89 research outputs found
Polarization of Tau Leptons Produced in Quasielastic Neutrino--Nucleon Scattering
A numerical analysis of the polarization vector of tau leptons produced
through quasielastic neutrino and antineutrino interactions with free nucleons
is given with two models for vector electromagnetic form factors of proton and
neutron. The impact of G parity violating axial and vector second-class
currents is investigated by applying a simple heuristic model for the induced
scalar and tensor form factors.Comment: Thesis of a talk given at the 8th Scientific Conference (SCYSS-04),
Dubna, Russia, 2 - 6 Feb 2004. 11 pages, 6 figures; added references, figures
and discussion; conclusions unchange
Deuteron Magnetic and Quadrupole Moments with a Poincar\'e Covariant Current Operator in the Front-Form Dynamics
The deuteron magnetic and quadrupole moments are unambiguosly determined
within the front-form Hamiltonian dynamics, by using a new current operator
which fulfills Poincar\'e, parity and time reversal covariance, together with
hermiticity and the continuity equation. For both quantities the usual
disagreement between theoretical and experimental results is largely removed.Comment: To appear in Phys. Rev. Let
New empirical fits to the proton electromagnetic form factors
Recent measurements of the ratio of the elastic electromagnetic form factors
of the proton, G_Ep/G_Mp, using the polarization transfer technique at
Jefferson Lab show that this ratio decreases dramatically with increasing Q^2,
in contradiction to previous measurements using the Rosenbluth separation
technique. Using this new high quality data as a constraint, we have reanalyzed
most of the world e-p elastic cross section data. In this paper, we present a
new empirical fit to the reanalyzed data for the proton elastic magnetic form
factor in the region 0 < Q^2 < 30 GeV^2. As well, we present an empirical fit
to the proton electromagnetic form factor ratio, G_Ep/G_Mp, which is valid in
the region 0.1 < Q^2 < 6 GeV^2
Poincare' Covariant Current Operator and Elastic Electron-Deuteron Scattering in the Front-form Hamiltonian Dynamics
The deuteron electromagnetic form factors, and , and the
tensor polarization , are unambiguously calculated within the
front-form relativistic Hamiltonian dynamics, by using a novel current, built
up from one-body terms, which fulfills Poincar\'e, parity and time reversal
covariance, together with Hermiticity and the continuity equation. A
simultaneous description of the experimental data for the three deuteron form
factors is achieved up to . At higher momentum transfer,
different nucleon-nucleon interactions strongly affect , , and
and the effects of the interactions can be related to -state
kinetic energy in the deuteron. Different nucleon form factor models have huge
effects on , smaller effects on and essentially none on
.Comment: 31 pages + 16 figures. Submitted to Phys. Rev.
Point-Form Analysis of Elastic Deuteron Form Factors
Point-form relativistic quantum mechanics is applied to elastic
electron-deuteron scattering. The deuteron is modeled using relativistic
interactions that are scattering-equivalent to the nonrelativistic Argonne
and Reid '93 interactions. A point-form spectator approximation (PFSA)
is introduced to define a conserved covariant current in terms of
single-nucleon form factors. The PFSA is shown to provide an accurate
description of data up to momentum transfers of 0.5 , but falls
below the data at higher momentum transfers. Results are sensitive to the
nucleon form factor parameterization chosen, particularly to the neutron
electric form factor.Comment: RevTex, 31 pages, 1 table, 13 figure
Neural Network Parameterizations of Electromagnetic Nucleon Form Factors
The electromagnetic nucleon form-factors data are studied with artificial
feed forward neural networks. As a result the unbiased model-independent
form-factor parametrizations are evaluated together with uncertainties. The
Bayesian approach for the neural networks is adapted for chi2 error-like
function and applied to the data analysis. The sequence of the feed forward
neural networks with one hidden layer of units is considered. The given neural
network represents a particular form-factor parametrization. The so-called
evidence (the measure of how much the data favor given statistical model) is
computed with the Bayesian framework and it is used to determine the best form
factor parametrization.Comment: The revised version is divided into 4 sections. The discussion of the
prior assumptions is added. The manuscript contains 4 new figures and 2 new
tables (32 pages, 15 figures, 2 tables
Nucleon Form Factors - A Jefferson Lab Perspective
The charge and magnetization distributions of the proton and neutron are
encoded in their elastic electromagnetic form factors, which can be measured in
elastic electron--nucleon scattering. By measuring the form factors, we probe
the spatial distribution of the proton charge and magnetization, providing the
most direct connection to the spatial distribution of quarks inside the proton.
For decades, the form factors were probed through measurements of unpolarized
elastic electron scattering, but by the 1980s, progress slowed dramatically due
to the intrinsic limitations of the unpolarized measurements. Early
measurements at several laboratories demonstrated the feasibility and power of
measurements using polarization degrees of freedom to probe the spatial
structure of the nucleon. A program of polarization measurements at Jefferson
Lab led to a renaissance in the field of study, and significant new insight
into the structure of matter.Comment: 20 pages, 9 figures; Chapter in the book "A decade of Physics at
Jefferson Lab", to be published in Journal of Physics: Conference Serie
Microscopic transition potential: Determination of and coupling constants
A transition potential, based on an effective
quark-quark interaction and a constituent quark cluster model for baryons, is
derived in the Born-Oppenheimer approach. The potential shows significant
differences with respect to those obtained by a direct scaling of the
nucleon-nucleon interaction. From its asymptotic behavior we extract the values
of and coupling constants in a
particular coupling schemeComment: 15 eps figures, Accepted for publication in Phys. Rev.
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