We present for the first time a detailed and comprehensive analysis of the experimental results that set the current world sensitivity limit on the magnitude of the electric dipole moment (EDM) of the neutron. We have extended and enhanced our earlier analysis to include recent developments in the understanding of the effects of gravity in depolarizing ultracold neutrons; an improved calculation of the spectrum of the neutrons; and conservative estimates of other possible systematic errors, which are also shown to be consistent with more recent measurements undertaken with the apparatus. We obtain a net result of dn=−0.21±1.82×10−26  e cm, which may be interpreted as a slightly revised upper limit on the magnitude of the EDM of 3.0×10−26  e cm (90% C.L.) or 3.6×10−26  e cm (95% C.L.).

/pdf/revised-experimental-upper-limit-on-the-electric-dipole-19hu918ip2.pdf

Revised experimental upper limit on the electric dipole moment of the neutron

We present the result of an experiment to measure the electric dipole moment EDM) of the neutron at the Paul Scherrer Institute using Ramsey's method of separated oscillating magnetic fields with ultracold neutrons (UCN). Our measurement stands in the long history of EDM experiments probing physics violating time reversal invariance. The salient features of this experiment
were the use of a Hg-199 co-magnetometer and an array of optically pumped cesium vapor magnetometers to cancel and correct for magnetic field changes. The statistical analysis was performed on blinded datasets by two separate groups while the estimation of systematic effects profited from an
unprecedented knowledge of the magnetic field. The measured value of the neutron EDM is $d_{\rm n} = (0.0\pm1.1_{\rm stat}\pm0.2_{\rmsys})\times10^{-26}e\,{\rm cm}$.

/pdf/measurement-of-the-permanent-electric-dipole-moment-of-the-8jsk17vj92.pdf

Measurement of the Permanent Electric Dipole Moment of the Neutron.

The Surrounding Field Compensation (SFC) system described in this work is installed around the four-layer Mu-metal magnetic shield of the neutron electric dipole moment spectrometer located at the Paul Scherrer Institute. The SFC system reduces the DC component of the external magnetic field by a factor of about 20. Within a control volume of approximately 2.5 m × 2.5 m × 3 m, disturbances of the magnetic field are attenuated by factors of 5–50 at a bandwidth from 10−3 Hz up to 0.5 Hz, which corresponds to integration times longer than several hundreds of seconds and represent the important timescale for the neutron electric dipole moment measurement. These shielding factors apply to random environmental noise from arbitrary sources. This is achieved via a proportional-integral feedback stabilization system that includes a regularized pseudoinverse matrix of proportionality factors which correlates magnetic field changes at all sensor positions to current changes in the SFC coils.

/pdf/dynamic-stabilization-of-the-magnetic-field-surrounding-the-1xvxrv8ffb.pdf

Dynamic stabilization of the magnetic field surrounding the neutron electric dipole moment spectrometer at the Paul Scherrer Institute

We present the new spectrometer for the neutron electric dipole moment (nEDM) search at the Paul Scherrer Institute (PSI), called n2EDM. The setup is at room temperature in vacuum using ultracold neutrons. n2EDM features a large UCN double storage chamber design with neutron transport adapted to the PSI UCN source. The design builds on experience gained from the previous apparatus operated at PSI until 2017. An order of magnitude increase in sensitivity is calculated for the new baseline setup based on scalable results from the previous apparatus, and the UCN source performance achieved in 2016.

/pdf/the-n2edm-experiment-at-the-paul-scherrer-institute-3dh0o2t3el.pdf

The n2EDM experiment at the Paul Scherrer Institute

This paper summarizes the results from measurements aiming to characterize ultracold neutron detection with 6Li-doped glass scintillators. Single GS10 or GS20 scintillators, with a thickness of 100-200μm, fulfill the ultracold neutron detection requirements with an acceptable neutron-gamma discrimination. This discrimination is clearly improved with a stack of two scintillators: a 6Li-depleted glass bonded to a 6Li-enriched glass. The technique of optical contact bonding is used between the two glasses in order to eliminate the need for optical glue or grease between them. Relative to a 3He Strelkov gas detector, the scintillator’s detection efficiency is lower for UCN energies close to the scintillator’s Fermi potential (85-100 neV), but becomes larger at higher UCN energies. Coupled to a digital data acquisition system, counting rates up to a few 105 counts/s can be handled. A detector based on such a scintillator stack arrangement was built and has been used in the neutron electric dipole moment experiment at the Paul Scherrer Institute since 2010. Its response for routine runs of the neutron electric dipole moment experiment is presented.

Ultracold neutron detection with 6Li-doped glass scintillators - NANOSC: A fast ultracold neutron detector for the nEDM experiment at the Paul Scherrer Institute

A description is presented of apparatus used to carry out an experimental search for an electric dipole moment of the neutron, at the Institut Laue-Langevin (ILL), Grenoble. The experiment incorporated a cohabiting atomic-mercury magnetometer in order to reduce spurious signals from magnetic field fluctuations. The result has been published in an earlier letter [1]; here, the methods and equipment used are discussed in detail.

/pdf/apparatus-for-measurement-of-the-electric-dipole-moment-of-2xmo3w6ko5.pdf

Apparatus for measurement of the electric dipole moment of the neutron using a cohabiting atomic-mercury magnetometer

The reflection losses for stored ultracold neutrons have been calculated for various profiles of molecular number density at the wall surface. The results show relatively low sensitivity to realistic departures from a simple step function. For a surface density rising as a linear ramp extending over a depth of 100 A, in the case where the mean Fermi potentials is 100 neV, the losses are only about 4% higher than those for the abrupt step case. The same degree of insensitivity has been found for other shapes of profile. The effect on the losses of a reduced Debye temperature in the first few atomic layers of the surface is also considered.

Surface density profiles and the rate of loss of stored ultracold neutrons

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Apparatus for measurement of the electric dipole moment of the neutron using a cohabiting atomic-mercury magnetometer

Surface density profiles and the rate of loss of stored ultracold neutrons