Measurement Of Neutron Electric Dipole Moment Research Articles

Approaches to high-density storage experiments with in-situ production and detection of ultracold neutrons

Low counting statistics is one of the most important challenges in modern experiments with ultracold neutrons (UCN). UCN densities in superthermal sources based on superfluid helium are normally much higher than those after UCN delivery to ex-situ volumes. Therefore, and due to the vanishing neutron absorption of 4He, storage-based experiments performed in-situ promise significant sensitivity gains. Scalable measurements offer a promising path to simultaneously address the inefficient use of cold neutron beams as precursors for UCN production in 4He, by recuperating the unused beam fraction, and confront the practical challenges of large-scale UCN infrastructure. We suggest strategies for the development of modular cryogenic cells, propose a novel approach for in-situ UCN detection, and discuss the ultimate statistical reach of such a multiplexed experiment for measuring the neutron’s permanent electric dipole moment (EDM). While dedicated research and development are needed to evaluate the feasibility for many requirements, a neutron EDM measurement with sensitivity well beyond 10 − 28 e cm seems possible. Such an experiment could be pursued at any compatible cold neutron beamline, e.g., at the Institut Laue–Langevin, or later using the ANNI facility or large beam port (LBP) at the European Spallation Source.

Precision measurement and suppression of low-frequency noise in a current source with double-resonance alignment magnetometers

Low-noise high-stability current sources have essential applications such as neutron electric dipole moment measurement and high-stability magnetometers. Previous studies mainly focused on frequency noise above 0.1 Hz while less on the low-frequency noise/drift. We use double resonance alignment magnetometers (DRAMs) to measure and suppress the low-frequency noise of a homemade current source (CS) board. The CS board noise level is suppressed by about 10 times in the range of 0.001–0.1 Hz and is reduced to at 0.001 Hz. The relative stability of CS board can reach 2.2 × 10–8. In addition, the DRAM shows a better resolution and accuracy than a commercial 7.5-digit multimeter when measuring our homemade CS board. Further, by combining the DRAM with a double resonance orientation magnetometer, we may realize a low-noise CS in the 0.001–1000 Hz range.

Mapping of the magnetic field to correct systematic effects in a neutron electric dipole moment experiment

Experiments dedicated to the measurement of the electric dipole moment of the neutron require outstanding control of the magnetic field uniformity. The neutron electric dipole moment (nEDM) experiment at the Paul Scherrer Institute uses a 199Hg co-magnetometer to precisely monitor magnetic field variations. This co-magnetometer, in the presence of field non-uniformity, is responsible for the largest systematic effect of this measurement. To evaluate and correct that effect, offline measurements of the field non-uniformity were performed during mapping campaigns in 2013, 2014 and 2017. We present the results of these campaigns, and the improvement the correction of this effect brings to the neutron electric dipole moment measurement.

High-resolution two-photon spectroscopy of a 5p56p←5p6 transition of xenon

We report high-resolution Doppler-free two-photon excitation spectroscopy of Xe from the ground state to the $5{p}^{5}(^{2}P_{3/2})6p\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}^{2}[3/2]_{2}$ electronic excited state. This is a first step to developing a comagnetometer using polarized $^{129}\mathrm{Xe}$ atoms for planned neutron electric dipole moment measurements at TRIUMF. Narrow linewidth radiation at 252.5 nm produced by a continuous wave laser was built up in an optical cavity to excite the two-photon transition, and the near-infrared emission from the $5{p}^{5}6p$ excited state to the $5{p}^{5}6s$ intermediate electronic state was used to detect the two-photon transition. Hyperfine constants and isotope shift parameters were evaluated and compared with previously reported values. In addition, the detected photon count rate was estimated from the observed intensities.

Lepton electric dipole moment and strong CP violation

Contribution of the strong CP angle, θ¯, to the Wilson Coefficients of electron and muon electric dipole moment (EDM) operators are discussed. Previously, θ¯ contribution to the electron EDM operator was calculated by Choi and Hong [1]. However, the effect of CP-violating three meson coupling was missing in [1]. We include this missing contribution for the first time in the literature, and reevaluate the Wilson coefficients of the lepton EDM operator. We obtain de=−(2.2–8.6)×10−28θ¯e-cm which is 15–70% of the result obtained in [1]. We also estimated the muon EDM as dμ=−(0.5–1.8)×10−25θ¯e-cm. Using |θ¯|≲10−10 suggested by the neutron EDM measurements, we obtain |de|≲8.6×10−38e-cm and |dμ|≲1.8×10−35e-cm. The θ¯ contribution to the muon EDM is much below the sensitivities of the current and near future experiments. Our result shows that the θ¯ contribution to de,μ can be larger than the CKM contributions by many orders of magnitude.

EDM: Neutron electric dipole moment measurement

An electric dipole moment (EDM) of the neutron would be a clear sign of new physics beyond the standard model of particle physics. The search for this phenomenon is considered one of the most important experiments in fundamental physics and could provide key information on the excess of matter versus antimatter in the universe. With high measurement precision, this experiment aims to ultimately achieve a sensitivity of 10-28 ecm, a 100-fold improvement in the sensitivity compared to the state-of-the-art. The EDM instrument is operated by an international collaboration based at the Technische Universität München.

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

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.

Neutron electric dipole moment measurement with a buffer gas comagnetometer

A neutron EDM measurement with a comagnetometer is discussed. For magnetometry, polarized xenon atoms are injected into a cylindrical cell where a cylindrically symmetric magnetic field and an electric field are applied for the EDM measurement. The geometric phase effect (GPE), which originates from particle motion in a magnetic field gradient, is analyzed in terms of the Dyson series. The motion of the xenon atom is largely suppressed because of a small mean free path. The field gradient is controlled by means of NMR measurements, where the false effect of Earthʼs rotation is removed. As a result, the GPE is reduced below 10−28e cm.

Neutron electric dipole moment measurements at the ILL

The origin of the CP violation which created the matter in the universe is one of the enduring mysteries of fundamental physics. Particle electric dipole moments provide a sensitive probe of CP violation from new physics. The article describes past and future work being done at the ILL in Grenoble to search for an electric dipole moment of the neutron.

Dressed spin ofHe3

We report a measurement of dressed spin effects of polarized $^{3}\mathrm{He}$ atoms from a cold atomic source traversing a region of a constant magnetic field ${B}_{0}$ and a transverse oscillatory dressing field ${B}_{d}\mathrm{cos}{\ensuremath{\omega}}_{d}t$. The observed effects are compared with a numerical simulation using the Bloch equation as well as a calculation based on the dressed atom formalism. An application of the dressed spin of $^{3}\mathrm{He}$ for a proposed neutron electric dipole moment measurement is also discussed.

Nuclear electric dipole moment with relativistic effects in Xe and Hg atoms

The atomic electric dipole moment (EDM) is evaluated by considering the relativistic effects as well as nuclear finite size effects in Xe and Hg atomic systems. Due to Schiff's theorem, the first order perturbation energy of EDM is canceled out by the second order perturbation energy for the point nucleus. The nuclear finite size effects arising from the intermediate atomic excitations may be finite for deformed nucleus but it is extremely small. The finite size contribution of the intermediate nuclear excitations in the second order perturbation energy is completely canceled by the third order perturbation energy. As the results, the finite contribution to the atomic EDM comes from the first order perturbation energy of relativistic effects, and it amounts to around 0.3 and 0.4 percents of the neutron EDM ${d}_{n}$ for Xe and Hg, respectively, though the calculations are carried out with a simplified single-particle nuclear model. From this relation in Hg atomic system, we can extract the neutron EDM which is found to be just comparable with the direct neutron EDM measurement.

Solid deuterium and UCN factory: application to the neutron electric dipole moment measurement

Present experiments which search for an electric dipole moment (EDM) of the neutron use ultra-cold neutrons (UCN) and are limited by counting statistics. One way to solve this problem is to improve the source of UCN. The present article briefly reviews two possibilities which employ solid deuterium at the temperature of liquid helium. The possibility of installing a solid deuterium UCN source at the FRM-II reactor and at spallation neutron sources at PSI, LANL and KEK is discussed. An increase of the UCN density up to the level of 10 3–10 4 cm −3 is expected. Compared to existing sources, this corresponds to an improvement by two to three orders of magnitude. Such experimental facilities will make it possible to improve measurements of the EDM of the neutron down to the level of 10 −27 e cm.

Test of Time Reversal Invariance using Neutrons

Measurements of neutron electric dipole moment (EDM) have provided the most strict and reliable upper limit on T-violating interactions. It is well known that neutron EDM is sensitive to theoretical models which explain the CP-violation in K-meson. Another approach to T-violation using neutrons is the measurement of T-odd term in p-wave neutron capture reactions in the incident energy region of about eV. In the compound states formed by the p-wave neutron capture reactions, an enhancement of T-violating interaction is theoretically predicted based on the interference of two opposite parity amplitudes. A brief review of neutron EDM measurements and an overview of T-violation experiment in eV-neutron capture reactions are given.

Test of time reversal invariance using neutrons

Measurements of neutron electric dipole moment (EDM) have provided the most strict and reliable upper limit on T-violating interactions. It is well known that neutron EDM is sensitive to theoretical models which explain the CP-violation in K-meson. Another approach to T-violation using neutrons is the measurement of T-odd term in p-wave neutron capture reactions in the incident energy region of about eV. In the compound states formed by the p-wave neutron capture reactions, an enhancement of T-violating interaction is theoretically predicted based on the interference of two opposite parity amplitudes. A brief review of neutron EDM measurements and an overview of T-violation experiment in eV-neutron capture reactions are given.

Neutron magnetic resonance experiments

Abstract Neutron magnetic resonance experiments are reviewed from the first experiments of Alvarez and Bloch on the neutron magnetic moment published in 1940 to the most recent neutron electric dipole moment measurements with bottled neutrons. The first measurements on the neutron magnetic moment were accurate to 1 part per 100 whereas the latest neutron beam magnetic resonance experiment at the ILL in Grenoble gives μn = 1.04066884(26) × 10-3μB where μB is the Bohr magne ton, a result good to 0.25 parts per million. Early neutron beam magnetic resonance experiments setting a low upper limit tot he neutron electric dipole moment are also described. The latest and most sensitive electric dipole measurements are with neutrons stored for up to 80 s in a beryllium oxide cylindrical bottle with Be lids. With such an apparatus a value of (0.3±4.8) × 10-25e cm has been measured at Grenoble and with a somewhat different apparatus at Leningrad a value of (2.3±2.3) × 10-25e cm has been found. Plans for even more sensitive measurements are described. Finally, experiments are described for measuring parity non-conserving rotations of the neutron spin on passage through Sn, Pb and La.

Experimental tests for some quantum effects in gravitation

The existing impressive tests for general relativity are shown not to yield very useful information on the possible quantum gravitational interactions. The possibility is raised here that intrinsic spins may behave differently from orbital angular momenta in external gravitational fields. The dominant spin interactions are most generally characterized by three parameters α 1, α 2, α 3. All the metric theories of gravitation predict α 1 = α 2 = 0. Indirect limits posed on these parameters by existing data are not very meaningful ( α i ≲ 10 10). Feasible experiments based on the neutron electric dipole moment measurement techniques are discussed and shown to offer the possibility of measuring α 1 ∼ 1. Other possible experimental set ups are also briefly reviewed. The existence of these effects is shown to imply the breakdown of the equivalence principle. In particular, α 1 ≠ 0, α 2 ≠ 0 also implies the breakdown of discrete symmetries in gravitation ( C, P, T). Theoretical frameworks that accommodate such effects are analyzed. A reinterpretation of Einstein's generalized gravitational theory as well as a recent theoretical proposal of Hayashi are shown to be sufficiently general for this purpose. Other important implications of these quantum effects are discussed in detail.