54,236 research outputs found
Parton distributions for the pion in a chiral quark model
Parton distributions for the pion are studied in a chiral quark model
characterized by a quark propagator for which a spectral representation is
assumed. Electromagnetic and chiral symmetry constraints are imposed through
the relevant Ward-Takahashi identities for flavoured vertex functions.
Finiteness of the theory, requires the spectral function to be non-positive
definite. Straightforward calculation yields the result that the pion structure
function becomes one in the chiral limit, regardless of the details of the
spectral function. LO and NLO evolution provide a satisfactory description of
phenomenological parameterizations of the valence distribution functions but
fails to describe gluon and sea distributions.Comment: Latex, World Scientific, 8 pages, 1 figures. Talk given at the
Workshop on " Lepton Scattering, Hadrons and QCD " March 26 -- April 6, 2001.
Adelaide (Australia
Global superscaling analysis of quasielastic electron scattering with relativistic effective mass
We present a global analysis of the inclusive quasielastic electron
scattering data with a superscaling approach with relativistic effective mass.
The SuSAM* model exploits the approximation of factorization of the scaling
function out of the cross section under quasifree conditions. Our
approach is based on the relativistic mean field theory of nuclear matter where
a relativistic effective mass for the nucleon encodes the dynamics of nucleons
moving in presence of scalar and vector potentials. Both the scaling variable
and the single nucleon cross sections include the effective mass as a
parameter to be fitted to the data alongside the Fermi momentum . Several
methods to extract the scaling function and its uncertainty from the data are
proposed and compared. The model predictions for the quasielastic cross section
and the theoretical error bands are presented and discussed for nuclei along
the periodic table from to : H, H, He, He,
C, Li, Be, Mg, Ni,
Y, Sn, Ta, W, Au, O, Al,
Ca, Ca, Fe, Pb, and U.
We find that more than 9000 of the total data fall within the
quasielastic theoretical bands. Predictions for Ti and Ar are
also provided for the kinematics of interest to neutrino experiments.Comment: 26 pages, 20 figures and 4 table
- …