arXiv subjects

W. Michael Snow

Publications and source records attributed to W. Michael Snow.

9 recordsLinked to original sources

arXiv2026

Torsion and Nonmetricity Constraints From Neutron Spin Rotation in Polarized Matter

Many modified-gravity frameworks employ non-Riemannian connection degrees of freedom, including torsion and nonmetricity. In Einstein-Cartan-type theories, torsion is associated with spin density, while more general metric-affine frameworks can be investigated through phenomenological searches for in-matter torsion and nonmetricity backgrounds. This work applies an effective field theory approach to characterize general couplings of electron and neutron operators to spacetime torsion and nonmetricity up to mass dimension six, predicting novel neutron-polarization signatures in the presence of an electron background. Neutron spin-rotation data from a polarized-electron ensemble inside a compensated ferrimagnet are used to constrain for the first time axially symmetric, direction-dependent in-matter torsion and nonmetricity combinations.

gr-qc↗

arXiv2026

Hadronic parity violation: successes, challenges, and future prospects

Hadronic parity violation concerns the study of the interplay of the weak- and strong-interaction dynamics that yields low energy, parity-violating observables in systems of hadrons and nuclei. We explain its essential features, as well as our current understanding of its observed effects, describing recent theoretical and experimental progress in a pedagogical context. We provide a broad overview of ongoing research efforts to show how precision studies of few-nucleon systems can be extended to studies of complex nuclei and, ultimately, to new benchmarks for computations in the Standard Model, as well as to new searches for the dynamics beyond it.

nucl-th↗

arXiv2024

First Use of a Polarized $^3$He Neutron Spin Filter on the Back-n White Neutron Source of CSNS

Polarized eV neutrons can address interesting scientific questions in nuclear physics, particle physics, and astrophysics/cosmology. We present the first experiment to polarize the neutrons on the Back-n beamline at the Chinese Spallation Neutron Source (CSNS) using an in-situ NSF using spin-exchange optical pumping (SEOP) of 3He. A 3He polarization of 68%$\pm$0.7% for this in-situ NSF was measured through neutron transmission method at Back-n.This is high enough to enable new experiments on the Back-n beamline. Polarized neutron, Polarized nuclei, CSNS, White neutron, Fundamental physics research PACS number(s): 24.80.+y, 67.30.ep, 29.27.Hj , 24.70.+s , 32.10.Dk

nucl-ex↗

arXiv2021

Two-Orders-of-Magnitude Improvement in the Total Spin Angular Momentum of 131Xe Nuclei Using Spin Exchange Optical Pumping

We report on hyperpolarization of quadrupolar (I=3/2) 131Xe via spin-exchange optical pumping. Observations of the 131Xe polarization dynamics show that the effective alkali-metal/131Xe spin-exchange cross-sections are large enough to compete with 131Xe spin relaxation. 131Xe polarization up to 7.6 p/m 1.5 percent was achieved in ca. 8.5EE20 spins--a ca. 100-fold improvement in the total spin angular momentum--enabling applications including measurement of spin-dependent neutron-131Xe s-wave scattering and sensitive searches for time-reversal violation in neutron-131Xe interactions beyond the Standard Model.

physics.atom-ph↗

arXiv2021

Compact ultracold neutron source concept for low energy accelerator-driven neutron sources

The concept of a small-scale, pulsed-proton accelerator based compact ultracold neutron (UCN) source is presented. The essential idea of the compact UCN source is to enclose a volume of superfluid $^{4}\mathrm{He}$ converter with a supercold moderator in the vicinity of a low-radiation neutron production target from (p, n) reactions. The supercold moderator should possess an ability to produce cold neutron flux with a peak brightness near the single-phonon excitation band of the superfluid $^{4}\mathrm{He}$ converter, thereby augmenting the UCN production in the compact UCN source even with very low intensity of neutron brightness. The performance of the compact UCN source is studied in terms of the UCN production and thermal load in the UCN converter. With the proposed concept of the compact UCN source, a UCN production rate of $P_{\mathrm{UCN}}=80\mathrm{UCN}/\mathrm{cc}/\mathrm{sec}$ in the UCN converter could be obtained while maintaining thermal load of on the superfluid $^{4}\mathrm{He}$ and its container at a level of $22\mathrm{mW}$. This study shows that the compact UCN source can produce a high enough density of UCN at a small-scale, low-energy, pulsed-proton beam facility with reduced efforts on the cooling and radiation protection.

physics.ins-det↗

arXiv2019

An Operator Analysis of Contextuality Witness Measurements for Multimode-Entangled Single Neutron Interferometry

We develop an operator-based description of two types of multimode-entangled single-neutron quantum optical devices: Wollaston prisms and radio-frequency spin flippers in inclined magnetic field gradients. This treatment is similar to the approach used in quantum optics, and is convenient for the analysis of quantum contextuality measurements in certain types of neutron interferometers. We describe operationally the way multimode-entangled single-neutron states evolve in these devices, and provide expressions for the associated operators describing the dynamics, in the limit in which the neutron state space is approximated by a finite tensor product of distinguishable subsystems. We design entangled-neutron interferometers to measure entanglement witnesses for the Clauser, Horne, Shimony and Holt, and Mermin inequalities, and compare the theoretical predictions with recent experimental results. We present the generalization of these expressions to $n$ entangled distinguishable subsystems, which could become relevant in the future if it becomes possible to add neutron orbital angular momentum to the experimentally-accessible list of entangled modes. We view this work as a necessary first step towards a theoretical description of entangled neutron scattering from strongly entangled matter, and we explain why it should be possible to formulate a useful generalization of the usual Van Hove linear response theory for this case. We also briefly describe some other scientific extensions and applications which can benefit from interferometric measurements using the types of single-neutron multimode entanglement described by this analysis.

quant-ph↗

arXiv2019

Measurement of the total neutron scattering cross section ratios of noble gases of natural isotopic composition using a pulsed neutron beam

Precision measurements of slow neutron cross sections with atoms have several scientific applications. In particular the n-$^{4}$He s-wave scattering length is important to know both for helping to constrain the nuclear three-body interaction and for the proper interpretation of several ongoing slow neutron experiments searching for other types of neutron-atom interactions. We present new measurements of the ratios of the neutron differential scattering cross sections for natural isotopic-abundance mixtures of the noble gases He, Ar, Kr, and Xe to natural isotopic abundance Ne. These measurements were performed using a recently developed neutron scattering apparatus for gas samples located on a pulsed slow neutron beamline which was designed to search for possible exotic neutron-atom interactions and employs both neutron time of flight information and a position-sensitive neutron detector for scattering event reconstruction. We found agreement with the literature values of scattering cross sections inferred from Ar/Ne, Kr/Ne and Xe/Ne differential cross section ratios over the $q$ range of $1 - 7$ nm$^{-1}$. However for the case of He/Ne we find that the cross section inferred differs by 11.3% (7.6 $σ$) from previously-reported values inferred from neutron phase shift measurements, but is in reasonable agreement with values from other measurements. The very large discrepancy in the He/Ne ratio calls for a new precision measurement of the n-$^{4}$He scattering length using neutron interferometry.

nucl-ex↗

arXiv2018

A Search for deviations from the inverse square law of gravity at nm range using a pulsed neutron beam

We describe an experimental search for deviations from the inverse square law of gravity at the nanometer length scale using neutron scattering from noble gases on a pulsed slow neutron beamline. By measuring the neutron momentum transfer ($q$) dependence of the differential cross section for xenon and helium and comparing to their well-known analytical forms, we place an upper bound on the strength of a new interaction as a function of interaction length $λ$ which improves upon previous results in the region $λ< 0.1\,$nm, and remains competitive in the larger $λ$ region. A pseudoexperimental simulation developed for this experiment and its role in the data analysis described. We conclude with plans for improving sensitivity in the larger $λ$ region.

nucl-ex↗

arXiv2017

Slotted Rotatable Target Assembly Used In a Search for Possible Long Range Spin Dependent Interactions From Vector Boson Exchange Using Polarized Slow Neutrons

We discuss the design and construction of a novel target array of nonmagnetic test masses used in a neutron polarimetry measurement made in search for new possible exotic spin dependent neutron-atom interactions of Nature at sub\,-$mm$ length scales. This target was designed to accept and efficiently transmit a transversely polarized slow neutron beam through a series of long open parallel slots bounded by flat rectangular plates. These openings possessed equal atom density gradients across the slots from the flat test masses with dimensions optimized to achieve maximum sensitivity to an exotic spin-dependent interaction from vector boson exchanges with ranges in the millimeter to micron regime. The parallel slots were oriented differently in four quadrants that can be rotated about the neutron beam axis using a Geneva drive. The spin rotation signals from the 4 quadrants were measured using a segmented neutron ion chamber in parallel to suppress possible systematic errors from stray magnetic fields in the target region. Design constraints and systematic effects are discussed.

physics.ins-det↗