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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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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Nucleon resonance structure studies via exclusive KY electroproduction

Studying the structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings of $N^*$ states in the mass range below 1.8~GeV have been determined from analyses of CLAS $\pi N$, $\eta N$, and $\pi \pi N$ data. This work has made it clear that consistent results from independent analyses of several exclusive channels with different couplings and non-resonant backgrounds but the same $N^*$ electro excitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic coupling, many high-lying $N^*$ states preferentially decay through the $\pi \pi N$ channel instead of $\pi N$. Data from the $KY$ channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying $N^*$ states against those determined from the $\pi N$ and $\pi \pi N$ channels. Lastly, a program to study excited $N^*$ state structure in both non-strange and strange exclusive electroproduction channels using CLAS12 will measure differential cross sections and polarization observables to be used as input to extract the $\gamma_vNN^*$ electrocoupling amplitudes for the most prominent $N^*$ states in the range of invariant energy $W$ up 3~GeV in the virtually unexplored domain of momentum transfers $Q^2$ up to 12~GeV$^2$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Excited nucleon spectrum and structure studies with CLAS and CLAS12

The study of the spectrum and structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The CLAS detector in Hall B has provided the dominant part of the available world data on most relevant meson electroproduction channels off the nucleon in the resonance region for Q2 up to 5 GeV2. Analyses of CLAS data for the exclusive channels πN, ηN, and π+π-p on a proton target have provided the only results available on the Q2 evolution of the electro-excitation amplitudes for the transitions from the initial photon-proton to the final N* states in the mass range up to W =1.8 GeV. These electrocouplings allow for exploration of the internal structure of the produced excited nucleon states. This work has made it clear that consistent results from independent analyses of several exclusive channels with different resonance hadronic decay parameters and non-resonant backgrounds but the same N* electro-excitation amplitudes, is essential to have confidence in the extracted results. Starting in early 2018, a program to study the spectrum and structure of N* states in various exclusive electroproduction channels using the new CLAS12 spectrometer commenced. These studies will probe the structure of N* states in the mass range up to W =3 GeV and for Q2 as low as 0.05 GeV2 and as high as 10-12 GeV2, thus providing a means to access N* structure information spanning a broad range of distance scales. Quasi-real photoproduction studies are also planned to search for additional N* states, the so-called hybrid baryons, for which the glue serves as an active structural component. In this talk the N* programs from both CLAS and CLAS12 will be reviewed.

Carman, D. S.↗
DOE OSTI2013

γvNN^* Transition Amplitudes and Excited Baryon Structure from CLAS

Studying excited nucleon structure through exclusive-meson electroproduction reactions is key for understanding the nature of the strong interaction in the non-perturbative regime. With its nearly complete coverage of the final-state phase space, the CLAS detector at JLab has provided the lion's share of the world's meson-electroproduction data for differential cross sections and the asymmetries arising from single- and double-polarization observables. Electrocouplings for most of the excited nucleon states (N*) in mass range of up to 1.8~GeV have been determined from several analyses of the CLAS data for photon virtualities (Q2) up to 5.0 GeV2 for the pi+n, pi0p, and eta p channels [1,3] as well as for the pi+pi-p reaction for Q2<1.5~GeV2 [2,3]. Physics analyses of these N* electrocouplings [2,3] have revealed that the structure of excited nucleon is formed of an internal core of dressed quarks with an external meson-baryon cloud. Our N*-electrocoupling results afford access to the non-perturbative strong interaction responsible for generating the different N* states and will also provide testing ground for the inspired by QCD quark model predictions. A dedicated experiment will run after the 12 GeV upgrade to JLab on the extraction of the N* electrocouplings in the yet unexplored region of high photon virtualities ranging from 5.0 to 12 GeV2. The anticipated results are of particular importance in providing a understanding of the nature of confinement and dynamical chiral symmetry breaking in baryons based upon the QCD [3].\\[4pt] [1] I.G. Aznauryan and V.D. Burkert, Prog. Part. Nucl. Phys. \textbf{67}, 1 (2012).\\[0pt] [2] V.I. Mokeev \textit{et~al.} (CLAS Collaboration), Phys. Rev. \textbf{C86}, 035203 (2012).\\[0pt] [3] I.G. Aznauryan \textit{et~al.}, ``Studies of Nucleon Resonance Structure in Exclusive Meson Electroproduction,'' arXiv:1212.4891[nucl-th].

Mokeev, Victor↗
DOE OSTI2015

Excited Baryon Structure Using Exclusive Reactions with CLAS12

Studying excited nucleon structure through exclusive electroproduction reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. Electrocouplings for $N^*$ states in the mass range below 1.8~GeV have been determined from analyses of CLAS $\pi N$, $\eta N$, and $\pi \pi N$ data. This work made it clear that consistency of independent analyses of exclusive channels with different couplings and non-resonant backgrounds but the same $N^*$ electro-excitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic coupling, many high-lying $N^*$ states preferentially decay through the $\pi \pi N$ channel instead of $\pi N$. Data from the $KY$ channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying $N^*$ states against those determined from the $\pi N$ and $\pi \pi N$ channels. A program to study excited $N^*$ decays to non-strange and strange exclusive final states using CLAS12 will measure differential cross sections to be used as input to extract the $\gamma_vNN^*$ transition form factors for the most prominent $N^*$ states in the range of invariant energy $W$ up 3~GeV in the virtually unexplored domain of momentum transfers $Q^2$ up to 12~GeV$^2$.

Carman, Daniel↗
DOE OSTI2014

Central Exclusive Production at the Tevatron

The Collider Detector at Fermilab, CDF, observed for the first time in hadron-hadron collisions photon-photon (gamma + gamma -> e+e-, mu+mu-) and photon-pomeron (gamma + \BbbP -> J/psi, psi(2S)) interactions, as well as $p+\bar{p}\rightarrow p+\chi_c+\bar{p}$ by double pomeron exchange, \BbbP + \BbbP or DPE. Exclusive pi+pi- production was also measured at $\sqrt{s} = 900~{\rm GeV}$ and 1960 GeV; resonance structures are discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Exclusive dimuon production in ultraperipheral Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV with ATLAS

Exclusive dimuon production in ultraperipheral collisions (UPC), resulting from photon-photon interactions in the strong electromagnetic fields of colliding high-energy lead nuclei, PbPb(γγ) → μ + μ - (Pb (*) Pb (*) ), is studied using $\mathcal{L}$ int = 0.48 nb -1 of $\sqrt{s_{NN}}$ = 5.02 TeV lead-lead collision data at the LHC with the ATLAS detector. Dimuon pairs are measured in the fiducial region p T,μ >4 GeV, |η μ |<2.4, invariant mass m μμ >10 GeV, and p T,μμ <2 GeV. The primary background from single-dissociative processes is extracted from the data using a template fitting technique. Differential cross sections are presented as a function of m μμ , absolute pair rapidity (|y μμ |), scattering angle in the dimuon rest frame (| cos $\mathscr{O}$$^{*}_{μμ}$|), and the colliding photon energies. The total cross section of the UPC γγ → μ + μ - process in the fiducial volume is measured to be $σ^{μμ}_{fid}$ = 34.1 ± 0.3(stat.) ± 0.7(syst.) μb. Generally good agreement is found with calculations from STARlight, which incorporate the leading-order Breit-Wheeler process with no final-state effects, albeit differences between the measurements and theoretical expectations are observed. In particular, the measured cross sections at larger |y μμ | are found to be about 10–20% larger in data than in the calculations, suggesting the presence of larger fluxes of photons in the initial state. Modification of the dimuon cross sections in the presence of forward and/or backward neutron production is also studied and is found to be associated with a harder incoming photon spectrum, consistent with expectations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Propagation of Cryogenic Thermal Fractures from Unconfined PMMA Boreholes

In cryogenic fracturing, a rock surface exposed to cryogenic fluids undergoes a large thermal gradient, and the resultant local tensile stress overcomes rock strength and initiates fractures. This study investigates the development of cracks generated from the cryogenic treatment of a borehole under no external confining stress on specimens. The experiments were performed on transparent PMMA specimens to observe fracture proliferation around boreholes. Liquid nitrogen was flowed through the boreholes to cool the borehole surface. The results show that initial fracture growth is characterized by abrupt starts and stops, and as the fracture propagates outward, the growth appears more continuous. In an early stage, horizontal/radial fractures and vertical fractures are the defining patterns. Horizontal fractures tend to be separated by a specific exclusion distance (i.e., spacing between cracks). While distinct horizontal/vertical fractures and exclusion distance manifest themselves at an early stage, fractures resulting from fracture interactions and curvatures can develop into complex shapes at later stages. Cryogenic thermal loading induces distinctively curved fractures. The tendency of curvature may prevent greater penetration. An increase in the borehole pressure during liquid nitrogen flow, however, can lessen fracture tortuosity and facilitate radial propagation. A high flow pressure and rate are also advantageous in that they accelerate cooling and fracture propagation.

42 ENGINEERING↗
DOE OSTI2018

CLAS N* Excitation Results from Pion and Kaon Electroproduction

The study of the structure of excited nucleon $N^*$ states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings of $N^*$ states in the mass range below $W$=1.8~GeV have been determined from analyses of CLAS $\pi N$, $\eta N$, and $\pi \pi N$ data at four-momentum transfers $Q^2$ up to 5~GeV$^2$. The work has made it clear that consistent results from independent analyses of several exclusive channels with different couplings and non-resonant backgrounds but the same $N^*$ electroexcitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic couplings, many high-lying $N^*$ states preferentially decay through the $\pi \pi N$ channel, while couplings to $\pi N$ final states become rather small. The resonance parameters determined from $\pi N$ and $\pi \pi N$ electroproduction can be checked in independent studies of the $KY$ ($Y = \Lambda, \Sigma^0$) channels. Therefore, data from the $KY$ channels already measured with CLAS will play an important role in $N^*$ structure studies. These comparisons await the development of suitable reaction models. Starting in 2018, a program to study the structure of $N^*$ states in various exclusive electroproduction channels using the new CLAS12 spectrometer will get underway. These studies will probe the structure of $N^*$ states in the mass range up to $W$=3~GeV and $Q^2$ up to 12~GeV$^2$, thus providing a means to access $N^*$ structure information spanning a broad regime encompassing both low- and high-energy degrees of freedom.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

CLAS N* Excitation Results from Pion and Kaon Electroproduction

The study of the structure of excited nucleon $N^*$ states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings of $N^*$ states in the mass range below $W$=1.8~GeV have been determined from analyses of CLAS $\pi N$, $\eta N$, and $\pi \pi N$ data at four-momentum transfers $Q^2$ up to 5~GeV$^2$. The work has made it clear that consistent results from independent analyses of several exclusive channels with different couplings and non-resonant backgrounds but the same $N^*$ electroexcitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic couplings, many high-lying $N^*$ states preferentially decay through the $\pi \pi N$ channel, while couplings to $\pi N$ final states become rather small. The resonance parameters determined from $\pi N$ and $\pi \pi N$ electroproduction can be checked in independent studies of the $KY$ ($Y = \Lambda, \Sigma^0$) channels. Therefore, data from the $KY$ channels already measured with CLAS will play an important role in $N^*$ structure studies. These comparisons await the development of suitable reaction models. Starting in 2018, a program to study the structure of $N^*$ states in various exclusive electroproduction channels using the new CLAS12 spectrometer will get underway. These studies will probe the structure of $N^*$ states in the mass range up to $W$=3~GeV and $Q^2$ up to 12~GeV$^2$, thus providing a means to access $N^*$ structure information spanning a broad regime encompassing both low- and high-energy degrees of freedom.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Searching for neutrino self-interactions at future muon colliders

Multi-TeV muon colliders offer a powerful means of accessing new physics coupled to muons while generating clean and intense high-energy neutrino beams via muon decays. We study a fixed-target experiment leveraging the neutrino beams and a forward detector pointing at the interaction point of the muon collider. The sensitivity to neutrino self-interactions is analyzed as a feasibility study, focusing on the leptonic scalar ϕ exclusively coupled to the Standard Model neutrinos. Our work shows that projections from both the main and forward detectors can enhance the existing limits by two orders of magnitude, surpassing other future experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Predicting the critical gradient of ITG turbulence in fusion plasmas

The quasilinear mixing-length approach to efficient prediction of transport in fusion devices is improved to account for the ‘Dimits’ upshift between linear and nonlinear critical pressure gradients in zonal-flow-saturated turbulence regimes. This modification uses the frequency mismatch between modes interacting turbulently to track changes in saturation efficiency. Near criticality, energy is transferred exclusively to stable eigenmodes, rapidly increasing the efficacy of the nonlinearity. Finally, the modified quasilinear model is able to predict below-threshold turbulent ion-temperature-gradient-driven transport accurately and also yields significantly improved predictions for trapped-electron-mode transport.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Structure of a novel antibacterial toxin that exploits elongation factor Tu to cleave specific transfer RNAs

Contact-dependent growth inhibition (CDI) is a mechanism of inter-cellular competition in which Gram-negative bacteria exchange polymorphic toxins using type V secretion systems. Here, we present structures of the CDI toxin from Escherichia coli NC101 in ternary complex with its cognate immunity protein and elongation factor Tu (EF-Tu). The toxin binds exclusively to domain 2 of EF-Tu, partially overlapping the site that interacts with the 3'-end of aminoacyl-tRNA (aa-tRNA). The toxin exerts a unique ribonuclease activity that cleaves the single-stranded 3'-end from tRNAs that contain guanine discriminator nucleotides. EF-Tu is required to support this tRNase activity in vitro , suggesting the toxin specifically cleaves substrate in the context of GTP·EF-Tu·aa-tRNA complexes. However, superimposition of the toxin domain onto previously solved GTP·EF-Tu·aa-tRNA structures reveals potential steric clashes with both aa-tRNA and the switch I region of EF-Tu. Further, the toxin induces conformational changes in EF-Tu, displacing a β-hairpin loop that forms a critical salt-bridge contact with the 3'-terminal adenylate of aa-tRNA. Altogether, these observations suggest that the toxin remodels GTP·EF-Tu·aa-tRNA complexes to free the 3'-end of aa-tRNA for entry into the nuclease active site.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Search for new phenomena in final states with an energetic jet and large missing transverse momentum in p p collisions at s = 13 TeV using the ATLAS detector

We report results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum. The search uses proton-proton collision data corresponding to an integrated luminosity of 3.2 fb $-$1 at $\sqrt{s}$ = 13 TeV collected in 2015 with the ATLAS detector at the Large Hadron Collider. Events are required to have at least one jet with a transverse momentum above 250 GeV and no leptons. Several signal regions are considered with increasing missing-transverse-momentum requirements between E$miss\atop{T}$ > 250 GeV and E$miss\atop{T}$ > 700 GeV . Good agreement is observed between the number of events in data and Standard Model predictions. The results are translated into exclusion limits in models with large extra spatial dimensions, pair production of weakly interacting dark-matter candidates, and the production of supersymmetric particles in several compressed scenarios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

A SIMPLE Bubble Chamber for Dark Matter Searches: Testing and Development

SIMPLE (Superheated Instrument for Massive Particle Experiments) is one of only three experiments worldwide in search of evidence of astroparticle dark matter (WIMPs) using halocarbon-loaded superheated liquid (SHL) detectors. The 2012 Phase II SIMPLE measurements yielded the most restrictive exclusion contour in the spin-dependent (SD) sector of WIMP-proton interactions from a direct search experiment at the time, overlapping for the first time results previously obtained only indirectly [1]. In order to remain competitive with other experiments in the field, the next phase measurement requires larger exposure over shorter observation times with significantly improved neutron shielding. To increase exposure, SIMPLE plans, as a first step, to replace its superheated droplet detectors (SDDs), each containing an active mass of about 15 g of halocarbon, with bubble chambers capable of holding up to 20 kg of active halocarbon mass. We report on the development of the first 1 kg halocarbon SIMPLE bubble chamber prototype, including chamber recompression system design and testing and initial acoustic detection of bubble formation. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Quasielastic lepton scattering and back-to-back nucleons in the short-time approximation

Understanding quasielastic electron- and neutrino-scattering from nuclei has taken on new urgency with current and planned neutrino oscillation experiments, and with electron scattering experiments measuring specific final states, such as those involving nucleon pairs in “back-to-back” configurations. Accurate many-body methods are available for calculating the response of light (A ≤ 12) nuclei to electromagnetic and weak probes, but they are computationally intensive and only applicable to the inclusive response. In the present work we introduce a novel approach, based on realistic models of nuclear interactions and currents, to evaluate the short-time (high-energy) inclusive and exclusive response of nuclei. The approach accounts reliably for crucial two-nucleon dynamics, including correlations and currents, and provides information on back-to-back nucleons observed in electron and neutrino scattering experiments. We demonstrate that in the quasielastic regime and at moderate momentum transfers both initial- and final-state correlations, and two-nucleon currents are important for a quantitatively successful description of the inclusive response and final state nucleons. Finally, the approach can be extended to include relativistic—kinematical and dynamical—effects, at least approximately in the two-nucleon sector, and to describe the response in the resonance-excitation region.

6 ≤ A ≤ 19↗
DOE OSTI2024

Dark SRF, a cavity-based search for the Dark Photon: new exclusion limit and path forward

The dark photon is a hypothesized particle in extension to the Standard Model (SM) that would weakly interact with ordinary SM photons. An effective way to search for hidden sector photons in a laboratory set up is through light-shining-through-wall (LSW) schemes.We present here the first results of Dark SRF, a LSW experiment that leverages ultra-high quality factor superconducting radio frequency (SRF) cavities to search for dark photons. The use of Nb SRF cavities combined with a strict calibration and measurement protocol increased sensitivity to dark photons by several orders of magnitude compared to other LSW experiments, as demonstrated by our new exclusion limit on the dark photon mixing angle.In addition to the results of the search conducted in liquid helium using 1.3GHz SRF cavities, we also present the first steps of the second phase of the experiment, which will take place in a dilution refrigerator using 2.6GHz SRF cavities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Structural insight into the dual function of LbpB in mediating Neisserial pathogenesis

Lactoferrin-binding protein B (LbpB) is a lipoprotein present on the surface of Neisseria that has been postulated to serve dual functions during pathogenesis in both iron acquisition from lactoferrin (Lf), and in providing protection against the cationic antimicrobial peptide lactoferricin (Lfcn). While previous studies support a dual role for LbpB, exactly how these ligands interact with LbpB has remained unknown. Here, we present the structures of LbpB from N. meningitidis and N. gonorrhoeae in complex with human holo-Lf, forming a 1:1 complex and confirmed by size-exclusion chromatography small-angle X-ray scattering. LbpB consists of N- and C-lobes with the N-lobe interacting extensively with the C-lobe of Lf. Our structures provide insight into LbpB’s preference towards holo-Lf, and our mutagenesis and binding studies show that Lf and Lfcn bind independently. Our studies provide the molecular details for how LbpB serves to capture and preserve Lf in an iron-bound state for delivery to the membrane transporter LbpA for iron piracy, and as an antimicrobial peptide sink to evade host immune defenses.

59 BASIC BIOLOGICAL SCIENCES↗