Electric dipole moment searches: reexamination of frequency shifts for particles in traps

In experiments searching for a nonzero electric dipole moment of trapped particles, frequency shifts correlated with an applied electric field can be interpreted as a false signal. One such effect, referred to as the geometric phase effect, is known to occur in a magnetic field that is nonperfectly homogeneous. The increase in sensitivity of experiments demands improved theoretical description of this effect. In the case of fast particles, like atoms at room temperature and low pressure, the validity of established theories was limited to a cylindrical confinement cell in a uniform gradient with cylindrical symmetry. We develop a more general theory valid for an arbitrary shape of the magnetic field as well as for arbitrary geometry of the confinement cell. Our improved theory is especially relevant for experiments measuring the neutron electric dipole moment with an atomic comagnetometer. In this context, we have reproduced and extended earlier numerical studies of the geometric phase effect induced by localized magnetic impurities

Probing fundamental symmetries with ultra-cold neutrons: the measurement of the neutron electric dipole moment at PSI

Experiments searching for a permanent electric dipole moment of the neutron (nEDM) aim at discovering new sources of CP violation beyond the Standard Model of particle physics and understanding the origin of the matter-antimatter asymmetry of the Universe. So far, no evidence for such an intrinsic property was observed, neither for the neutron nor for any other system. The quest for the neutron electric dipole moment (neutron EDM) started more than sixty years ago. In recent experiments, polarized ultra-cold neutrons are stored in material bottles, subject to a strong electric field and a weak uniform magnetic field. I will discuss some of the most recent developments and their impact on both the sensitivity and the control of the systematic effects. I will give you an outlook on the key aspects of such a high accuracy experiment. I will present the latest measurement to date*, more than a decade after the former one, established by a collaboration of 15 institutions at the Paul Scherrer Institute in Switzerland. This measurement provides the best limit on the neutron EDM and demonstrates how systematic effects can be overcome, paving the way for a new generation of experiments. * C. Abel et al., Phys. Rev. Lett. 124, 081803 (2020)</p

B(E2) anomalies in the yrast band of 170Os

Background: The neutron-deficient osmium isotopic chain provides a great laboratory for the study of shape evolution, with the transition from the soft triaxial rotor in 168Os to the well-deformed prolate rotor in 180Os, while shape coexistence appears around N = 96 in 172Os. Therefore, the study of the Os isotopic chain should provide a better understanding of shape changes in nuclei and a detailed scrutiny of nuclear structure calculations. In this paper, the lifetimes of the low-lying yrast states of 170Os have been measured for the first time to investigate the shape evolution with neutron number. Purpose: Lifetimes of excited states in the ground-state band of 170Os are measured to investigate the shape evolution with neutron number in osmium isotopes and compare with state-of-the-art calculations. Methods: The states of interest were populated via the fusion-evaporation reaction 142Nd(32S, 4n) at a bombarding energy of 170 MeV at the ALTO facility from IPN (Orsay, France). Lifetimes of the 2+ 1 and 4+ 1 states in 170Os were measured with the recoil-distance Doppler-shift method using the Orsay universal plunger system. Results: Lifetimes of the two first excited states in 170Os were measured for the first time. A very small B(E2; 4+ 1 → 2+ 1 )/B(E2; 2+ 1 → 0+ 1 ) = 0.38(11) was found, which is very uncharacteristic for collective nuclei. These results were compared to state-of-the-art beyond-mean-field calculations. Conclusions: Although theoretical results give satisfactory results for the energy of the first few excited states in 170Os and the B(E2; 2+ 1 → 0+ 1 ) they fail to reproduce the very small B(E2; 4+ 1 → 2+ 1 ), which remains a puzzle

Nuclear structure with radioactive muonic atoms

Muonic atoms have been used to extract the most accurate nuclear charge radii based on the detection of X-rays from the muonic cascades. Most stable and a few un- stable isotopes have been investigated with muonic atom spectroscopy techniques. A new research project recently started at the Paul Scherrer Institut aims to extend the high- resolution muonic atom spectroscopy for the precise determination of nuclear charge radii and other nuclear structure properties of radioactive isotopes. The challenge to combine the high-energy muon beam with small quantity of stopping mass is being addressed by developing the concept of stopping the muon in a high-density, a high-pressure hydrogen cell and subsequent transfer of the muon to the element of interest. Status and perspectives of the project will be presented.status: Published onlin

A Novel Nuclear Emulsion Detector for Measurement of Quantum States of Ultracold Neutrons in the Earth's Gravitational Field

Hypothetical short-range interactions could be detected by measuring the wavefunctions of ultracold neutrons (UCNs) on a mirror bounded by the Earth's gravitational field. The Searches require detectors with higher spatial resolution. We are developing a UCN detector for the with a high spatial resolution, which consists of a Si substrate, a thin converter layer including $^{10}$B$_{4}$C, and a layer of fine-grained nuclear emulsion. Its resolution was estimated to be less than 100 nm by fitting tracks of either $^{7}$Li nuclei or $\alpha$-particles, which were created when neutrons interacted with the $^{10}$B$_{4}$C layer. For actual measurements of the spatial distributions, the following two improvements were made: The first was to establish a method to align microscopic images with high accuracy within a wide region of 65 mm $\times$ 0.2 mm. We created reference marks of 1 $\mu$m and 5 $\mu$m diameter with an interval of 50 $\mu$m and 500 $\mu$m, respectively, on the Si substrate by electron beam lithography and realized a position accuracy of less than 30 nm. The second was to build a holder that could maintain the atmospheric pressure around the nuclear emulsion to utilize it under vacuum during exposure to UCNs. The intrinsic resolution of the improved detector was estimated by evaluating the blur of a transmission image of a gadolinium grating taken by cold neutrons as better than 0.56 $\pm$ 0.08 $\mu$m, which included the grating accuracy. A test exposure to UCNs was conducted to obtain the spatial distribution of UCNs in the Earth's gravitational field. Although the test was successful, a blurring of 6.9 $\mu$m was found in the measurements, compared with a theoretical curve. We identified the blurring caused by the refraction of UCNs due to the roughness of the upstream surface of the substrate. Polishing of the surface makes the resolution less than 100 nm

Demonstration of sensitivity increase in mercury free-spin-precession magnetometers due to laser-based readout for neutron electric dipole moment searches

International audienceWe report on a laser based $^{199}$Hg co-magnetometer deployed in an experiment searching for a permanent electric dipole moment of the neutron. We demonstrate a more than five times increased signal to-noise-ratio in a direct comparison measurement with its $^{204}$Hg discharge bulb-based predecessor. An improved data model for the extraction of important system parameters such as the degrees of absorption and polarization is derived. Laser- and lamp-based data-sets can be consistently described by the improved model which permits to compare measurements using the two different light sources and to explain the increase in magnetometer performance. The laser-based magnetometer satisfies the magnetic field sensitivity requirements for the next generation nEDM experiments

Erratum to: Data blinding for the nEDM experiment at PSI

ISSN:1434-6001ISSN:1434-601