In the realm of particle physics, researchers are continually pushing the boundaries of our understanding. Among them are W. C. Haxton and Evan Rule, affiliated with the University of Washington and the University of California, respectively. Their recent work delves into the intriguing phenomenon of muon-to-electron conversion, a process that could potentially reveal new physics beyond the Standard Model.
Muons are unstable subatomic particles that typically decay into electrons and neutrinos. However, certain theories predict that muons could also convert directly into electrons without emitting neutrinos. This rare process, known as charged lepton flavor violation (CLFV), is forbidden in the Standard Model but is predicted by some theories that extend it. If observed, it could provide a window into new physics.
Haxton and Rule have developed an effective theory to describe muon-to-electron conversion. Their approach involves a systematic expansion in velocities and momenta, which allows them to factor the conversion rates into two parts: particle physics terms and nuclear physics terms. The particle physics terms are expressed as bilinears in the low-energy constants (LECs) of the effective theory, while the nuclear physics terms are the associated nuclear responses.
The researchers liken the nuclear responses to “dials” that can be adjusted by selecting targets with specific properties. For instance, in the case of the Mu2e and COMET experiments, an important dial is the inelastic transitions to certain low-energy nuclear states that are resolvable in aluminum-27 (27Al). By exploiting these transitions, the experiments could not only discover CLFV but also determine the operators responsible for it.
Moreover, Haxton and Rule discuss how results from low-energy experiments can be “ported” to higher energies through a tower of matched effective field theories (EFTs). This would allow them to combine the results with other experimental limits to further constrain CLFV.
The practical applications for the energy sector are not immediately apparent, as this research is primarily focused on fundamental particle physics. However, a deeper understanding of the fundamental forces and particles that make up our universe could potentially lead to new technologies and energy sources in the future. For now, the work of Haxton and Rule represents a significant step forward in our quest to understand the fundamental nature of the universe.
This research was published in the journal Physical Review D.
This article is based on research available at arXiv.