Constraining interactions mediated by axion-like particles with ultracold neutrons

S Afach,V Hélaine,N Severijns,K Kirch,P Schmidt-Wellenburg,B Lauss,M Burghoff,K Bodek,M Kasprzak,A Kozela,A Mtchedlishvili,J Krempel,G Pignol,Y Kermaïdic,S Roccia,G Bison,H.-C Koch,T Lefort,P Knowles,G Ban,J Zenner,B Franke,M Fertl,J Zejma,A Schnabel,S Komposch,Y Lemière,G Zsigmond,M Daum,D Ries,D Rebreyend,A Weis,Jens‐Uwe Voigt ,O Naviliat‐Cuncic ,G Qúeḿener ,G Wyszyński ,Zoran Grujić ,P N Prashanth ,F M Piegsa

doi:10.1016/j.physletb.2015.04.024

Abstract

We report a new limit on a possible short range spin-dependent interaction from the precise measurement of the ratio of Larmor precession frequencies of stored ultracold neutrons and Hg199 atoms confined in the same volume. The measurement was performed in a ∼1μT vertical magnetic holding field with the apparatus searching for a permanent electric dipole moment of the neutron at the Paul Scherrer Institute. A possible coupling between freely precessing polarized neutron spins and unpolarized nucleons of the wall material can be investigated by searching for a tiny change of the precession frequencies of neutron and mercury spins. Such a frequency change can be interpreted as a consequence of a short range spin-dependent interaction that could possibly be mediated by axions or axion-like particles. The interaction strength is proportional to the CP violating product of scalar and pseudoscalar coupling constants gSgP. Our result confirms limits from complementary experiments with spin-polarized nuclei in a model-independent way. Limits from other neutron experiments are improved by up to two orders of magnitude in the interaction range of 10−6<λ<10−4m.

Highlights

We present an interpretation of our recent measurement of the ratio γn/γHg of the neutron and 199Hg magnetic moments [1] in terms of the strength of a possible short range spin-dependent neutron–nucleon interaction
Afach et al / Physics Letters B 745 (2015) 58–63 measurement was performed using the apparatus dedicated to the search for the neutron electric dipole moment [2] by the nEDM Collaboration at the source for ultracold neutrons [3] of the Paul Scherrer Institute, Switzerland
Due to the non-observation of the nEDM a short range spin-dependent interaction mediated by an axion is constrained to gS g P < 10−40 . . . 10−34 [16]

Summary

Introduction

We present an interpretation of our recent measurement of the ratio γn/γHg of the neutron and 199Hg magnetic moments [1] in terms of the strength of a possible short range spin-dependent neutron–nucleon interaction. This ratio was inferred from a comparison of the simultaneously recorded Larmor precession frequencies of the two species contained in the same storage volume. Possible force mediators are axions, or axion-like particles and the interaction strength is proportional to the product of scalar and pseudoscalar coupling constants gS g P It has been proposed in [5,6] to use an nEDM apparatus for the investigation of such a force.

Motivation

The measurement with the nEDM apparatus

Derivation of the pseudomagnetic field

Details on the measurement of the ratio R and the center-of-mass offset h

Findings

Result and comparison to other experiments