arXiv subjects

J. Stewart

Publications and source records attributed to J. Stewart.

12 recordsLinked to original sources

arXiv2022

Parameterization of Electron Attachment Rate Constants for Common Impurities in LArTPC Detectors

The ability of free electrons to drift long distances at high velocities in pure liquid argon under an applied electric field has been exploited for the past forty years to implement detectors with increasingly large volumes for high energy physics research. In this paper, we summarize the electron attachment rate constants as a function of the external electric field for common impurities in LArTPC with data from the literature. We further provide analytical functions to parameterize the data, which are useful to compare with new measurements as well as to make extrapolations.

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

Oscillatory reconnection and waves driven by merging magnetic flux ropes in solar flares

Oscillatory reconnection is a process that has been suggested to underlie several solar and stellar phenomena, and is likely to play an important role in transient events such as flares. Quasi-periodic pulsations (QPPs) in flare emissions may be a manifestation of oscillatory reconnection, but the underlying mechanisms remain uncertain. In this paper, we present 2D magnetohydrodynamic (MHD) simulations of two current-carrying magnetic flux ropes with an out-of-plane magnetic field undergoing oscillatory reconnection in which the two flux ropes merge into a single flux rope. We find that oscillatory reconnection can occur intrinsically without an external oscillatory driver during flux rope coalescence, which may occur both during large-scale coronal loop interactions and the merging of plasmoids in fragmented current sheets. Furthermore, we demonstrate that radially propagating non-linear waves are produced in the aftermath of flux rope coalescence, due to the post-reconnection oscillations of the merged flux rope. The behaviour of these waves is found to be almost independent of the initial out-of-plane magnetic field. It is estimated that the waves emitted through merging coronal loops and merging plasmoids in loop-top current sheets would have a typical phase speed of 90 km/s and 900 km/s respectively. It is possible that the properties of the waves emitted during flux rope coalescence could be used as a diagnostic tool to determine physical parameters within a coalescing region.

astro-ph.SR↗

arXiv2022

Cryogenic User Facilities for R&D on Noble Liquid Detectors and Low Temperature Devices

Cryogenic test facilities are critical infrastructure for physics experiments in a variety of fields, perhaps most notably for particle detection with noble liquid detectors, low-temperature device development, and quantum information research. However, considerable investment and technical knowledge are required to construct and operate such facilities. This white paper discusses proposals for user facilities aimed at broadening the availability of testing capabilities for the scientific community.

physics.ins-det↗

arXiv2020

Design and performance of a 35-ton liquid argon time projection chamber as a prototype for future very large detectors

Liquid argon time projection chamber technology is an attractive choice for large neutrino detectors, as it provides a high-resolution active target and it is expected to be scalable to very large masses. Consequently, it has been chosen as the technology for the first module of the DUNE far detector. However, the fiducial mass required for "far detectors" of the next generation of neutrino oscillation experiments far exceeds what has been demonstrated so far. Scaling to this larger mass, as well as the requirement for underground construction places a number of additional constraints on the design. A prototype 35-ton cryostat was built at Fermi National Acccelerator Laboratory to test the functionality of the components foreseen to be used in a very large far detector. The Phase I run, completed in early 2014, demonstrated that liquid argon could be maintained at sufficient purity in a membrane cryostat. A time projection chamber was installed for the Phase II run, which collected data in February and March of 2016. The Phase II run was a test of the modular anode plane assemblies with wrapped wires, cold readout electronics, and integrated photon detection systems. While the details of the design do not match exactly those chosen for the DUNE far detector, the 35-ton TPC prototype is a demonstration of the functionality of the basic components. Measurements are performed using the Phase II data to extract signal and noise characteristics and to align the detector components. A measurement of the electron lifetime is presented, and a novel technique for measuring a track's position based on pulse properties is described.

physics.ins-det↗

arXiv2018

First Observation of $P$-odd $γ$ Asymmetry in Polarized Neutron Capture on Hydrogen

We report the first observation of the parity-violating 2.2 MeV gamma-ray asymmetry $A^{np}_γ$ in neutron-proton capture using polarized cold neutrons incident on a liquid parahydrogen target at the Spallation Neutron Source at Oak Ridge National Laboratory. $A^{np}_γ$ isolates the $ΔI=1$, \mbox{$^{3}S_{1}\rightarrow {^{3}P_{1}}$} component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to a single coupling constant in either the DDH meson exchange model or pionless EFT. We measured $A^{np}_γ= [-3.0 \pm 1.4 (stat) \pm 0.2 (sys)]\times 10^{-8}$, which implies a DDH weak $πNN$ coupling of $h_π^{1} = [2.6 \pm 1.2(stat) \pm 0.2(sys)] \times 10^{-7}$ and a pionless EFT constant of $C^{^{3}S_{1}\rightarrow ^{3}P_{1}}/C_{0}=[-7.4 \pm 3.5 (stat) \pm 0.5 (sys)] \times 10^{-11}$ MeV$^{-1}$. We describe the experiment, data analysis, systematic uncertainties, and the implications of the result.

nucl-ex↗

arXiv2018

Photon detector system timing performance in the DUNE 35-ton prototype liquid argon time projection chamber

The 35-ton prototype for the Deep Underground Neutrino Experiment far detector was a single-phase liquid argon time projection chamber with an integrated photon detector system, all situated inside a membrane cryostat. The detector took cosmic-ray data for six weeks during the period of February 1, 2016 to March 12, 2016. The performance of the photon detection system was checked with these data. An installed photon detector was demonstrated to measure the arrival times of cosmic-ray muons with a resolution better than 32 ns, limited by the timing of the trigger system. A measurement of the timing resolution using closely-spaced calibration pulses yielded a resolution of 15 ns for pulses at a level of 6 photo-electrons. Scintillation light from cosmic-ray muons was observed to be attenuated with increasing distance with a characteristic length of $155 \pm 28$ cm.

physics.ins-det↗

arXiv2017

Natural mortality of Trachurus novaezelandiae and their size selection by purse seines off south-eastern Australia

The natural mortality (M) and purse-seine catchability and selectivity were estimated for Trachurus novaezelandiae, Richardson, 1843 (yellowtail scad)-a small inshore pelagic species harvested off south-eastern Australia. Hazard functions were applied to two decades of data describing catches (mostly stable at a mean +- SE of 315 +- 14 t p.a.) and effort (declining from a maximum of 2289 to 642 boat days between 1999/00 and 2015/16) and inter-dispersed (over nine years) annual estimates of size-at-age (0+ to 18 years) to enable survival analysis. The data were best described by a model with eight parameters, including catchability (estimated at < 0.1 x 10-7 boat day-1), M (0.22 year-1) and variable age-specific selection up to 6 years with a 50% retention among 5-year olds (larger than the estimated age at maturation). The low catchability implied minimal fishing mortality by the purse-seine fleet. Ongoing monitoring and applied gear-based studies are required to validate purse-seine catchability and selectivity, but the data nevertheless imply T. novaezelandiae could incur substantial additional fishing effort and, in doing, so alleviate pressure on other regional small pelagics.

q-bio.PE↗

arXiv2014

Beam-helicity asymmetry in associated electroproduction of real photons $ep \to eγπN$ in the $Δ$-resonance region

The beam-helicity asymmetry in associated electroproduction of real photons, $ep\to eγπN$, in the $Δ$(1232)-resonance region is measured using the longitudinally polarized HERA positron beam and an unpolarized hydrogen target. Azimuthal Fourier amplitudes of this asymmetry are extracted separately for two channels, $ep\to eγπ^0 p$ and $ep\to eγπ^+ n$, from a data set collected with a recoil detector. All asymmetry amplitudes are found to be consistent with zero.

hep-ex↗

arXiv2013

Precision Neutrino Oscillation Measurements using Simultaneous High-Power, Low-Energy Project-X Beams

The first phase of the long-baseline neutrino experiment, LBNE10, will use a broadband, high-energy neutrino beam with a 10-kt liquid argon TPC at 1300 km to study neutrino oscillation. In this paper, we describe potential upgrades to LBNE10 that use Project X to produce high-intensity, low-energy neutrino beams. Simultaneous, high-power operation of 8- and 60-GeV beams with a 200-kt water Cerenkov detector would provide sensitivity to nu_mu to nu_e oscillations at the second oscillation maximum. We find that with ten years of data, it would be possible to measure sin2(2theta_13) with precision comparable to that expected from reactor antineutrino disappearance and to measure the value of the CP phase, delta_CP, with an uncertainty of (5-10) degrees. This document is submitted for inclusion in Snowmass 2013.

hep-ex↗

arXiv2013

The HERMES Recoil Detector

For the final running period of HERA, a recoil detector was installed at the HERMES experiment to improve measurements of hard exclusive processes in charged-lepton nucleon scattering. Here, deeply virtual Compton scattering is of particular interest as this process provides constraints on generalised parton distributions that give access to the total angular momenta of quarks within the nucleon. The HERMES recoil detector was designed to improve the selection of exclusive events by a direct measurement of the four-momentum of the recoiling particle. It consisted of three components: two layers of double-sided silicon strip sensors inside the HERA beam vacuum, a two-barrel scintillating fibre tracker, and a photon detector. All sub-detectors were located inside a solenoidal magnetic field with an integrated field strength of 1 T. The recoil detector was installed in late 2005. After the commissioning of all components was finished in September 2006, it operated stably until the end of data taking at HERA end of June 2007. The present paper gives a brief overview of the physics processes of interest and the general detector design. The recoil detector components, their calibration, the momentum reconstruction of charged particles, and the event selection are described in detail. The paper closes with a summary of the performance of the detection system.

physics.ins-det↗

arXiv2012

Neutrino Oscillations in the Precision Era

With the discovery of a modest size for the mixing angle $θ_{13} \sim 9^\circ$ by the Daya Bay collaboration at $>$5 sigma (\cite{dayabay}) the science of neutrino oscillations has shifted to explicit demonstration of CP violation and precision determination of the CP phase in the 3-flavor framework. Any additional contributions from new physics to the oscillation channel $ν_μ\to ν_e$ could be uncovered by multiple constraints in the ($θ_{13}, δ_{CP}$) parameter space. In long-baseline experiments such constraints will require examination of the oscillation strength at higher $L/E$ where the effects of CP violation will be large. For the fixed baseline of 1300 km for the Long-Baseline Neutrino Experiment (LBNE, Fermilab to Homestake), it will be important to examine oscillations at low energies ($<1.5$ GeV) with good statistics, low backgrounds, and excellent energy resolution. The accelerator upgrades in the Project-X era have the potential to offer the beams of the needed intensity and quality for this advanced science program. In this paper we examine the event rates for high intensity, low energy running of Project-X and the Fermilab Main Injector complex, and the precision in the ($θ_{13}, δ_{CP}$) space. In this paper we have examined the baseline distance of 1300 km in detail, however we point out that much longer distances such as 2500 km should also be exmained with a beam from FNAL in light of the new understanding of the neutrino mixing.

hep-ex↗