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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

AI-Optimized Polarization at Jefferson Lab

The AI-Optimized Polarization project seeks to develop experimental control applications for polarized targets and beams at Jefferson Lab using AI/ML. This paper will focus on two ongoing efforts involving a cryogenic polarized target and a linearly-polarized photon beam. Firstly, cryogenic targets, such as those used in Halls B and C (and approved for Hall D), are complex systems that are sensitive to a number of factors, including the temperature, beam currents, and the microwave and NMR apparatus. Secondly, the Hall D photon beam polarization depends on the optimal orientation of a diamond radiator, which produces coherent bremsstrahlung radiation from the electron beam incident upon it. Manual operation of both systems is tedious and error prone; implementing well-designed, interpretable control systems that incorporate AI is expected to lead to improved real-time polarization. AI optimization of nuclear physics experiments will lead, not just to cost-savings, but also to more efficient and higher-quality data, and this project will help to lay the foundation for future autonomous experiments.

Moran, Patrick [College of William and Mary, Willi↗
DOE OSTI2020

Enhanced tensor polarization in solid-state targets

In this work, we report measurements of enhanced tensor polarization on solid-state targets. The results here represent an increase in tensor polarization over that previously achieved in high energy and nuclear scattering experiments that focused on the measurement of tensor polarized observables. Enhancement techniques are used which require RF produced close to the Larmor frequency of the target spins and use selective semi-saturation resulting from two sources of irradiation, microwave for the DNP process and the additional RF used to manipulate the population of the energy levels in the target material. The spin dynamics of the solid target are used to align the spins enhancing the ensemble average to improve the figure of merit of the scattering experiment. Target rotation at an optimized rate can lead to additional enhancement by applying selective semi-saturation in polycrystalline materials that possess a Pake doublet in their NMR signal.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

A Search for Polarized Thermal Emission from Directly Imaged Exoplanets and Brown Dwarf Companions to Nearby Stars

Aerosols in the atmospheres of cloudy gas giant exoplanets and brown dwarfs scatter and polarize these objects’ thermal emission. If such an object has an oblate shape or nonuniform cloud distribution, the net degree of linear polarization can show an increase ranging from several tenths of a percent to a few percent. Modern high-contrast imaging polarimeters are now poised to detect such low-polarization signals, opening up a new window into the rotational velocities and cloud properties of substellar companions to nearby stars. In this paper, we present the results of a near-IR survey searching for linearly polarized thermal emission from a sample of two planetary-mass companions and five brown dwarf companions using GPI and SPHERE-IRDIS. We probe the subpercent linear polarization regime that typifies polarized free-floating brown dwarfs and place limits on each object’s degree of linear polarization. We relate our upper limits on each target’s degree of linear polarization to its rotation rate, and place our results in the context of rotation rates measured using high-resolution spectroscopy.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1992

Circular and linear polarization inverse SAR imaging of simple deterministic targets and statistically known randomly rough surfaces using constant and varying illumination

In order to study mechanisms of scattering and their relative contributions to synthetic aperture radar (SAR) and inverse SAR images, a special measurement facility has been constructed. It can be used to generate images in which the target is illuminated from a constant direction as the receiver is rotated in azimuth, and the target is illuminated from various directions as the receiver is rotated in azimuth. The imaging system performance is discussed, and images obtained using both approaches are compared, for a variety of simple targets and statistically known randomly rough surfaces.

Bredow, J. W.↗
NASA NTRS1988

Polarimetric microwave scattering from known randomly rough surfaces

Scattering from rough surfaces is reviewed, and artificial randomly rough surfaces are described. Measurements were made from 4 to 18 GHz for the 4 linear polarization states. The target consists of a metalized randomly rough surface constructed from known surface statistical information. The surface was generated using surface generation routines on the computer, and then the data was converted for the machining of the surface on a computer controlled mill. Bistatic and monostatic measurements were acquired at incident angles from 25 to 60 deg. At the 13.5 to 18 GHz frequencies, the effects of backscatter enhancement and depolarization effects can be studied in a regime which does not satisfy Kirchoff or small perturbation assumptions. This allows scattering mechanisms to be introduced into models, which may show missing elements in the more standard formulations. At lower frequency bands such as 4 to 8.5 GHz the scattering behavior was also examined to see the behavior as assumptions of other formulations are satisfied.

Nance, C. E.↗
NASA NTRS1985

Birds and insects as radar targets - A review

A review of radar cross-section measurements of birds and insects is presented. A brief discussion of some possible theoretical models is also given and comparisons made with the measurements. The comparisons suggest that most targets are, at present, better modeled by a prolate spheroid having a length-to-width ratio between 3 and 10 than by the often used equivalent weight water sphere. In addition, many targets observed with linear horizontal polarization have maximum cross sections much better estimated by a resonant half-wave dipole than by a water sphere. Also considered are birds and insects in the aggregate as a local radar 'clutter' source. Order-of-magnitude estimates are given for many reasonable target number densities. These estimates are then used to predict X-band volume reflectivities. Other topics that are of interest to the radar engineer are discussed, including the doppler bandwidth due to the internal motions of a single bird, the radar cross-section probability densities of single birds and insects, the variability of the functional form of the probability density functions, and the Fourier spectra of single birds and insects.

Vaughn, C. R.↗
DOE OSTI2025

Spin-Density Matrix Elements in K∗(892) Photoproduction with Recoiling Λ at GlueX

We report on the measurement of spin-density matrix elements for the K∗(892) → K+π0 photoproduction process with a recoiling Λ hyperon. The measurement used high-statistics GlueX data from photoproduction off a proton target at photon energies between 8.2 and 8.8 GeV, in a kinematic regime dominated by t-channel exchange processes. GlueX is a fixed-target experiment with a linearly polarized photon beam and a nearly 4π hermetic detector, allowing extraction of the full spin observ- ables from both the K+π0 and Λ → π−p systems. The GlueX data show clear evidence of the K∗(892) resonance in the K+π0 mass spectrum, along with additional structures at higher masses that may correspond to K∗0 or K∗2 resonances. The precise measurement of the spin-density matrix elements of the K∗(892) could serve as a standard candle for con- tinuing studies of higher-mass excited K∗ states. In addition, t-channel K∗ photoproduction differs from previous measurements of non-strange vector meson photoproduction, as it is free from Pomeron exchange and is virtually unexplored in this energy regime. Furthermore, the unprece- dented data collected by GlueX allow for investigations of correlations between the Λ polarization and the spin-density matrix elements of K∗ production, paving the way for future partial-wave analyses with full spin information involving the recoil hyperon.

Li, Hao [College of William and Mary, Williamsburg↗
NASA NTRS1973

Polarization of the light from the 3P(1)-2S(1) transition in proton beam excited helium

Measurements of the polarization of the light from the 3 1p-2 1s transition in proton beam excited Helium have shown both a proton beam energy and Helium target gas pressure dependence. Results for the linear polarization fraction range from +2.6% at 100 keV proton energy to -5.5% at 450 keV. The zero crossover occurs at approximately 225 keV. This is in good agreement with other experimental work in the field, but in poor agreement with theoretical predictions. Measurements at He target gas pressures as low as .01 mtorr show that the linear polarization fraction is still pressure dependent at .01 mtorr.

Weinhous, M. S.↗
DOE OSTI2025

Liquid metal-based polarized positron generation benchmark using the GEANT4 toolkit

In this work, we report simulation results for the positron yield and polarization of polarized electron beams incident on GaInSn and PbBi liquid metal targets. One of the proposed upgrades to 12 GeV CEBAF is the use of a continuous wave polarized positron beam for physics experiments. High-Z liquid metal jets are excellent candidates for positron production targets because they can withstand high power beams. Polarized positron beams can be generated from a primary electron beam incident to thick high-Z targets through circular polarized bremsstrahlung conversion to linearly polarized pair production. This polarization transfer from the primary electron beam has been previously demonstrated at Jefferson Lab in the PEPPo experiment with a tungsten target at relatively low energies. Here we report Geant4 simulations for 10 and 120 MeV electron beams incident on GaInSn and PbBi liquid metal targets. These simulations are compared to simulations with a solid tungsten target, as well as with unpolarized simulations using MCNP6.

Lizarraga-Rubio, Victor Manuel↗
DOE OSTI2025

Polarization observables in double neutral pion photoproduction

Abstract Measurements of target asymmetries and double-polarization observables for the reaction "Equation missing"<#comment/>are reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility (Bonn University) using the Bonn frozen-spin butanol ($$\hbox {C}_4\hbox {H}_9$$ C 4 H 9 OH) target, which provided transversely polarized protons. Linearly polarized photons were produced via bremsstrahlung off a diamond crystal. The data cover the photon energy range from "Equation missing"<#comment/>to "Equation missing"<#comment/>and nearly the complete angular range. The results have been included in the BnGa partial wave analysis. Experimental results and the fit agree very well. Observed systematic differences in the branching ratios for decays of "Equation missing"<#comment/>and$${\varDelta ^*}$$ Δ ∗ resonances are attributed to the internal structure of these excited nucleon states. Resonances which can be assigned to SU(6)$$\times $$ × O(3) two-oscillator configurations show larger branching ratios to intermediate states with non-zero intrinsic orbital angular momenta than resonances assigned to one-oscillator configurations.

Physics↗
NASA NTRS2016

Point Source Polarimetry with the Gemini Planet Imager: Sensitivity Characterization with T5.5 Dwarf Companion HD 19467 B

Detecting polarized light from self-luminous exoplanets has the potential to provide key information about rotation, surface gravity, cloud grain size, and cloud coverage. While field brown dwarfs with detected polarized emission are common, no exoplanet or substellar companion has yet been detected in polarized light. With the advent of high contrast imaging spectro-polarimeters such as GPI and SPHERE, such a detection may now be possible with careful treatment of instrumental polarization. In this paper, we present 28 minutes of H-band GPI polarimetric observations of the benchmark T5.5 companion HD 19467 B. We detect no polarization signal from the target, and place an upper limit on the degree of linear polarization of pCL99:73% less than 1:7%. We discuss our results in the context of T dwarf cloud models and photometric variability.

Gemini Planet Imager↗
DOE OSTI2025

γIn-beam angular distribution and linear polarization measurements with GRETINA using a simple energy-ordering approach

Angular distribution and linear polarization measurements are powerful tools for inferring the spins and parities of nuclear levels. In this work, the performance of the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) as a Compton polarimeter was characterized in a fusion-evaporation reaction experiment using a simple energy-ordering approach for the interaction points assigned in the signal decomposition process. A variety of multipolarities and characters for γ-ray transitions in the reaction products 25 Mg, 25 Na, and 22 Ne, formed from fusion-evaporation of an 18 O beam on a 9 Be target, were examined. The experimental angular distributions and linear polarization asymmetries were consistent with predictions using the theoretical formalism accounting for the Lorentz boost.

Angular distribution↗
DOE OSTI2021

Photoproduction of the b 1 (1235) Meson off the proton at E gamma = 6-12 GeV

The GlueX Experiment at Jefferson Lab directs a linearly polarized photon beam on a liquid hydrogen target surrounded by an almost hermetic detector. The experiment aims to study the meson spectrum in the light-quark sector and search for exotic spin-parity states predicted by lattice QCD calculations. The lightest exotic candidate is the π 1 meson, which is predicted to decay dominantly to b 1 π. In this thesis, we present efforts to characterize the ωπ 0 decay channel of the b 1 meson as precursor to an analysis of the sought-after π 1 exotic state. We present an introduction to the physics involved and an overview of the detector subsystems with a focus on the Barrel Calorimeter gain monitoring system, as part of the service work expected by the GlueX Collaboration. We discuss the data analysis method used and present two frameworks, for angular moments and partial waves analyses. Details of the simulation used to calculate the detector acceptance. A proof of concept partial wave analysis is presented along with experimental angular moments as first step to a full analysis of the angular distribution Our partial wave analysis indicates that both S- and D-waves are needed, in qualitative agreement with theoretical expectations. The cross-section of the omega π 0 channel is extracted to be of the scale of 1 μb in agreement with previous measurements. The differential cross-section indicates the presence of two production processes with p 1 = -5:24 ± 0:04 for 0:25 < -t < 0:95 GeV 2 ~c 2 and p 2 = -1:24 ± 0:05 for 0:95 < -t < 2:0 GeV 2 ~c 2 , which does not agree with results from previous experiments. The s-channel helicity conservation and helicity amplitudes of the b 1 meson are presented as additional experimental observables. Our results confirm that the b1 photoproduction process does not conserve s-channel helicity though they do not align with previous measurements. The helicity amplitude of the omega are extracted to be |F 1 | 2 = 0:3037 ± 0:0003 which does not agree with the expected value of a b 1 decay or results from a previous experiment. Future steps in all these analyses will be continued by a new graduate student in the group, culminating in a publication.

Foda, Ahmed↗
DOE OSTI2023

Measurement of spin-density matrix elements in ρ ( 770 ) production with a linearly polarized photon beam at E γ = 8.2 – 8.8 GeV

The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized 8.5GeV photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson rho(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. Here we confirm a high degree of s-channel helicity conservation at small squared four-momentum transfer t and are able to extract the t-dependence of natural and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full t range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced rho(770) differ by two units are negligible for -t<0.5GeV 2 /c 2 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2000

Coherence Measurements for Excited to Excited State Transitions in Barium

Experimental studies concerning elastic and inelastic electron scattering by coherently ensembles of Ba (...6s6p (sub 1)P(sub 1)) atoms with various degrees of alignment will be described. An in-plane, linearly-polarized laser beam was utilized to prepare these target ensembles and the electron scattering signal as a function of polarization angle was measured for several laser geometries at fixed impact energies and scattering angles. From these measurements, we derived cross sections and electron-impact coherence parameters associated with the electron scattering process which is time reverse of the actual experimentally studied process. This interpretation of the experiment is based on the theory of Macek and Herte. The experimental results were also interpreted in terms of cross sections and collision parameters associated with the actual experimental processes. Results obtained so far will be presented and plans for further studies will be discussed.

Trajmar, S.↗
DOE OSTI2023

Search for Isoscalar Resonances in yp ¿ wnp AT GLUEX

The GlueX experiment has produced the world?s largest statistics for peripheral photoproduction of mesons with a goal to search for exotic mesons. This document presents results on the search for possible intermediate resonances which decay to ??. Little is known for the states seen in this decay channel such as the ?(1420) and ?(1650). This channel also allows to search for the never seen exotics JPC = 0??, 2+?, and the elusive 2??. The ?, in this reaction, is identified via the ?+???0 decay mode and the ? and ?0 are identified via the decay to 2?. Data from the GlueX Phase I was analyzed. This data was obtained at the Thomas Jefferson National Accelerator Facility utilizing the GlueX detector and a tagged linearly polarized photon beam incident on a liquid hydrogen target. A model using the expected major wave contributors, 1+? and 1??, shows two structure in the region where the ?(1420) and ?(1650) are expected. A third structure is seen at threshold with the quantum numbers of an h1 resonance, however, more studies are needed to assert the nature of this structure. Instabilities on the m = ±1 were shown to come from mathematical ambiguities. This only occurs between the m = 1 and m = ?1 projections when both reflectivities are present in close amount. Expanding the intensity equation for a single wave allows to extract coefficients that can help describe the data. A tangent study is also presented in this document which consists on a direct fit to the lineshape of an isolated N(1535). This baryonic resonance is well established, but its Breit-Wigner parameters have only been obtained from partial wave analysis. In contrast, this study obtained the Breit-Wigner parameters using a direct fit and finds the value of the width to be 70.5± 9.2 MeV; this is half of the accepted value.

Barriga, Edmundo↗
DOE OSTI2024

First Measurement Using Elliptically Polarized Photons of the Double-Polarization Observable E for γ p → p π 0 and γ p → n π +

We report the measurement of the helicity asymmetry E for the p π 0 and n π + final states using, for the first time, an elliptically polarized photon beam in combination with a longitudinally polarized target at the Crystal Ball experiment at MAMI. The results agree very well with data that were taken with a circularly polarized photon beam, showing that it is possible to simultaneously measure polarization observables that require linearly (e.g., G ) and circularly polarized photons (e.g., E ) and a longitudinally polarized target. The new data cover a photon energy range 270–1400 MeV for the p π 0 final state (230–842 MeV for the n π + final state) and the full range of pion polar angles, θ , providing the most precise measurement of the observable E . A moment analysis gives a clear observation of the p η cusp in the p π 0 final state. Published by the American Physical Society 2024

Physics↗
DOE OSTI2024

Studies of e+e- Pair Photo-Production on Proton Target at 8 GeV in the GlueX Experiment

Lepton pair production has played an important role in both nuclear and particle physics, being among the earliest calculations utilizing QED, and seen most famously in the discovery of the J= at BNL. A technique is presented for measuring the linear polarization of GeV scale photon beams through the detection of e+e? pairs photo-produced in the target. This technique is applied to the analysis of GlueX data on proton target. Simulation predicts the analyzing power for pair production to be :5725 ? 0:0025 for the GlueX data, and the analysis of experimental data gives a linear polarization of approximately 35%, in good agreement with other measurements of beam polarization. The pair production technique is complementary to other electromagnetic and hadronic measurements of beam polarization, and is generally applicable in experiments that allow for forward angle electron and positron identi?fication and tracking. To facilitate this study, a neural net was trained for e=? separation to eliminate the pion background. Further, it is demonstrated that these e+e? pairs are sensitive to the proton charge form factor, which opens up the possibility for a new method to measure the proton RMS charge radius.

Schick, Andrew↗