739 research outputs found
The nucleon to Delta electromagnetic transition form factors in lattice QCD
The electromagnetic nucleon to Delta transition form factors are evaluated
using two degenerate flavors of dynamical Wilson fermions and using dynamical
sea staggered fermions with domain wall valence quarks. The two subdominant
quadrupole form factors are evaluated for the first time in full QCD to
sufficient accuracy to exclude a zero value, which is taken as a signal for
deformation in the nucleon-Delta system. For the Coulomb quadrupole form factor
the unquenched results show deviations from the quenched results at low q^2
bringing dynamical lattice results closer to experiment, thereby confirming the
importance of pion cloud contributions on this quantity.Comment: 15 pages, 8 Figure
Axial Nucleon to Delta transition form factors on 2+1 flavor hybrid lattices
We correct the values of the dominant nucleon to Delta axial transition form
factors CA_5 and CA_6 published in C. Alexandrou et.al., Phys. Rev. D 76,094511
(2007). The analysis error affects only the values obtained when using the
hybrid action in the low Q^2 regime bringing them into agreement with those
obtained with Wilson fermions.Comment: 1+2 pages, 2 figures, 1 Table, Erratum to C. Alexandrou et.al., Phys.
Rev. D 76, 094511 (2007
Heavy-light baryonic mass splittings from the lattice
We present lattice estimates of the mass of the heavy-light baryons
and obtained using propagating heavy quarks. For
our result is GeV, after
extrapolation to the continuum limit and in the quenched approximation.Comment: 3 pages postscript, Contribution to Lattice'9
Evaluation and Verification of Bottom Acoustic Reverberation Statistics Predicted by the Point Scattering Model
The point scatteringmodel offers a parameterization of the reverberation probability density function (pdf) in terms of the coefficient of excess (kurtosis) and a coherent component represented by a harmonic process with random phase. In this paper the potential utility of this parametrization is investigated in the context of seafloor characterization. The problem of separating out the effect of each parameter is discussed. Computer simulations are used to verify model predictions on the reverberation quadrature, envelope, and phase pdf. As part of the verification study, the scatterer density was determined from the kurtosis of the reverberation quadrature pdf. A statistical analysis of this procedure points to reduced estimate accuracy with decreasing kurtosis. Additional computer simulations show that the chosen pdf family, developed under the assumption of a Poissonscatterer distribution, is flexible enough to fit reverberation data generated by non‐Poisson scatterer distributions exhibiting a degree of clustering or regularity. A computer experiment demonstrates how this parametrization can be used in conjunction with a simple sonar geometry to generate acoustic signatures for seafloor classification. In addition, real reverberation data collected by a Sea Beam sonar system in two different seafloor areas are interpreted according to the chosen parametrization
The electromagnetic form factors of the Omega in lattice QCD
We present results on the Omega baryon electromagnetic form factors using
domain-wall fermion configurations for three pion masses in the range
of about 350 to 300 MeV. We compare results obtained using domain wall fermions
with those of a mixed-action (hybrid) approach, which combine domain wall
valence quarks on staggered sea quarks, for a pion mass of about 350 MeV. We
pay particular attention in the evaluation of the subdominant electric
quadrupole form factor to sufficient accuracy to exclude a zero value, by
constructing a sequential source that isolates it from the dominant form
factors. The magnetic moment, , the electric
charge and magnetic radius, , are extracted for
these pion masses. The electric quadrupole moment is determined for the first
time using dynamical quarks.Comment: 13 pages, 10 Figure
Calculation of fermion loops for and nucleon scalar and electromagnetic form factors
The exact evaluation of the disconnected diagram contributions to the
flavor-singlet pseudoscalar meson mass, the nucleon sigma term and the nucleon
electromagnetic form factors, is carried out utilizing GPGPU technology with
the NVIDIA CUDA platform. The disconnected loops are also computed using
stochastic methods with several noise reduction techniques. Various dilution
schemes as well as the truncated solver method are studied. We make a
comparison of these stochastic techniques to the exact results and show that
the number of noise vectors depends on the operator insertion in the fermionic
loop.Comment: Version accepted for publication in Comp. Phys. Commun. References
added. 13 pages, 12 figure
Nucleon to Delta transition form factors with domain wall fermions
We calculate the electromagnetic, axial and pseudo-scalar form factors of the
Nucleon to transition using two dynamical light degenerate
quarks and a dynamical strange quark simulated with the domain wall fermion
action. Results are obtained at lattice spacings fm and
fm, with corresponding pion masses of MeV and MeV, respectively.
High statistics measurements are achieved by utilizing the coherent sink
technique. The dominant electromagnetic dipole form factor, the axial form
factors and the pseudo-scalar coupling are extracted to a good accuracy. This
allows the investigation of the non-diagonal Goldberger-Treiman relation.
Particular emphasis is given on the extraction of the sub-dominant
electromagnetic quadrupole form factors and their ratio to the dominant dipole
form factor, and , measured in experiment.Comment: 31 pages, 10 figure
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