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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Pion Electgromagnetic Form Factor at High Q^2 from Lattice QCD

We show how momentum-space derivatives of hadron form factors can be related to their coordinate space moments computed in lattice QCD through a Fourier Transform. The method provides a priori information about the Q^2 dependence of form factors. As a specific application of the method, we obtain the slope of the isovector form factor of the nucleon at the various Q^2 accessible on the lattice, and hence derive the isovector charge radius. The method has potential application to the calculation of other form factors, including those relevant to hadronic weak decays.

Chakraborty, Dipasha↗
DOE OSTI2024

QED Meson Description of the Anomalous Particles at ∼17 and ∼38 MeV

The Schwinger confinement mechanism stipulates that a massless fermion and a massless antifermion are confined as a massive boson when they interact in the Abelian QED interaction in (1+1)D.If we approximate light quarks as massless and apply the Schwinger confinement mechanism to quarks, we can infer that a light quark and a light antiquark interacting in the Abelian QED interaction are confined as a QED meson in (1+1)D. Similarly, a light quark and a light antiquark interacting in the QCD interaction in the quasi-Abelian approximation will be confined as a QCD meson in (1+1)D. The QED and QCD mesons in (1+1)D can represent physical mesons in (3+1)D when the flux tube radius is properly taken into account. Such a theory leads to a reasonable description of the masses of π0,η, and η′, and its extrapolation to the unknown QED sector yields an isoscalar QED meson at about 17 MeV and an isovector QED meson at about 38 MeV. The observations of the anomalous soft photons, the hypothetical X17 particle, and the hypothetical E38 particle bear promising evidence for the possible existence of the QED mesons. Pending further confirmation, they hold important implications on the properties on the quarks and their interactions.

Wong, Cheuk-Yin (ORCID:0000000182230659)↗
DOE OSTI2013

Nucleon Form Factors with 2+1 Flavors of Domain Wall Fermions and All-Mode-Averaging

We report recent progress in the calculations of the isovector nucleon electromagnetic form factors using 2+1 flavors of domain wall fermions at pion masses of 170 MeV and 250 MeV. The lattice size is fixed at 323 ×64 with a lattice cutoff scale of 1.37(1) GeV. For the calculations with Mp = 170 MeV, we employed the All-Mode-Averaging (AMA) technique, which led to roughly a factor of 20 improvement in computational efficiency and has reduced the statistical errors in our results significantly. We were also able to do calculations at two different source-sink separations, at roughly 1.3 fm and 1.0 fm, without much additional cost by reusing the low eigenmodes stored for the AMA calculations. We will present results for the isovector form factors and their derived quantities, including the Dirac and Pauli radii, anomalous magnetic moment and discuss the effects of possible excited-state contaminations. Connected contributions to the isoscalar Dirac and Pauli form factors will also be shown.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Matrix elements from moments of correlation functions

Momentum-space derivatives of matrix elements can be related to their coordinate-space moments through the Fourier transform. We derive these expressions as a function of momentum transfer Q2 for asymptotic in/out states consisting of a single hadron. We calculate corrections to the finite volume moments by studying the spatial dependence of the lattice correlation functions. This method permits the computation of not only the values of matrix elements at momenta accessible on the lattice, but also the momentum-space derivatives, providing {\it a priori} information about the Q2 dependence of form factors. As a specific application we use the method, at a single lattice spacing and with unphysically heavy quarks, to directly obtain the slope of the isovector form factor at various Q2, whence the isovector charge radius. The method has potential application in the calculation of any hadronic matrix element with momentum transfer, including those relevant to hadronic weak decays.

Chang, Chia Cheng↗
DOE OSTI2011

Muon Capture on Light Nuclei

This work investigates the muon capture reactions 2H(\mu^-,\nu_\mu)nn and 3He(\mu^-,\nu_\mu)3H and the contribution to their total capture rates arising from the axial two-body currents obtained imposing the partially-conserved-axial-current (PCAC) hypothesis. The initial and final A=2 and 3 nuclear wave functions are obtained from the Argonne v_{18} two-nucleon potential, in combination with the Urbana IX three-nucleon potential in the case of A=3. The weak current consists of vector and axial components derived in chiral effective field theory. The low-energy constant entering the vector (axial) component is determined by reproducting the isovector combination of the trinucleon magnetic moment (Gamow-Teller matrix element of tritium beta-decay). The total capture rates are 393.1(8) s^{-1} for A=2 and 1488(9) s^{-1} for A=3, where the uncertainties arise from the adopted fitting procedure.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Giant dipole resonance parameters with uncertainties from photonuclear cross sections

Updated values and corresponding uncertainties of isovector giant dipole resonance (IVGDR or GDR) model parameters are presented that are obtained by the least-squares fitting of theoretical photoabsorption cross sections to experimental data. The theoretical photoabsorption cross section is taken as a sum of the components corresponding to excitation of the GDR and quasideuteron contribution to the experimental photoabsorption cross section. The present compilation covers experimental data as of January 2010. - Highlights: {yields} Experimental {sigma} ({gamma}, abs) or a sum of partial cross sections are taken as input to the fitting. {yields} Data include contributions from photoproton reactions. {yields} Standard (SLO) or modified (SMLO) Lorentzian approaches are used for formulating GDR models. {yields} Spherical or axially deformed nuclear shapes are used in GDR least-squares fit. {yields} Values and uncertainties of the SLO and SMLO GDR model parameters are tabulated.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Precision Study of Excited State Effects in Nucleon Matrix Elements

We present a dedicated precision analysis of the influence of excited states on the calculation of several nucleon matrix elements. This calculation is performed at fixed values of the lattice spacing, volume and pion mass that are typical of contemporary lattice computations. We focus on the nucleon axial charge, g{sub A}, for which we use 7,500 measurements, and on the average momentum of the unpolarized isovector parton distribution, x{sub u-d}, for which we use 23,000 measurements. All computations are done employing N{sub f}=2+1+1 maximally-twisted-mass Wilson fermions and non-perturbatively calculated renormalization factors. We find that excited state effects are negligible for g{sub A} and lead to a O(10%) downward shift for x{sub u-d}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

A high-accuracy extraction of the isoscalar {pi}N scattering length from pionic deuterium data

We present a high-accuracy calculation of the {pi}(bar sign)d scattering length using chiral perturbation theory up to order (M{sub {pi}/}m{sub p}){sup 7/2}. For the first time isospin-violating corrections are included consistently. The resulting value of a{sub {pi}-}bar{sub d} has a theoretical uncertainty of a few percent. We use it, together with data on pionic deuterium and pionic hydrogen atoms, to extract the isoscalar and isovector pion-nucleon scattering lengths from a combined analysis, and obtain a{sup +} (7.9{+-}3.2){center_dot}10{sup -3}M{sub {pi}}{sup -1} and a-bar (86.3{+-}1.0){center_dot}10{sup -3}M{sub {pi}}{sup -1}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Nucleon Structure from 2+1 Flavor Domain Wall QCD at Nearly Physical Pion Mass

The RBC and UKQCD collaborations have been investigating hadron physics in numerical lattice quantum chromodynamics (QCD) with (2+1) flavors of dynamical domain wall fermions (DWF) quarks that preserves continuum-like chiral and flavor symmetries. The strange quark mass is adjusted to physical value via reweighting and degenerate up and down quark masses are set as light as possible. In a recent study of nucleon structure we found a strong dependence on pion mass and lattice spatial extent in isovector axialvector-current form factors. This is likely the first credible evidence for the pion cloud surrounding nucleon. Here we report the status of nucleon structure calculations with a new (2+1)-flavor dynamical DWF ensembles with much lighter pion mass of 180 and 250 MeV and a much larger lattice spatial exent of 4.6 fm. A combination of the Iwasaki and dislocation-suppressing-determinant-ratio (I+DSDR) gauge action and DWF fermion action allows us to generate these ensembles at cutoff of about 1.4 GeV while keeping the residual breaking of chiral symmetry sufficiently small. Nucleon source Gaussian smearing has been optimized. Preliminary nucleon mass estimates are 0.98 and 1.05 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

On the nature of the Dipole Pygmy Resonance

The nature of the low-lying dipole states in neutron-rich nuclei, often associated to the Pygmy Dipole Resonance, has been investigated. This has been done by describing them within the Hartree-Fock plus RPA formalism. The analysis shows that they are not of collective nature although many particle-hole configurations participate to their formation. Taking advantage of their strong isospin mixing one can envisage combined reaction processes involving the Coulomb and different mixtures of isoscalar and isovector nuclear interactions in order to provide more hints to unveil the characteristic features of these states.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Lattice Calculations of Nucleon Form Factors

We present recent results of calculation of the isovector electromagnetic and axial form factors of the nucleon using lattice QCD with three different lattice actions and pion masses down to m{sub {pi}} > or approx. 300 MeV. Because of the precision of our high-statistics calculations, we can test predictions of baryon chiral perturbation theory for the charge and axial radii of the nucleon. We find that currently available baryon ChPT calculations disagree with our data, indicating that the corresponding effective theory approximations are not valid above m{sub {pi}{approx_equal}3}00 MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

The Charmonium-molecule hybrid structure of the X(3872)

We propose that the X(3872) has the charmonium and the DD*-bar hadronic molecule hybrid structure. We study the structure of the X(3872) using the schematic model with the separable interaction. The strengths of the couplings between the charmonium state and the hadronic molecule states are determined so as to reproduce the observed mass of the the X(3872). The isospin symmetry breaking is introduced by the mass differences of the neutral and charged D mesons. The obtained structure of the X(3872) is about 9% of cc-bar charmonium, 75% of the isoscalar DD*-bar molecule and 16percent; of the isovector DD*-bar molecule which explains observed properties of the X(3872) well.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Excited light meson spectroscopy from lattice QCD

I report on recent progress in calculating excited meson spectra using lattice QCD, emphasizing results and phenomenology. With novel techniques we can now extract extensive spectra of excited mesons with high statistical precision, including spin-four states and those with exotic quantum numbers. As well as isovector meson spectra, I will present new calculations of the spectrum of excited light isoscalar mesons, something that has up to now been a challenge for lattice QCD. I show determinations of the flavor content of these mesons, including the eta-eta' mixing angle, providing a window on annihilation dynamics in QCD. I will also discuss recent work on using lattice QCD to map out the energy-dependent phase shift in pi-pi scattering and future applications of the methodology to the study of resonances and decays.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Spin-Isospin responses via charge exchange reactions of RI beams at SHARAQ

Nuclear spectroscopy via direct reactions of RI beams is discussed focusing on characteristics of charge-exchange reactions of RI beams. Recent experiments using the SHARAQ spectrometer at the RIBF are presented, where isovector spin monopole and spin-non-flip monopole responses are studied by charge exchange reaction of RI beams. Some experimental plans and perspectives are also presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Role of momentum transfer in the quenching of the Gamow-Teller strength

A recent analysis of (p,n) and (n,p) reaction data from {sup 90}Zr was performed recently, where a significant amount of Gamow-Teller strength was found above the resonance, an energy region previously unreachable by experimental setups. The extracted strengths in the {beta}{sub -} and the {beta}{sub +} channel indicate that approximately 10% of the total strength necessary to satisfy the model independent Ikeda sum rule is missing. One possible source of this discrepancy is the treatment of the isovector spin monopole (IVSM) mode of excitation which has been found to occurr at high excitation energies. Employing the relativistic Hartree-Bogoliubov (RHB) model and the protonneutron relativistic quasiparticle random phase approximation (pn-RQRPA) to calculate the nuclear response, we explore the contribution of the IVSM mode to the total L= 0 strength and apply our results to the available data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Density-dependent covariant energy density functionals

Relativistic nuclear energy density functionals are applied to the description of a variety of nuclear structure phenomena at and away fromstability line. Isoscalar monopole, isovector dipole and isoscalar quadrupole giant resonances are calculated using fully self-consistent relativistic quasiparticle randomphase approximation, based on the relativistic Hartree-Bogoliubovmodel. The impact of pairing correlations on the fission barriers in heavy and superheavy nuclei is examined. The role of pion in constructing desnity functionals is also investigated.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Renormalization of the Brazilian chiral nucleon-nucleon potential

In this work we present a renormalization of the Brazilian nucleon-nucleon (NN) potential using a subtractive method. We show that the exchange of correlated two pion is important for isovector channels, mainly in tensor and central potentials.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗