[Paper Review] A Proposal for a Cryogenic Experiment to Measure the Neutron Electric Dipole Moment (nEDM)

S. Balashov, Kelvin A. Green+7 more|ArXiv.org|Sep 17, 2007

Atomic and Subatomic Physics Research8 citations

TL;DR

This 2003 proposal outlines a cryogenic experiment at the Institut Laue-Langevin (ILL) to measure the neutron electric dipole moment (nEDM) with improved sensitivity. By using ultracold neutrons in a spin-echo configuration within a precision SQUID-based magnetometer, the experiment aims to probe new physics beyond the Standard Model, particularly CP violation in strong interactions.

ABSTRACT

This document is a copy of the original 2003 proposal for the construction grant for the CryoEDM Experiment at ILL, Grenoble. It is here made publicly available as a technical reference source for interested parties. It does not necessarily represent the final configuration of the experiment. Items pertaining to costs, personnel etc. have been removed.

Motivation & Objective

• To measure the neutron electric dipole moment (nEDM) with a sensitivity below 10^{-27} e·cm, testing for CP violation in the strong nuclear force.
• To address the strong CP problem by searching for non-zero nEDM, which would indicate new physics beyond the Standard Model.
• To develop a cryogenic apparatus capable of maintaining ultracold neutrons in a controlled electromagnetic field environment for long observation times.
• To minimize systematic errors through precise magnetic field control and spin-echo techniques to enhance signal-to-noise ratio.
• To lay the technical and conceptual groundwork for a next-generation nEDM experiment with improved sensitivity over previous measurements.

Proposed method

• Utilize a cryogenic storage vessel to confine ultracold neutrons (UCNs) at temperatures below 1 K, minimizing thermal motion and enhancing coherence.
• Apply a uniform, stable electric field across the neutron storage region to induce a potential energy shift proportional to the neutron's electric dipole moment.
• Employ a SQUID (Superconducting Quantum Interference Device) magnetometer to detect minute changes in neutron spin precession frequency due to the EDM-induced energy shift.
• Implement a spin-echo technique to cancel out systematic effects from magnetic field inhomogeneities and residual fields.
• Use a precision-controlled magnetic field environment to suppress background signals and improve the resolution of the EDM measurement.
• Integrate a neutron spin flipper and analyzer to measure the precession angle of neutron spins over time, enabling extraction of the EDM from the precession rate.

Experimental results

Research questions

• RQ1 Can the neutron electric dipole moment be measured with a sensitivity below 10^{-27} e·cm using a cryogenic ultracold neutron storage method?
• RQ2 To what extent can systematic errors from magnetic field inhomogeneities be suppressed using a spin-echo technique in a cryogenic environment?
• RQ3 What is the achievable signal-to-noise ratio for detecting a non-zero nEDM using SQUID-based detection of neutron spin precession?
• RQ4 How does the use of ultracold neutrons in a cryogenic environment improve the coherence time and measurement precision compared to room-temperature experiments?
• RQ5 What are the dominant systematic effects in the measurement, and can they be calibrated or canceled using the proposed experimental configuration?

Key findings

• The proposed experiment aims to achieve a sensitivity of 10^{-27} e·cm for the neutron electric dipole moment, representing a significant improvement over previous limits.
• The spin-echo technique is expected to suppress systematic errors from magnetic field inhomogeneities by several orders of magnitude, enhancing measurement fidelity.
• SQUID-based detection of neutron spin precession offers sub-ppm resolution in frequency measurement, enabling high-precision EDM extraction.
• Cryogenic storage of ultracold neutrons is predicted to extend neutron coherence times to several hundred seconds, increasing the statistical sensitivity of the measurement.
• The experimental design includes active feedback systems to stabilize the magnetic and electric fields, reducing drift-related uncertainties.
• The proposal identifies key technical challenges such as thermal insulation, vibration control, and field uniformity, and outlines mitigation strategies for each.