Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “LEPTON REACTIONS”

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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Study of near-stability nuclei populated as fission fragments in heavy-ion fusion reactions

Examples are presented to illustrate the power of prompt {gamma}-ray spectroscopy of fission fragments from compound nuclei with A{approx}200 formed in fusion-evaporation reactions in experiments using the Gammasphere Ge-detector array. Complementary methods, such as Coulomb excitation and deep-inelastic processes, are also discussed. In other cases (n,xn{gamma}) reactions on stable isotopes have been used to establish neutron excitation functions for {gamma}-rays using a pulsed 'white'-neutron source, coupled to a high-energy-resolution germanium-detector array. The excitation functions can unambiguously assign {gamma}-rays to a specific reaction product. Results from all these methods bridge the gaps in the systematics of high-spin states between the neutron-deficient and neutron-rich nuclei. Results near shell closures should motivate new shell model calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

A N in inclusive lepton-proton collisions: TMD and twist-3 approaches

We consider the inclusive production of hadrons in lepton-nucleon scattering. For a transversely polarized nucleon this reaction shows a left-right azimuthal asymmetry, which we compute this asymmetry in both TMD and in twist-3 collinear factorization formalisms. All non-perturbative parton correlators of the calculation are fixed through information from other hard processes. Our results for the left-right asymmetry agree in sign with recent data for charged pion production from the HERMES Collaboration and from Jefferson Lab. As a result, we discuss similarities and differences of two formalisms.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

THE ROLE OF STOCHASTIC ACCELERATION IN THE PROMPT EMISSION OF GAMMA-RAY BURSTS: APPLICATION TO HADRONIC INJECTION

We study effects of particle re-acceleration (or heating) in the post-shock region via magnetohydrodynamic/plasma turbulence, in the context of a mixed hadronic-leptonic model for the prompt emission of gamma-ray bursts, using both analytical and numerical methods. We show that stochastically accelerated (or heated) leptons, which are injected via pp and p{gamma} reactions and subsequent pair cascades, are plausibly able to reproduce the Band function spectra with {alpha} {approx} 1 and {beta} {approx} 2-3 in the {approx}MeV range. An additional hard component coming from the proton-induced cascade emission is simultaneously expected, which can be compatible with observed extra power-law spectra far above the MeV range. We also discuss the specific implications of hadronic models for ongoing high-energy neutrino observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Left-right spin asymmetry in ℓ⁢ 𝑁 ↑ → ℎ⁡𝑋

We consider the inclusive production of hadrons in lepton-nucleon scattering. For a transversely polarized nucleon this reaction shows a left-right azimuthal asymmetry, which we compute in twist-3 collinear factorization at leading order in perturbation theory. All nonperturbative parton correlators of the calculation are fixed through information from other hard processes. Our results for the left-right asymmetry agree in sign with recent data for charged pion production from the HERMES Collaboration and from Jefferson Lab. However, the magnitude of the computed asymmetries tends to be larger than the data. Potential reasons for this outcome are identified. Furthermore, we also give predictions for future experiments and highlight in particular the unique opportunities at an electron ion collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

C HIMERA : A Massively Parallel Code for Core-collapse Supernova Simulations

Herein we provide a detailed description of the C HIMERA code, a code developed to model core collapse supernovae (CCSNe) in multiple spatial dimensions. The CCSN explosion mechanism remains the subject of intense research. Progress to date demonstrates that it involves a complex interplay of neutrino production, transport, and interaction in the stellar core, three-dimensional stellar core fluid dynamics and its associated instabilities, nuclear burning, and the fundamental physics of the neutrino–stellar core weak interactions and the equations of state of all stellar core constituents—particularly, the nuclear equation of state associated with core nucleons, both free and bound in nuclei. C HIMERA , by incorporating detailed neutrino transport, realistic neutrino–matter interactions, three-dimensional hydrodynamics, realistic nuclear, leptonic, and photonic equations of state, and a nuclear reaction network, along with other refinements, can be used to study the role of neutrino radiation, hydrodynamic instabilities, and a variety of input physics in the explosion mechanism itself. It can also be used to compute observables such as neutrino signatures, gravitational radiation, and the products of nucleosynthesis associated with CCSNe. The code contains modules for neutrino transport, multidimensional compressible hydrodynamics, nuclear reactions, a variety of neutrino interactions, equations of state, and modules to provide data for post-processing observables such as the products of nucleosynthesis, and gravitational radiation. C HIMERA is an evolving code, being updated periodically with improved input physics and numerical refinements. We detail here the current version of the code, from which future improvements will stem, which can in turn be described as needed in future publications.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Asymmetric relativistic Fermi gas model for quasielastic lepton-nucleus scattering

In this paper, we develop an asymmetric relativistic Fermi gas model for the study of the electroweak nuclear response in the quasielastic region. The model takes into account the differences between neutron and proton densities in asymmetric (N > Z) nuclei, as well as differences in the neutron and proton separation energies. We present numerical results for both neutral and charged-current processes, focusing on nuclei of interest for ongoing and future neutrino oscillation experiments. Finally, we point out some important differences with respect to the commonly employed symmetric Fermi gas model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Photoneutron cross sections for Au

Photoneutron cross sections were measured for Au in the entire energy range of the ({gamma},n) channel based on a direct neutron-counting technique with quasimonochromatic {gamma} rays produced in inverse Compton-scattering of laser photons with relativistic electrons. We present results of the measurement in comparison with the past data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Scrutinizing the evidence for N ( 1685 )

The helicity-dependent observable E for the reaction γd → ηn(p) with a spectator proton was recently measured in this paper by the A2 Collaboration at MAMI in Mainz. The data were interpreted as further evidence for a narrow resonance with spin and parity J P = 1/2 + (P 11 wave). However, a full partial-wave analysis without any narrow resonance leads to an excellent description of the data. Finally, imposing a narrow resonance with the properties suggested by the A2 Collaboration leads to a significant deterioration of the fit quality: there is no need for a narrow resonance.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Electron Screening in Metals

Electron screening enhances cross sections for nuclear reactions at low energies. We have studied the {sup 1}H({sup 7}Li,{alpha}){sup 4}He reaction in inverse kinematics and observed large electron screening only when the metallic targets were under tensile stress. Hydrogen was loaded into Pd and PdAg alloy foils from gas phase and concentrations reached about 0.6 protons per metallic atom. Mechanical pressure creates stress induced states in the metal. Without pressure hydrogen occupies octahedral interstitial positions in the fcc Pd lattice. Under stress some protons move to dislocated octahedral (dis-O) sites in the lattice. We believe that the magnitude of screening in various metals depends on the electron density on dis-O sites in case of fcc lattices or dislocated tetrahedral sites in bcc metals. We are currently trying to confirm the above by determining the electron density at the sites occupied by protons via the measurement of proton Knight's shift with {sup 1}H nuclear magnetic resonance technique.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Quasi-elastic Neutrino Scattering - an Overview

A non-technical overview of charge current quasi-elastic neutrino interaction is presented. Many body computations of multinucleon ejection which is proposed to explain recent large axial mass measurements are discussed. A few comments on recent experimental results reported at NuInt11 workshop are included.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Gallium vacancy complexes as a cause of Shockley-Read-Hall recombination in III-nitride light emitters

In this paper, we describe a mechanism by which complexes between gallium vacancies and oxygen and/or hydrogen act as efficient channels for nonradiative recombination in InGaN alloys. Our identification is based on first-principles calculations of defect formation energies, charge-state transition levels, and nonradiative capture coefficients for electrons and holes. The dependence of these quantities on alloy composition is analyzed. We find that modest concentrations of the proposed defect complexes (~10 16 cm -3 ) can give rise to Shockley-Read-Hall coefficients A = ( 10 7 - 10 9 ) s -1 . Finally, the resulting nonradiative recombination would significantly reduce the internal quantum efficiency of optoelectronic devices.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2012

Tau Lepton Flavor Violation Results from BaBar

We report the recent results obtained by BABAR collaboration in lepton flavor violation (LFV) searches in the tau lepton sector, presenting 16 new results from {tau}{sub LLL} (L = e, {mu}), {tau} {yields} LV{sup 0} V{sup 0} = {rho}{sup 0}, K*{sup 0}, K*{sup -0}, {Phi} and {tau} {yields} lK{sub S}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Fermilab E906/SeaQuest Drell-Yan Experiment

The E906/SeaQuest experiment will use the 120 GeV proton beam extracted from the Fermilab Main Injector to measure the Drell-Yan cross section in p-p, p-d, and p-A scattering. Data from liquid hydrogen and deuterium targets will be sensitive to the light anti-quark asymmetry, d-bar/u-bar, over a range of parton momentum fraction 0.04<x<0.45. Previous measurements from the E866/NuSea experiment have shown that while there were clear signs of flavor asymmetry at moderate x, the quark sea became flavor symmetric at higher x, suggesting a possible shift in the underlying mechanism generating the sea. Measurements from solid nuclear targets (carbon, calcium, and tungsten) will determine the modification of antiquark distributions in the nucleus. The results, in addition to being complementary to similar measurements performed through deep inelastic scattering, will also be valuable in providing the nuclear corrections necessary to extract nucleon parton distribution functions from neutrino data. The experiment will start in 2011, and will run for two years.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

A limit on the total lepton number in the Universe from BBN and the CMB

At temperatures below the QCD phase transition, any substantial lepton number in the Universe can only be present within the neutrino sector. In this work, we systematically explore the impact of a non-vanishing lepton number on Big Bang Nucleosynthesis (BBN) and the Cosmic Microwave Background (CMB). Relying on our recently developed framework based on momentum averaged quantum kinetic equations for the neutrino density matrix, we solve the full BBN reaction network to obtain the abundances of primordial elements. We find that the maximal primordial total lepton number L allowed by BBN and the CMB is -0.12 (-0.10) ≤ L ≤ 0.13 (0.12) for NH (IH), while specific flavor directions can be even more constrained. This bound is complementary to the limits obtained from avoiding baryon overproduction through sphaleron processes at the electroweak phase transition since, although numerically weaker, it applies at lower temperatures and is obtained completely independently. We publicly release the C++ code COFLASY-C on GitHub (https://github.com/mariofnavarro/COFLASY/tree/COFLASY-C) which solves for the evolution of the neutrino quantum kinetic equations numerically.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Reaction Dynamics And Nuclear Structure Via Deep Inelastic Collisions With Heavy-Ions: Search For Particle-Vibration Couplings in {sup 49}Ca

The deep inelastic reaction (DIC){sup 48}Ca+{sup 64}Ni, at an energy approximately 2.5 times above the Coulomb barrier, was studied using the CLARA-PRISMA setup at the Laboratori Nazionali di Legnaro. Total cross sections and angular distributions, both energy integrated and associated to the population of selected excited states, are measured for the most intense reaction channels. The {gamma}-decay of the most intense reaction products is also studied. The use of angular distributions and polarization measurements of {gamma} transitions allows to firmly establish spin and parity of excited states. Both reaction and gamma spectroscopy studies demonstrate the relevance of DIC with heavy ions for the investigation of moderately neutron rich systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Leptogenesis via hypermagnetic fields and baryon asymmetry

We study baryon asymmetry generation originated from the leptogenesis in the presence of hypermagnetic fields in the early Universe plasma before the electroweak phase transition (EWPT). For the simplest Chern-Simons (CS) wave configuration of hypermagnetic field we find the baryon asymmetry growth when the hypermagnetic field value changes due to α{sup 2}-dynamo and the lepton asymmetry rises due to the Abelian anomaly. We solve the corresponding integro-differential equations for the lepton asymmetries describing such self-consistent dynamics for lepto- and baryogenesis in the two scenarios: (i) when a primordial lepton asymmetry sits in right electrons e{sub R}; and (ii) when, in addition to e{sub R}, a left lepton asymmetry for e{sub L} and ν{sub eL} arises due to chirality flip reactions provided by inverse Higgs decays at the temperatures, T < T{sub RL} ∼ 10 TeV. We find that the baryon asymmetry of the Universe (BAU) rises very fast through such leptogenesis, especially, in strong hypermagnetic fields. Varying (decreasing) the CS wave number parameter k{sub 0} < 10{sup −7}T{sub EW} one can recover the observable value of BAU, η{sub B} ∼ 10{sup −9}, where k{sub 0} = 10{sup −7}T{sub EW} corresponds to the maximum value for CS wave number surviving ohmic dissipation of hypermagnetic field. In the scenario (ii) one predicts the essential difference of the lepton numbers of right- and left electrons at EWPT time, L{sub eR}−L{sub eL} ∼ (μ{sub eR}−μ{sub eL})/T{sub EW} = Δμ/T{sub EW} ≅ 10{sup −5} that can be used as an initial condition for chiral asymmetry after EWPT.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

A Search for a Close-Mass Lepton Doublet

Described is a search for a heavy charged lepton with an associated neutrino of nearly the same mass, together known as a close-mass lepton doublet. The search is conducted in e + e - annihilation data taken with the Mark II detector at a center-of- mass energy of 29 GeV. In order to suppress contamination from conventional two-photon reactions, the search applies a novel, radiative-tagging technique. Requiring the presence of an isolated, energetic photon allows exploration for lepton doublets with a mass splitting smaller than that previously accessible to experiment. No evidence for such a new lepton has been found, enabling limits to be placed on allowed mass combinations. Mass differences as low as 250-300 MeV are excluded for charged lepton masses up to 10 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗