arXiv subjects

W. M. Snow

Publications and source records attributed to W. M. Snow.

At least 37 records · Page 2Linked to original sources

arXiv2023

COHERENT Collaboration data release from the measurements of CsI[Na] response to nuclear recoils

Description of the data release 10.13139/OLCF/1969085 (https://doi.ccs.ornl.gov/ui/doi/426) from the measurements of the CsI[Na] response to low energy nuclear recoils by the COHERENT collaboration. The release corresponds to the results published in "D. Akimov et al 2022 JINST 17 P10034". We share the data in the form of raw ADC waveforms, provide benchmark values, and share plots to enhance the transparency and reproducibility of our results. This document describes the contents of the data release as well as guidance on the use of the data.

physics.ins-det↗

arXiv2023

A Complete Approach to Determine the $^3$He neutron incoherent scattering length $b_i$

We report the first results from a new approach for measuring the $^3$He neutron incoherent scattering length $b_{i}$. $b_{i}$ is directly proportional to the difference $Δb=b_{+}-b_{-}$ in the two low-energy s-wave neutron-nucleus scattering amplitudes $b_{+}$ and $b_{-}$, corresponding to the singlet $J=0$ and triplet $J=1$ states of the neutron-$^3$He interaction, respectively. An accurate measurement of $b_{i}$ can help distinguish among different models of three-nucleon interactions by comparison to {\it ab initio} nuclear theory calculations. The neutron birefringence caused by $Δb$ results in neutron spin rotation around the nuclear polarization. We measured $Δb$ using polarized neutron spin rotation and the transmission of neutrons through a $^3$He gas target polarized in situ by spin-exchange optical pumping. This brief test measurement, conducted at the FZ-Jülich neutron spin echo spectrometer at the Heinz Maier Leibnitz Zentrum (MLZ), yielded $Δb = [-5.27 \pm 0.05$ (stat.) $- 0.05$ (syst.)] fm. We argue that this method can be improved in precision to resolve the discrepancies between two prior measurements of $b_i$ which are dependent on the polarized absorption cross section $σ_p$. Further with absolute $^{3}$He polarization via NMR (in a properly-shaped cell) concurrent with accurate neutron transmission measurements, $σ_p$ can be measured to obtain independent values of $b_{+}$ and $b_{-}$.

nucl-ex↗

arXiv2023

P-even and -odd asymmetries on $^{117}$Sn at the vicinity of the p-resonance E$_\mathrm{p}$=1.33 eV

A self consistent description of angular correlations in neutron induced reactions is required for quantitative analysis of parity violating (PV) and time reversal invariance violating (TRIV) effects in neutron nucleus scattering. The 1.33 eV p-wave compound resonance in $^{117}$Sn is one of the few p-wave resonances where enough measurements have been performed to allow a nontrivial test of the internal consistency of the theory. We present the results of a global analysis of the several different asymmetries and angular distribution measurements in ($n, γ$) reactions on the 1.33 eV p-wave resonance in $^{117}$Sn conducted over the last few decades. We show that the compound resonance mixing theory can give an internally consistent description of all observations made in this system to date within the experimental measurement errors. We also confirm the conclusions of previous analyses that a subthreshold resonance in $^{117}$Sn dominates correlations related to s-p mixing, and discuss the implications of these results for future searches for TRIV in this system.

nucl-th↗

arXiv2023

First Probe of Sub-GeV Dark Matter Beyond the Cosmological Expectation with the COHERENT CsI Detector at the SNS

The COHERENT collaboration searched for scalar dark matter particles produced at the Spallation Neutron Source with masses between 1 and 220~MeV/c$^2$ using a CsI[Na] scintillation detector sensitive to nuclear recoils above 9~keV$_\text{nr}$. No evidence for dark matter is found and we thus place limits on allowed parameter space. With this low-threshold detector, we are sensitive to coherent elastic scattering between dark matter and nuclei. The cross section for this process is orders of magnitude higher than for other processes historically used for accelerator-based direct-detection searches so that our small, 14.6~kg detector significantly improves on past constraints. At peak sensitivity, we reject the flux consistent with the cosmologically observed dark-matter concentration for all coupling constants $α_D<0.64$, assuming a scalar dark-matter particle. We also calculate the sensitivity of future COHERENT detectors to dark-matter signals which will ambitiously test multiple dark-matter spin scenarios.

hep-ex↗

arXiv2023

First Measurement of Neutron Birefringence in Polarized $^{129}$Xe and $^{131}$Xe Nuclei

We present the first measurements of polarized neutron birefringence in transmission through nuclear-polarized $^{129}$Xe and $^{131}$Xe gas and determine the neutron incoherent scattering lengths $b_i(^{129}Xe)=0.186\pm(0.021)_{stat.}\pm(0.004)_{syst.}\space\text{ fm}$ and $b_i(^{131}Xe)=2.09\pm(0.29)_{stat.}\pm(0.12)_{syst.}\space\text{ fm}$ for the first time. These results determine the essential parameter needed for interpretation of spin-dependent neutron-scattering studies on polarized xenon ensembles, with possible future applications ranging from tests of time-reversal violation to mode-entangled neutron scattering experiments on nuclear-polarized systems.

nucl-ex↗

arXiv2022

Angular distribution of $γ$-rays from a neutron-induced $p$-wave resonance of $^{132}$Xe

A neutron-energy dependent angular distribution was measured for individual $γ$-rays from the 3.2 eV $p$-wave resonance of $^{131}$Xe+$n$, that shows enhanced parity violation owing to a mixing between $s$- and $p$-wave amplitudes. The $γ$-ray transitions from the $p$-wave resonance were identified, and the angular distribution with respect to the neutron momentum was evaluated as a function of the neutron energy for 7132 keV $γ$-rays, which correspond to a transition to the 1807 keV excited state of $^{132}$Xe. The angular distribution is considered to originate from the interference between $s$- and $p$-wave amplitudes, and will provide a basis for a quantitative understanding of the enhancement mechanism of the fundamental parity violation in compound nuclei.

nucl-ex↗

arXiv2022

Measurement of scintillation response of CsI[Na] to low-energy nuclear recoils by COHERENT

We present results of several measurements of CsI[Na] scintillation response to 3-60 keV energy nuclear recoils performed by the COHERENT collaboration using tagged neutron elastic scattering experiments and an endpoint technique. Earlier results, used to estimate the coherent elastic neutrino-nucleus scattering (CEvNS) event rate for the first observation of this process achieved by COHERENT at the Spallation Neutron Source (SNS), have been reassessed. We discuss corrections for the identified systematic effects and update the respective uncertainty values. The impact of updated results on future precision tests of CEvNS is estimated. We scrutinize potential systematic effects that could affect each measurement. In particular we confirm the response of the H11934-200 Hamamatsu photomultiplier tube (PMT) used for the measurements presented in this study to be linear in the relevant signal scale region.

physics.ins-det↗

arXiv2022

Comments on Systematic Effects in the NIST Beam Neutron Lifetime Experiment

We discuss issues raised by Serebrov, et al. in a recent paper regarding systematic effects in the beam neutron lifetime experiment performed at NIST. We show that these effects were considered in the original analyses and that our corrections and systematic uncertainties were appropriate. We point out some misconceptions and erroneous assumptions in the analysis of Serebrov, et al. None of the issues raised in Serebrov, et al lead us to alter the value of the neutron lifetime reported previously.

nucl-ex↗

arXiv2022

The Development of the NNBAR Experiment

The NNBAR experiment for the European Spallation Source will search for free neutrons converting to antineutrons with a sensitivity improvement of three orders of magnitude compared to the last such search. This paper describes progress towards a conceptual design report for NNBAR. The design of a moderator, neutron reflector, beamline, shielding and annihilation detector is reported. The simulations used form part of a model which will be used for optimisation of the experiment design and quantification of its sensitivity.

physics.ins-det↗

arXiv2022

Measurement of the Parity-Odd Angular Distribution of Gamma Rays From Polarized Neutron Capture on $^{35}$Cl

We report a measurement of two energy-weighted gamma cascade angular distributions from polarized slow neutron capture on the ${}^{35}$Cl nucleus, one parity-odd correlation proportional to $\vec{s_{n}} \cdot \vec{k_γ}$ and one parity-even correlation proportional to $\vec{s_{n}} \cdot \vec{k_{n}} \times \vec{k_γ}$. A parity violating asymmetry can appear in this reaction due to the weak nucleon-nucleon (NN) interaction which mixes opposite parity S and P-wave levels in the excited compound $^{36}$Cl nucleus formed upon slow neutron capture. If parity-violating (PV) and parity-conserving (PC) terms both exist, the measured differential cross section can be related to them via $\frac{dσ}{dΩ}\propto1+A_{γ, PV}\cosθ+A_{γ,PC}\sinθ$. The PV and PC asymmetries for energy-weighted gamma cascade angular distributions for polarized slow neutron capture on $^{35}$Cl averaged over the neutron energies from 2.27~meV to 9.53~meV were measured to be $A_{γ,PV}=(-23.9\pm0.7)\times 10^{-6}$ and $A_{γ,PC}=(0.1\pm0.7)\times 10^{-6}$. These results are consistent with previous experimental results. Systematic errors were quantified and shown to be small compared to the statistical error. These asymmetries in the angular distributions of the gamma rays emitted from the capture of polarized neutrons in $^{35}$Cl were used to verify the operation and data analysis procedures for the NPDGamma experiment which measured the parity-odd asymmetry in the angular distribution of gammas from polarized slow neutron capture on protons.

nucl-ex↗

arXiv2022

Measurement of the Coherent Elastic Neutrino-Nucleus Scattering Cross Section on CsI by COHERENT

We measured the cross section of coherent elastic neutrino-nucleus scattering (\cevns{}) using a CsI[Na] scintillating crystal in a high flux of neutrinos produced at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. New data collected before detector decommissioning has more than doubled the dataset since the first observation of \cevns{}, achieved with this detector. Systematic uncertainties have also been reduced with an updated quenching model, allowing for improved precision. With these analysis improvements, the COHERENT collaboration determined the cross section to be $(165^{+30}_{-25})\times10^{-40}$~cm$^2$, consistent with the standard model, giving the most precise measurement of \cevns{} yet. The timing structure of the neutrino beam has been exploited to compare the \cevns{} cross section from scattering of different neutrino flavors. This result places leading constraints on neutrino non-standard interactions while testing lepton flavor universality and measures the weak mixing angle as $\sin^2θ_{W}=0.220^{+0.028}_{-0.026}$ at $Q^2\approx(50\text{ MeV})^2$

hep-ex↗

arXiv2022

A COHERENT constraint on leptophobic dark matter using CsI data

We use data from the COHERENT CsI[Na] scintillation detector to constrain sub-GeV leptophobic dark matter models. This detector was built to observe low-energy nuclear recoils from coherent elastic neutrino-nucleus scattering. These capabilities enable searches for dark matter particles produced at the Spallation Neutron Source mediated by a vector portal particle with masses between 2 and 400 MeV/c$^2$. No evidence for dark matter is observed and a limit on the mediator coupling to quarks is placed. This constraint improves upon previous results by two orders of magnitude. This newly explored parameter space probes the region where the dark matter relic abundance is explained by leptophobic dark matter when the mediator mass is roughly twice the dark matter mass. COHERENT sets the best constraint on leptophobic dark matter at these masses.

hep-ex↗

arXiv2022

Imaging of PbWO4 Crystals for G Experiment Test Masses Using a Laser Interferometer

It is highly desirable for future measurements of Newton's gravitational constant $G$ to use test/source masses that allow nondestructive, quantitative internal density gradient measurements. High density optically transparent materials are ideally suited for this purpose since their density gradient can be measured with laser interferometry, and they allow in-situ optical metrology methods for the critical distance measurements often needed in a $G$ apparatus. We present an upper bound on possible internal density gradients in lead tungstate (PbWO$_4$) crystals determined using a laser interferometer. We placed an upper bound on the fractional atomic density gradient in two PbWO$_4$ test crystals of ${1 \over ρ}{dρ\over dx}<2.1 \times 10^{-8}$ cm$^{-1}$. This value is more than two orders of magnitude smaller than what is required for $G$ measurements. They are also consistent with but more sensitive than a recently reported measurements of the same samples, using neutron interferometry. These results indicate that PbWO$_4$ crystals are well suited to be used as test masses in $G$ experiments. Future measurements of internal density gradients of test masses used for measurements of $G$ can now be conducted non-destructively for a wide range of possible test masses.

physics.ins-det↗

arXiv2022

Monitoring the SNS basement neutron background with the MARS detector

We present the analysis and results of the first dataset collected with the MARS neutron detector deployed at the Oak Ridge National Laboratory Spallation Neutron Source (SNS) for the purpose of monitoring and characterizing the beam-related neutron (BRN) background for the COHERENT collaboration. MARS was positioned next to the COH-CsI coherent elastic neutrino-nucleus scattering detector in the SNS basement corridor. This is the basement location of closest proximity to the SNS target and thus, of highest neutrino flux, but it is also well shielded from the BRN flux by infill concrete and gravel. These data show the detector registered roughly one BRN per day. Using MARS' measured detection efficiency, the incoming BRN flux is estimated to be $1.20~\pm~0.56~\text{neutrons}/\text{m}^2/\text{MWh}$ for neutron energies above $\sim3.5$ MeV and up to a few tens of MeV. We compare our results with previous BRN measurements in the SNS basement corridor reported by other neutron detectors.

physics.ins-det↗

arXiv2022

The COHERENT Experimental Program

The COHERENT experiment located in Neutrino Alley at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory (ORNL), has made the world's first two measurements of coherent elastic neutrino-nucleus scattering (CEvNS), on CsI and argon, using neutrinos produced at the SNS. The COHERENT collaboration continues to pursue CEvNS measurements on various targets as well as additional studies of inelastic neutrino-nucleus interactions, searches for accelerator-produced dark matter (DM) and physics beyond the Standard Model, using the uniquely high-quality and high-intensity neutrino source available at the SNS. This white paper describes primarily COHERENT's ongoing and near-future program at the SNS First Target Station (FTS). Opportunities enabled by the SNS Second Target Station (STS) for the study of neutrino physics and development of novel detector technologies are elaborated in a separate white paper.

hep-ex↗

arXiv2022

Simulating the neutrino flux from the Spallation Neutron Source for the COHERENT experiment

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is a pulsed source of neutrons and, as a byproduct of this operation, an intense source of pulsed neutrinos via stopped-pion decay. The COHERENT collaboration uses this source to investigate coherent elastic neutrino-nucleus scattering and other physics with a suite of detectors. This work includes a description of our Geant4 simulation of neutrino production at the SNS and the flux calculation which informs the COHERENT studies. We estimate the uncertainty of this calculation at about 10% based on validation against available low-energy pion production data.

hep-ex↗

arXiv2022

New Horizons: Scalar and Vector Ultralight Dark Matter

The last decade has seen unprecedented effort in dark matter model building at all mass scales coupled with the design of numerous new detection strategies. Transformative advances in quantum technologies have led to a plethora of new high-precision quantum sensors and dark matter detection strategies for ultralight ($<10\,$eV) bosonic dark matter that can be described by an oscillating classical, largely coherent field. This white paper focuses on searches for wavelike scalar and vector dark matter candidates.

hep-ex↗

arXiv2021

Neutron Phase Contrast Imaging of PbWO$_{4}$ Crystals for G Experiment Test Masses Using a Talbot-Lau Neutron Interferometer

The use of transparent test/source masses can benefit future measurements of Newton's gravitational constant $G$. Such transparent test mass materials can enable nondestructive, quantitative internal density gradient measurements using optical interferometry and allow in-situ optical metrology methods to be realized for the critical distance measurements often needed in a $G$ apparatus. To confirm the sensitivity of such optical interferometry measurements to internal density gradients it is desirable to conduct a check with a totally independent technique. We present an upper bound on possible internal density gradients in lead tungstate (PbWO$_4$) crystals using a Talbot-Lau neutron interferometer on the Cold Neutron Imaging Facility (CNIF) at NIST. We placed an upper bound on a fractional atomic density gradient in two PbWO$_{4}$ test crystals of ${1 \over N}{dN \over dx}<0.5 \times 10^{-6}$ cm$^{-1}$. This value is about two orders of magnitude smaller than required for $G$ measurements. We discuss the implications of this result and of other nondestructive methods for characterization of internal density inhomogeneties which can be applied to test masses in $G$ experiments.

physics.ins-det↗