The search for the neutron electric dipole moment at PSI

Guillaume Pignol,Philipp Schmidt-Wellenburg

doi:10.21468/scipostphysproc.5.027

Guillaume Pignol, Philipp Schmidt-Wellenburg

Open Access

https://doi.org/10.21468/scipostphysproc.5.027

Copy DOI

Abstract

The existence of a nonzero permanent electric dipole moment (EDM) of the neutron would reveal a new source of CP violation and shed light on the origin of the matter–antimatter asymmetry of the Universe. The sensitivity of current experiments using stored ultracold neutrons (UCN) probe new physics beyond the TeV scale. Using the UCN source at the Paul Scherrer Institut, the nEDM collaboration has performed the most sensitive measurement of the neutron EDM to date, still compatible with zero (|d_n|<1.8\times 10^{-26} \, e {cm}|dn|<1.8×10−26ecm, C.L.,90%). A new experiment designed to improve the sensitivity by an order of magnitude, n2EDM, is currently under construction.

Highlights

The permanent electric dipole moment (EDM) d of a simple quantum system of spin 1/2 represents the coupling between the particle spin and an externally applied electric field E, in the same way that the magnetic dipole moment μ quantifies the coupling between the spin and an applied magnetic field B
Because σ · E is odd with respect to time reversal, the CPT theorem implies that a non-zero EDM would result in a violation of CP symmetry
The generation of experiments with improved sensitivity are motivated by the exciting possibility of discovering a non-zero EDM induced by new physics at the multi-TeV scale

Summary

27.1 Introduction

The permanent electric dipole moment (EDM) d of a simple quantum system of spin 1/2 represents the coupling between the particle spin and an externally applied electric field E, in the same way that the magnetic dipole moment μ quantifies the coupling between the spin and an applied magnetic field B. After a phase of hardware upgrades and commissioning of the instrument, data was collected during 2015 and 2016 This resulted in the currently most precise measurement of the neutron EDM, dn = (0.0 ± 1.1stat ± 0.2sys) × 10−26 e · cm [12]. The construction of the new double chamber instrument (called n2EDM: the new neutron EDM apparatus) started in 2018. We elaborate on the main challenges to neutron EDM searches

27.2 The three challenges for searches for the neutron EDM

27.3 Measurement and result

27.5 Outlook and world-wide competition