Physics (Internal)

Searching for Physics Beyond the Standard Model Through Dipole Interactions

This event is part of the Physics Department Colloquia Series.

Abstract: I will review physics of the electric and magnetic dipole operators, first focusing on the history, which is intimately tied to the development of the standard model, and then on the searches for physics beyond the Standard Model using the dipole interaction. The measurement of magnetic dipoles of elementary particles began with the experiments of Stern and Gerlach, which eventually told us that the g‐factor for spin was 2. Refined investigations showed that g_s > 2, which resulted in the first “quantum loop” calculation by Schwinger. The magnetic anomalies, a=(g‐2)/2 of the electron and muon are now known to a relative precisions of ±0.23 parts per billion and ±0.54 parts per million respectively, and there appears to be a several sigma difference between the measured muon anomaly and the Standard‐Model value. The related electric dipole moment (EDM), which is forbidden by parity and time reversal symmetries (and by implication the combination of charge conjugation‐parity), has been searched for down to sensitivities of ~10^-26 e‐cm and ~10^‐19 e‐cm, with no hint of a signal. Since the Standard‐Model EDM is < 10^‐36 e‐cm, the experimental observation of an EDM would signify the presence of new physics, and a new, non‐Standard‐Model source of CP violation, which is needed to explain the predominance of matter over anti‐matter in the universe. Observation of the related Standard‐Model forbidden process μ+ → e+ γ, or the spontaneous conversion of a muon to an electron in the field of an atomic nucleus, which could also go through a dipole operator, would unambiguously signify the presence of New Physics: Charged lepton flavor violation.