43,031 research outputs found
Meson Resonances at large Nc: Complex Poles vs Breit-Wigner Masses
The rigorous quantum mechanical definition of a resonance requires
determining the pole position in the second Riemann sheet of the analytically
continued partial wave scattering amplitude in the complex Mandelstam
s-variable plane. For meson resonances we investigate the alternative
Breit-Wigner (BW) definition within the large Nc expansion. By assuming that
the pole position is and exploiting unitarity, we show
that the BW determination of the resonance mass differs from the pole position
by terms, which can be extracted from pi-pi scattering
data. For the case of the f0(600) pole, the BW scalar mass is predicted to
occur at about 700 MeV while the true value is located at about 800 MeV.Comment: 7 pages. No figures. (elsevier preprint
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
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