Searches for Electric Dipole Moments—Overview of Status and New Experimental Efforts

Florian Kuchler

doi:10.3390/universe5020056

Abstract

Searches for permanent electric dipole moments (EDMs) of fundamental particles, atoms and molecules are promising experiments to constrain and potentially reveal beyond Standard Model (SM) physics. A non-zero EDM is a direct manifestation of time-reversal (T) violation, and, equivalently, violation of the combined operation of charge-conjugation (C) and parity inversion (P). Identifying new sources of CP violation can help to solve fundamental puzzles of the SM, e.g., the observed baryon-asymmetry in the Universe. Theoretical predictions for magnitudes of EDMs in the SM are many orders of magnitude below current experimental limits. However, many theories beyond the SM require larger EDMs. Experimental results, especially when combined in a global analysis, impose strong constraints on CP violating model parameters. Including an overview of EDM searches, I will focus on the future neutron EDM experiment at TRIUMF (Vancouver). For this effort, the TUCAN (TRIUMF Ultra Cold Advanced Neutron source) collaboration is aiming to build a strong, world leading source of ultra cold neutrons (UCN) based on a unique combination of a spallation target and a superfluid helium UCN converter. Another focus will be the search for an EDM of the diamagnetic atom 129 Xe using a 3 He comagnetometer and SQUID detection. The HeXeEDM collaboration has taken EDM data in 2017 and 2018 in the magnetically shielded room (BMSR-2) at PTB Berlin.

Highlights

The Standard Model (SM) of particle physics describes many experimental observations with impressive accuracy and successfully withstands many experimental tests
While paramagnetic atoms or molecules are sensitive to an electron electric dipole moments (EDMs) with only higher order contributions involving nuclei, diamagnetic atoms such as 199 Hg, 129 Xe or 225 Ra exhibit many CP-odd processes contributing to an EDM
With continuously supplying polarized gas diffusing from a pump cell attached to the EDM cell with high voltage electrodes, the maser technique can achieve almost continuous long-term observation

Summary

Introduction

The Standard Model (SM) of particle physics describes many experimental observations with impressive accuracy and successfully withstands many experimental tests. Three main issues to be addressed are dark energy, the nature of dark matter and the observed baryon asymmetry in our Universe. According to Sakharov [3], there are three conditions to be fulfilled for the Universe to evolve into a state of baryon asymmetry: (i) departure from thermal equilibrium; (ii) baryon number violation and (iii) C and CP violation. These conditions can in principal be accounted for within the SM, i.e., through so-called “sphaleron“ processes and electroweak symmetry breaking [4].

Methods

Results

Conclusion