# The neutron electric dipole moment experiment at the Spallation Neutron Source

## TL;DR

The paper describes the design and expected sensitivity of the nEDM@SNS experiment, which aims to measure the neutron electric dipole moment with unprecedented precision using innovative cryogenic techniques and systematic error controls.

## Contribution

It introduces a novel experimental setup combining polarized ultracold neutrons, $^3$He, and superfluid helium to achieve higher sensitivity and systematic error mitigation in neutron EDM measurements.

## Key findings

- Design of a cryogenic apparatus with two small measurement cells
- Enhanced electric field strength and precession time compared to previous methods
- Implementation of two measurement modes for result validation

## Abstract

Novel experimental techniques are required to make the next big leap in neutron electric dipole moment experimental sensitivity, both in terms of statistics and systematic error control. The nEDM experiment at the Spallation Neutron Source (nEDM@SNS) will implement the scheme of Golub & Lamoreaux [Phys. Rep., 237, 1 (1994)]. The unique properties of combining polarized ultracold neutrons, polarized $^3$He, and superfluid $^4$He will be exploited to provide a sensitivity to $\sim 10^{-28}\,e{\rm \,\cdot\, cm}$. Our cryogenic apparatus will deploy two small ($3\,{\rm L}$) measurement cells with a high density of ultracold neutrons produced and spin analyzed in situ. The electric field strength, precession time, magnetic shielding, and detected UCN number will all be enhanced compared to previous room temperature Ramsey measurements. Our $^3$He co-magnetometer offers unique control of systematic effects, in particular the Bloch-Siegert induced false EDM. Furthermore, there will be two distinct measurement modes: free precession and dressed spin. This will provide an important self-check of our results. Following five years of "critical component demonstration," our collaboration transitioned to a "large scale integration" phase in 2018. An overview of our measurement techniques, experimental design, and brief updates are described in these proceedings.