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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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2D temperature field reconstruction using optimized Gaussian radial basis function networks
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Silicon carbide detectors for high flux neutron monitoring at near-core locations
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Event reconstruction in a liquid xenon Time Projection Chamber with an optically-open field cage
nEXO is a proposed tonne-scale neutrinoless double beta decay (0νββ) experiment using liquid 136 Xe (LXe) in a Time Projection Chamber (TPC) to read out ionization and scintillation signals. Between the field cage and the LXe vessel, a layer of LXe (“skin” LXe) is present, where no ionization signal is collected. Only scintillation photons are detected, owing to the lack of optical barrier around the field cage. Here, in this work, we show that the light originating in the skin LXe region can be used to improve background discrimination by 5% over previous published estimates. This improvement comes from two elements. First, a fraction of the γ-ray background is removed by identifying light from interactions with an energy deposition in the skin LXe. Then, background from 222 Rn dissolved in the skin LXe can be efficiently rejected by tagging the α decay in the 214 Bi- 214 Po chain in the skin LXe.
An integrated online radioassay data storage and analytics tool for nEXO
Large-scale low-background detectors are increasingly used in rare-event searches as experimental collaborations push for enhanced sensitivity. However, building such detectors, in practice, creates an abundance of radioassay data especially during the conceptual phase of an experiment when hundreds of materials are screened for radiopurity. A tool is needed to manage and make use of the radioassay screening data to quantitatively assess detector design options. We have developed a Materials Database Application for the nEXO experiment to serve this purpose. Furthermore, this paper describes this database application, explains how it functions, and discusses how it streamlines the design of the experiment.
Ultra-sensitive radon assay using an electrostatic chamber in a recirculating system
Rare event searches such as neutrinoless double beta decay and Weakly Interacting Massive Particle detection require ultra-low background detectors. Radon contamination is a significant challenge for these experiments, which employ highly sensitive radon assay techniques to identify and select low-emission materials. This work presents the development of ultra-sensitive electrostatic chamber (ESC) instruments designed to measure radon emanation in a recirculating gas loop, for future lower background experiments. Unlike traditional methods that separate emanation and detection steps, this system allows continuous radon transport and detection. This is made possible with a custom-built recirculation pump. A Python-based analysis framework, PyDAn, was developed to process and fit time-dependent radon decay data. Radon emanation rates are given for various materials measured with this instrument. A radon source of known activity provides an absolute calibration, enabling statistically-limited minimal detectable activities of 20 µBq. These devices are powerful tools for screening materials in the development of low-background particle physics experiments.
Design of a high voltage delivery system for noble liquid time projection chambers
Noble liquid time projection chambers (TPCs) are a leading technology in the detection of ionizing radiation, particularly in applications such as accelerator neutrino physics, dark matter detection, and neutrinoless double beta decay. This work addresses the design considerations for implementing stable high voltage (HV) systems within large noble liquid TPCs, with a focus on the nEXO experiment. Utilizing insights from prior HV research and experimental investigations, we outline factors influencing HV stability and discuss design choices to improve stability and prevent electrical discharges. A novel HV delivery system concept is presented, tailored for the nEXO TPC, which incorporates these design considerations while also meeting the stringent radiopurity requirements of the nEXO neutrinoless double beta decay search. These design considerations and their specific implementation towards a HV delivery system offer guidance to future experiments applying high voltage in noble liquid environments.
Study of e + e – → D + D – π + π – at center-of-mass energies from 4.36 to 4.60 GeV
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Measurement of the absolute branching fraction of Λ c + → p K S 0 η decays
Based on 586 pb -1 of e + e - annihilation data collected at a center-of-mass energy of √s = 4.6 GeV with the BESIII detector at the BEPCII collider, the absolute branching fraction of $Λ^+_c$ → $pK^0_Sη$ decays is measured for the first time to be $B$($Λ^+_c$ → $pK^0_Sη$) = (0.414±0.084±0.028)%, where the first uncertainty is statistical and the second is systematic. The result is compatible with a previous CLEO result on the relative branching fraction B ( Λ c + → p K S 0 η ) B ( Λ c + → p K − π + ) , and consistent with theoretical predictions of SU(3) flavor symmetry.
Measurement of proton electromagnetic form factors in the time-like region using initial state radiation at BESIII
The electromagnetic process e + e - → $p\bar{p}$ is studied with the initial-state-radiation technique using 7.5 fb -1 of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/c 2 using the $p\bar{p}$ invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.
Search for an axion-like particle in radiative $J/ψ$ decays
We search for an axion-like particle (ALP) a through the process $\psi$(3686) → π + π – J/$\psi$, J/$\psi$ → γa, a → γγ in a data sample of (2.71 ± 0.01) x 10 9 $\psi$(3686) events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay J/$\psi$ → γa and the ALP-photon coupling constant g aγγ are set at 95% confidence level in the mass range of 0.165 ≤ m a ≤ 2.84 GeV/c 2 . The limits on $\mathscr{B}$(J/$\psi$ → γa) range from 8.3 x 10 –8 to 1.8 x 10 –6 over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for 0.165 ≤ m a ≤ 1.468 GeV/c 2 .
Search for invisible decays of a dark photon using e + e – annihilation data at BESIII
We report a search for a dark photon using 14.9 fb –1 of e + e – annihilation data taken at center-of-mass energies from 4.13 to 4.60 GeV with the BESIII detector operated at the BEPCII storage ring. The dark photon is assumed to be produced in the radiative annihilation process of e + e – and to predominantly decay into light dark matter particles, which escape from the detector undetected. The mass range from 1.5 to 2.9 GeV is scanned for the dark photon candidate, and no significant signal is observed. The mass dependent upper limits at the 90% confidence level on the coupling strength parameter ϵ for a dark photon coupling with an ordinary photon vary between 1.6 x 10 –3 and 5.7 x 10 –3 .
Search for the semi-leptonic decays Λ c + → Λ π + π - e + ν e and Λ c + → p K S 0 π - e + ν e
We search for the semi-leptonic decays $Λ^+_c$ → Λπ + π - e + ν e and $Λ^+_c$ → p$K^0_S$π - e + ν e in a sample of 4.5 fb -1 of e + e - annihilation data collected in the center-of-mass energy region between 4.600 GeV and 4.699 GeV by the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be B($Λ^+_c$ → Λπ + π - e + ν e ) < 3.9 × 10 -4 and B($Λ^+_c$ → p$K^0_S$π - e + ν e ) < 3.3 × 10 -4 at the 90% confidence level, respectively
Search for a massless particle beyond the Standard Model in the Σ+ → p + invisible decay
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Structure of the Human Respiratory Syncytial Virus M2-1 Protein in Complex with a Short Positive-Sen
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Localized High Concentration Electrolytes for High Voltage Lithium-Metal Batteries: Correlation between the Electrolyte Composition and Its Reductive/Oxidative Stability
We demonstrate a first-principles screening methodology as an effective tool to explore electrolyte formulations for the new generation of high energy density rechargeable batteries. We study the liquid structure and electronic properties in dilute electrolytes, high concentration electrolytes (HCE), and localized high concentration electrolytes (LHCE), with focus on electrolyte formulations based on lithium bis(fluorosulfonyl)imide (LiFSI), dimethyl carbonate (DMC), and bis(2,2,2-trifluoroethyl) ether (BTFE) as a diluent. We describe the solvation complexes in the dilute electrolyte and explore structural changes triggered by the increase in lithium salt concentration for HCEs and the diluent effects in LHCEs. In HCE formulations, there is a 4-fold coordination environment of lithium-ions as in the dilute electrolyte, but the number of lithium-ion interactions with O atoms from FSI- anions dominates. In these solutions, the ability of the FSI- anions to interact with multiple lithium-ions allows complex 3D network formation and influences the reductive/oxidative behavior of the electrolyte. Interestingly, in LHCEs, the BTFE diluent molecules do not change the 3D solution structure when diluting the HCE formulation from 5.49 to 3.83 M. However, there is a composition threshold where the structural and electronic behavior may change. We show that diluting the HCE electrolyte with BTFE down to 1.77 M breaks the three-dimensional solution structure into an island-like solvation complex. We relate these structural changes to the electronic properties of the electrolytes finding a causal relationship between the reductive/oxidative behavior and the lithium-oxygen interaction mechanisms in the solvated complexes. The coordination with lithium-ions lowers the electrolyte LUMO and HOMO levels: the higher is the number of interactions with lithium-ions, the more likely the solvent molecule, FSI- anion, or diluent molecule is to be reduced and the less likely it is to become oxidized. The evolution of the solvated ion structure in HCE and LHCE suggests a close connection to a corresponding change in the lithium-ion transport mechanisms for these electrolytes.