Electric dipole moment in storage ring experiments

TL;DR

This paper revises the spin dynamics equations for electric dipole moment measurements in storage rings, accounting for nonzero pseudoscalar couplings, which could improve the accuracy of experimental tests of fundamental physics.

Contribution

It derives a corrected spin precession equation without assuming zero pseudoscalar, extending the theoretical framework for storage ring EDM experiments.

Findings

Identifies a correction term in the spin precession equation

Highlights the importance of nonzero pseudoscalar in beyond Standard Model theories

Provides a refined theoretical basis for future EDM measurements

Abstract

The measurement of electric dipole moment in storage rings can potentially exceed the sensitivity of tests with neutral systems. The spin dynamics under such conditions is described by the Bargmann-Michel-Telegdi equation. It can be derived in the semiclassical approximation under several assumptions one of which is the zero pseudoscalar bilinear. However, many promising extensions to the standard model consider scalar-pseudoscalar couplings which assume nonzero electron pseudoscalar. We re-derive the spin precession equation under conditions that do not assume that pseudoscalar is zero. It leads to a correction term that might be required for matching the storage ring measurements with QFT evaluations.