Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “GeV”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

NuSTAR OBSERVATIONS OF GRB 130427A ESTABLISH A SINGLE COMPONENT SYNCHROTRON AFTERGLOW ORIGIN FOR THE LATE OPTICAL TO MULTI-GEV EMISSION

GRB 130427A occurred in a relatively nearby galaxy; its prompt emission had the largest GRB fluence ever recorded. The afterglow of GRB 130427A was bright enough for the Nuclear Spectroscopic Telescope ARray (NuSTAR) to observe it in the 3-79 keV energy range long after its prompt emission (∼1.5 and 5 days). This range, where afterglow observations were previously not possible, bridges an important spectral gap. Combined with Swift, Fermi, and ground-based optical data, NuSTAR observations unambiguously establish a single afterglow spectral component from optical to multi-GeV energies a day after the event, which is almost certainly synchrotron radiation. Such an origin of the late-time Fermi/Large Area Telescope >10 GeV photons requires revisions in our understanding of collisionless relativistic shock physics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Fermi Galactic Center GeV excess and implications for dark matter

Here, the region around the Galactic Center (GC) is now well established to be brighter at energies of a few GeV than what is expected from conventional models of diffuse gamma-ray emission and catalogs of known gamma-ray sources. We study the GeV excess using 6.5 yr of data from the Fermi Large Area Telescope. We characterize the uncertainty of the GC excess spectrum and morphology due to uncertainties in cosmic-ray source distributions and propagation, uncertainties in the distribution of interstellar gas in the Milky Way, and uncertainties due to a potential contribution from the Fermi bubbles. We also evaluate uncertainties in the excess properties due to resolved point sources of gamma rays. The GC is of particular interest, as it would be expected to have the brightest signal from annihilation of weakly interacting massive dark matter (DM) particles. However, control regions along the Galactic plane, where a DM signal is not expected, show excesses of similar amplitude relative to the local background. Furthermore, based on the magnitude of the systematic uncertainties, we conservatively report upper limits for the annihilation cross-section as a function of particle mass and annihilation channel.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Heavy ion collisions from $\sqrt{s_{NN}}$ of 62.4 GeV down to 7.7 GeV in the EPOS4 framework

The EPOS4 project is an attempt to construct a realistic model for describing relativistic collisions of different systems, from proton-proton (𝑝⁢𝑝) to nucleus-nucleus (𝐴⁢𝐴), at energies from several TeV per nucleon down to several GeV. We argue that a parallel scattering formalism (as in EPOS4) is relevant for primary scatterings in 𝐴⁢𝐴 collisions above 4 GeV, whereas sequential scattering (cascade) is appropriate below. We present briefly the basic elements of EPOS4, and then investigate heavy ion collisions from 62.4 GeV down to 7.7 GeV, to understand how physics changes with energy, studying in particular the disappearance of the fluid component at low energies.

Monte Carlo methods↗
DOE OSTI2016

Participant and spectator scaling of spectator fragments in Au + Au and Cu + Cu collisions at s N N = 19.6 and 22.4 GeV

Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to nitrogen (Z = 7), are measured in PHOBOS. These fragments are observed in Au+Au ( s N N = 19.6 GeV) and Cu+Cu (22.4 GeV) collisions at high pseudorapidity (η). The dominant multiply-charged fragment is the tightly bound helium (α), with lithium, beryllium, and boron all clearly seen as a function of collision centrality and pseudorapidity. In this paper, we observe that in Cu+Cu collisions, it becomes much more favorable for the α fragments to be released than lithium. The yields of fragments approximately scale with the number of spectator nucleons, independent of the colliding ion. The shapes of the pseudorapidity distributions of fragments indicate that the average deflection of the fragments away from the beam direction increases for more central collisions. Finally, a detailed comparison of the shapes for α and lithium fragments indicates that the centrality dependence of the deflections favors a scaling with the number of participants in the collision.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Cross sections of 𝜂 mesons in 𝑝 +𝑝 collisions at forward rapidity at $\sqrt{𝑠}$ = 500 GeV and central rapidity at $\sqrt{𝑠}$ = 510 GeV

We present the first measurements of the forward and midrapidity 𝜂-meson cross sections from 𝑝 + 𝑝 collisions at $\sqrt{𝑠}$ = 500 and 510 GeV, respectively. We also report the midrapidity 𝜂/𝜋 0 ratio at 510 GeV. The forward cross section is measured differentially in 𝜂-meson transverse momentum (𝑝 𝑇 ) from 1.0 to 6.5 GeV/𝑐 for pseudorapidity 3.0 < |𝜂| < 3.8. The midrapidity cross section is measured from 3.5 to 44 GeV/𝑐 for pseudorapidity |𝜂| < 0.35. Both cross sections serve as critical inputs to an updated global analysis of the 𝜂-meson fragmentation functions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1973

Hodoscope Measurements of the Spectrum of Cosmic Electrons Between 10 Gev and 100 Gev

In an attempt to reduce divergences among independent measurements of the electron spectrum above 10 GeV, electrons were detected with the aid of a large hodoscope which incorporates 8 trays of Geiger tubes and 10 scintillation counters into a calorimeter containing 33 radiation lengths of lead. This instrument was thoroughly calibrated up to 9 GeV with an electron synchrotron and was flown twice at a depth of 5 g/sq cm for a total of 30 hours at ceiling. Electron showers at 10 GeV are completely contained within the calorimeter where their ionization is sampled twelve times, and where hodoscope trays provide information on the geometrical distribution of shower particles. Electrons appeared in a histogram of number of events vs. a X2 measure of goodness of fit to electron shower curves as a clearly resolved peak standing well above the nuclear background. The initial ionization and the lateral spread of shower particles are consistent with those of calibration electrons. In contrast, the behavior of the nuclear continuum associated with minimum ionizing incident particles is different from that of calibration electrons but similar to that of nuclear events associated with incident helium nuclei. The differential electron spectrum from 10 to 100 GeV was obtained.

Meegan, C. A.↗
DOE OSTI2014

Right-handed neutrino production rate at T>160 GeV

The production rate of right-handed neutrinos from a Standard Model plasma at a temperature above a hundred GeV has previously been evaluated up to NLO in Standard Model couplings (g∼2/3) in relativistic (M∼πT) and non-relativistic regimes (M≫πT), and up to LO in an ultrarelativistic regime (M≲gT). The last result necessitates an all-orders resummation of the loop expansion, accounting for multiple soft scatterings of the nearly light-like particles participating in 1↔2 reactions. In this paper we suggest how the regimes can be interpolated into a result applicable for any right-handed neutrino mass and at all temperatures above 160 GeV. The results can also be used for determining the lepton number washout rate in models containing right-handed neutrinos. Numerical results are given in a tabulated form permitting for their incorporation into leptogenesis codes. We note that due to effects from soft Higgs bosons there is a narrow intermediate regime around M∼g{sup 1/2}T in which our interpolation is phenomenological and a more precise study would be welcome.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Exclusive π 0 p electroproduction off protons in the resonance region at photon virtualities 0.4 GeV 2 ≤ Q 2 ≤ 1 GeV 2

The limited electroproduction process e p → e ' p ' π 0 was measured in the range of photon virtualities Q 2 = 0.4 – 1.0 GeV 2 and the invariant mass range of the p π 0 system of W = 1.1 – 1.8 GeV. These kinematics are covered in exclusive π 0 electroproduction off the proton with nearly complete angular coverage in the p π 0 center-of-mass system and with high statistical accuracy. Nearly 36 000 cross-section points were measured, and the structure functions σ T + ε σ L , σ L T , and σ T T , were extracted via fitting the φ π 0 dependence of the cross section. A Legendre polynomial expansion analysis demonstrates the sensitivity of our data to high-lying N * and Δ * resonances with M > 1.6 GeV. As part of a broad effort to determine the electrocouplings of the N * and Δ * resonances using both single- and double-pion electroproduction, this dataset is key for the reliable extraction of the high-lying resonance electrocouplings from the combined isospin analysis of the N π and π + π - p channels.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Event structure and double helicity asymmetry in jet production from polarized p+p collisions at (sq rt) s = 200 GeV

We report on the event structure and double helicity asymmetry (A{sub LL}) of jet production in longitudinally polarized p+p collisions at {radical}s = 200 GeV. Photons and charged particles were measured by the PHENIX experiment at midrapidity |{eta}| < 0.35 with the requirement of a high-momentum (> 2 GeV/c) photon in the event. Event structure, such as multiplicity, p{sub T} density and thrust in the PHENIX acceptance, were measured and compared with the results from the pythia event generator and the geant detector simulation. The shape of jets and the underlying event were well reproduced at this collision energy. For the measurement of jet ALL, photons and charged particles were clustered with a seed-cone algorithm to obtain the cluster p{sub T} sum (p{sub T}{sup reco}). The effect of detector response and the underlying events on p{sub T}{sup reco} was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the next-to-leading-order and perturbative quantum chromodynamics jet production cross section. For 4 < p{sub T}{sup reco} < 12 GeV/c with an average beam polarization of <P> = 49% we measured A{sub LL} = -0.0014 {+-} 0.0037{sup stat} at the lowest p{sub T}{sup reco} bin (4-5 GeV/c) and -0.0181 {+-} 0.0282{sup stat} at the highest p{sub T}{sup reco} bin (10-12 GeV/c) with a beam polarization scale error of 9.4% and a p{sub T} scale error of 10%. Jets in the measured p{sub T}{sup reco} range arise primarily from hard-scattered gluons with momentum fraction 0.02 < x < 0.3 according to pythia. The measured A{sub LL} is compared with predictions that assume various {Delta}G(x) distributions based on the Gluck-Reya-Stratmann-Vogelsang parameterization. The present result imposes the limit -1.1 < {integral}{sub 0.02}{sup 0.3}dx{Delta}G(x,{mu}{sup 2} = 1 GeV{sup 2}) < 0.4 at 95% confidence level or {integral}{sub 0.02}{sup 0.3}dx{Delta}G(x,{mu}2 = 1 GeV{sup 2}) < 0.5 at 99% confidence level.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Measurements of Multiparticle Correlations in d + Au Collisions at 200, 62.4, 39, and 19.6 GeV and p + Au Collisions at 200 GeV and Implications for Collective Behavior

Recently, multiparticle-correlation measurements of relativistic p/d/ 3 He + Au, p + Pb, and even p + p collisions show surprising collective signatures. In this paper, we present beam-energy-scan measurements of two-, four-, and six-particle angular correlations in d + Au collisions at √ s NN = 200, 62.4, 39, and 19.6 GeV. We also present measurements of two- and four-particle angular correlations in p + Au collisions at √ s NN = 200 GeV. We find the four-particle cumulant to be real valued for d + Au collisions at all four energies. We also find that the four-particle cumulant in p + Au has the opposite sign as that in d + Au. Further, we find that the six-particle cumulant agrees with the four-particle cumulant in d + Au collisions at 200 GeV, indicating that nonflow effects are subdominant. Finally, these observations provide strong evidence that the correlations originate from the initial geometric configuration, which is then translated into the momentum distribution for all particles, commonly referred to as collectivity.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Petawatt Laser Guiding and Electron Beam Acceleration to 8 GeV in a Laser-Heated Capillary Discharge Waveguide.

Guiding of relativistically intense laser pulses with peak power of 0.85 PW over 15 diffraction lengths was demonstrated by increasing the focusing strength of a capillary discharge waveguide using laser inverse bremsstrahlung heating. This allowed for the production of electron beams with quasimonoenergetic peaks up to 7.8 GeV, double the energy that was previously demonstrated. Charge was 5 pC at 7.8 GeV and up to 62 pC in 6 GeV peaks, and typical beam divergence was 0.2 mrad.

Gonsalves, AJ↗
DOE OSTI2014

TMDs and PVDIS: JLab 6 GeV results and 12 GeV Plan

The talk shows recent and new results with a transversely polarized 3He(n) to explore TMDs with 6 GeV JLab, including Collins/Sivers/Worm-gear asymmetries on pions and Kaons, inclusive hadron and electron SSA. Then presents JLab-12GeV plan for TMD study - high precision Multi-d mapping, with focusing on the SoLID program on TMDs. The talk also shows new results of PVDIS with 6 GeV JLab, which were just published in Nature. Then discussed the 12 GeV plan for PVDIS, the SoLID program on PVDIS.

Chen, Jian-Ping↗
NASA NTRS1971

Balloon measurements of the energy spectrum of cosmic electrons between 1 GeV and 25 GeV

During three balloon flights made in 1966 and 1967, cosmic electrons were investigated with the aid of a hodoscope detector which provided extensive and detailed information on each cosmic ray event triggering the apparatus. Similar information obtained during calibration exposures to protons and pions as well as to electrons was used to provide identification of cosmic electrons and to determine their energies. Differential primary electron intensities measured in the range from 1 GeV to 25 GeV were substantially larger than some earlier measurements. Taken in conjunction with existing measurements at energies above 100 GeV, this indicates that the energy spectrum of cosmic electrons is steeper than that of cosmic-ray nuclei and, consequently, suggests that Compton/synchrotron energy loss plays a significant role in shaping the electron spectrum.

Earl, J. A.↗
DOE OSTI2014

Higgs portal vector dark matter for GeV scale γ-ray excess from galactic center

We show that the GeV scale γ-ray excess from the direction of the Galactic Center can be naturally explained by the pair annihilation of Abelian vector dark matter (VDM) into a pair of dark Higgs bosons (VV→ϕϕ), followed by the subsequent decay of ϕ into bb{sup -bar} or ττ{sup -bar}. All the processes are described by a renormalizable VDM model with the Higgs portal, which is naturally flavor-dependent. Some parameter space of this scenario can be tested at the near future direct dark matter search experiments such as LUX and XENON1T.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗