A search for neutron to mirror-neutron oscillations using the nEDM apparatus at PSI

C Abel ,I Rienäcker ,S Emmenegger ,S Roccia ,O Naviliat‐Cuncic ,B Lauss ,M Rawlik ,N Severijns ,G Bison ,M Daum ,N J Ayres ,Prajwal Mohanmurthy ,Zoran Grujić ,K Kirch ,P Koss ,D Ries ,F M Piegsa ,Nora Hild ,H.-C Koch ,R Tavakoli Dinani ,E Wursten ,Christopher Crawford ,T Lefort ,В М Бондар ,D Rebreyend ,G Pignol ,D Rozpȩdzik ,P Schmidt-Wellenburg ,A Kozela ,William C Griffith ,Jacob Thorne ,E Chanel ,K Bodek ,G Ban ,J Zejma ,J Krempel ,L Ferraris-Bouchez ,D Pais ,A Leredde ,A Weis ,P.-J Chiu ,P Flaux ,G Zsigmond

doi:10.1016/j.physletb.2020.135993

Abstract

It has been proposed that there could be a mirror copy of the standard model particles, restoring the parity symmetry in the weak interaction on the global level. Oscillations between a neutral standard model particle, such as the neutron, and its mirror counterpart could potentially answer various standing issues in physics today. Astrophysical studies and terrestrial experiments led by ultracold neutron storage measurements have investigated neutron to mirror-neutron oscillations and imposed constraints on the theoretical parameters. Recently, further analysis of these ultracold neutron storage experiments has yielded statistically significant anomalous signals that may be interpreted as neutron to mirror-neutron oscillations, assuming nonzero mirror magnetic fields. The neutron electric dipole moment collaboration performed a dedicated search at the Paul Scherrer Institute and found no evidence of neutron to mirror-neutron oscillations. Thereby, the following new lower limits on the oscillation time were obtained: τnn′>352 s at B′=0 (95% C.L.), τnn′>6s for 0.4μT<B′<25.7μT (95% C.L.), and τnn′/cos⁡β>9s for 5.0μT<B′<25.4μT (95% C.L.), where β is the fixed angle between the applied magnetic field and the local mirror magnetic field, which is assumed to be bound to the Earth. These new constraints are the best measured so far around B′∼10μT and B′∼20μT.

Highlights

Lee and Yang noted, in their landmark paper [1], that parity symmetry in the weak interaction could be restored with the introduction of a parity conjugated copy of the same weakly interacting particles
Foot and Volkas [3,4] detailed the aforementioned idea that by the introduction of mirror matter, parity and time reversal symmetries could be restored in the electroweak interactions, and in a global sense as well
Several works considered that mixing of SM and SM particles could provide answers to a number of outstanding issues in physics today

Summary

Introduction

Lee and Yang noted, in their landmark paper [1], that parity symmetry in the weak interaction could be restored with the introduction of a parity conjugated copy of the same weakly interacting particles. Where μn = −60.3 neV/T is the magnetic moment of the neutron, nn = hτn−n1 is the mass mixing term yielding a characteristic time for the n − n oscillation, τnn , and B( ) is the (mirror) magnetic field vector. Berezhiani [27] pointed out that in order to set constraints on τnn as a function of the mirror magnetic field it is convenient to work with the observables ‘ratio’ (E B ) and ‘asymmetry’ ( A B ), respectively, defined as: E (ts B. where the n{(t0s,)B,−B} are the number of neutrons counted after storage for time ts. When we assume the mirror magnetic field to be zero (B = 0), the relationships between the n − n oscillation time, τn(nB =0), and the ratio observable in Eq (5) becomes independent of the applied magnetic field.

Experiment setup and data collection

Data analysis and results

Calculation of the free flight time distributions

Constraints on the ratio and asymmetry observables

Findings

Discussion