The neutron electric dipole moment experiment at the Spallation Neutron Source

¹ North Carolina State University, Raleigh, NC 27695, USA
² Triangle Universities Nuclear Laboratory, Durham, NC 27708, USA
³ Duke University, Durham, NC 27708, USA
⁴ North Carolina Central University, Durham, NC 27707, USA
⁵ Arizona State University, Tempe, AZ 85287, USA
⁶ University of Kentucky, Lexington, KY 40506, USA
⁷ University of Virginia, Charlottesville, VA 22904, USA
⁸ Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
⁹ Universidad Nacional Autonóma de Mexico, Apartado Postal 20-364, México
¹⁰ Bartoszek Engineering, Aurora, IL 60506, USA
¹¹ University of Illinois Urbana-Champaign, Champaign, IL 61801, USA
¹² Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹³ California Institute of Technology, Pasadena, CA 91125, USA
¹⁴ Los Alamos National Laboratory, Los Alamos, NM 87545, USA
¹⁵ Mississippi State University, Mississippi State, MS 39762, USA
¹⁶ University of Tennessee, Knoxville, TN 37996, USA
¹⁷ Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
¹⁸ Tennessee Technological Institute, Cookeville, TN 38501, USA
¹⁹ Yale University, New Haven, CT 06520, USA
²⁰ Indiana University, Bloomington, IN 47408, USA
²¹ Brown University, Providence, RI 02912, USA
²² Harvard University, Cambridge, MA 02138, USA
²³ Valparaiso University, Valparaiso, IN 46383, USA

^a e-mail: kkleung@ncsu.edu
^b e-mail: Present address: IBS Center for Axion and Precision Physics Research.

Published online: 12 December 2019

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 ³He, and superfluid ⁴He will be exploited to provide a sensitivity to ∼ 10⁻²⁸ e · cm. Our cryogenic apparatus will deploy two small (3 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 ³He 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.