been focused on analyzing the magnetic field data for Muon g-2. This year marks the beginning of our final data run, but analysis will continue for several years more. Most recently, I have been using PINNs (Physics-Informed Neural Networks)2 to generate a model of the magnetic field in the Muon g-2 storage ring. A PINN can fit data while respecting the underlying physical laws, such as Maxwell’s equations. This project is of particular interest to me because, while it shows a lot of promise, it also has many obstacles to overcome. For example, sometimes we do not have enough data to fully solve Maxwell’s equations (in Muon g-2, this is because we have scalar magnetometers that measure the field magnitude, but not direction), which prevents the PINN from converging to a single solution. Instead, we can get a class of solutions, which can then be analyzed for common features and differences.
Moving forward with my work on Muon g-2, I would like to develop more techniques for using PINNs to solve complex field-mapping problems. This primarily involves developing techniques to get as much information as possible out of data sets, even when convergence is not guaranteed. I want to begin this work using the Muon g-2 dataset because it is already very well analyzed using standard methods, meaning that new methods can be compared to the earlier results. Going forward, however, the same techniques can be used to analyze other magnetic fields, such as those in the nEDM experiments at both LANL (Los Alamos National Laboratory) and Oakridge National Laboratory. Developing methods for analyzing magnetic field data using PINNs is also a promising graduate and undergraduate research opportunity. The resource requirements for this computational project are minimal, although there is a great possibility for overlap between hardware development and analysis techniques for other projects that will be described later.
Neutron EDM experiments
My current research on fundamental symmetries focuses on searches for excess CP-violation by searching for permanent EDMs. The observed asymmetry between matter and antimatter in the universe is widely considered to be one of the great puzzles in physics, and, in 1967, Andrei Sakharov proposed three conditions that must be satisfied in order to generate a matter-dominated universe3. One of these three conditions is that there must exist C and CP symmetry violating processes. The Standard Model admits small amounts of CP violation, but not nearly enough to explain the matter-antimatter asymmetry. Permanent, intrinsic EDMs are violations of CP symmetry, so, by searching for larger-than-expected EDMs, we are effectively searching for the processes that led to the abundance of matter in the universe. One system where we can search for an EDM is in neutrons. I am currently involved in two neutron EDM experiments, one based at LANL that is expected to begin taking data within a year, and another based at Oakridge’s Spallation Neutron Source that is still under development.
I look forward to continued involvement in the LANL nEDM experiment. This experiment is slated to begin data taking later this year, with an expected five years of running time to reach its sensitivity goals. My contributions are focused on measuring the magnetic field and performing systematic studies. Currently, we are characterizing the primary holding B0 field and building the B1 coils that will apply a pi/2 pulse to the neutrons and mercury comagnetometers. Field characterization will remain an important activity going forward, especially considering the lessons learned by the nEDM experiment at PSI4. The development, maintenance, and analysis of an offline field mapper will help to control key systematic effects that will limit our ultimate sensitivity. This timeline presents ideal research projects for students who are early in their graduate studies, as well as opportunities for advanced undergraduates to get involved with both experimental design and analysis. There is also significant overlap between development of a magnetic field mapper and work on field analysis techniques mentioned above.
Beyond continued involvement at LANL, I also plan to contribute to the nEDM experiment at the Spallation Neutron Source at Oakridge (nEDM@SNS). The experiment is not expected to turn on until after the LANL nEDM experiment has completed, so the expertise we develop during the LANL experiment will be able to transfer to nEDM@SNS. This project is also larger, presenting opportunities for more students to get involved on a longer timeline. Our contributions would be similar as those to LANL nEDM, but because nEDM@SNS is still under development, there are also opportunities in the next few years to expand our involvement and scope of high-quality projects for students.
Summary
These three experiments are in different stages of their lifetimes, so there are opportunities for immediate projects for students, as well as the ability to ramp up over the course of several years. There is a great deal of overlap between the three experiments, so work done on each can naturally apply to the others, allowing my group to develop expertise and generational memory. Additionally, these projects represent a prompt transition from startup funds to external funding. Finally, the work done on these three external experiments will directly complement my research program at FRIB.
References
1. Abi, B. et al. Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm. Physical Review Letters 126, 141801 (2021).
2. Raissi, M., Perdikaris, P. & Karniadakis, G. E. Physics-informed neural networks: A deep learning framework for solving forward and inverse problems involving nonlinear partial differential equations. Journal of Computational Physics 378, 686–707 (2019).
3. Sakharov, A. D. Violation of CP Invariance, C asymmetry, and baryon asymmetry of the universe. Pisma Zh. Eksp. Teor. Fiz. 5, 32–35 (1967).
4. Abel, C. et al. Mapping of the magnetic field to correct systematic effects in a neutron electric dipole moment experiment. Phys. Rev. A 106, 032808 (2022).
Last edited 28 November 2022.