450 research outputs found
Analysis of excited quark propagator effects on neutron charge form factor
The charge form factor and charge radius of neutron are investigated in the
perturbative chiral quark model (PCQM) with considering both the ground and
excited states in the quark propagator. A Cornell-like potential is extracted
in accordance with the predetermined ground state quark wavefunction, and the
excited quark states are derived by solving the Dirac equation with the
extracted PCQM potential numerically. The study reveals that the contributions
of the excited quark states are considerably influential in the charge form
factor and charge radius of neutron as expected, and the total results are
significantly improved and increased by nearly four times by including the
excited states in the quark propagator. The theoretical PCQM results are found,
including the ground and excited quark propagators, in good agreement with the
recent lattice QCD values at pion mass of about 130 MeV.Comment: 8 pages, 8 figure
Study of and structures via transitions
The helicity amplitudes of the and resonances in the
electromagnetic transition are studied in the constituent
quark model using the impulse approximation, with the proton and resonances
assumed to be in three-quark configurations. The comparison of theoretical
results and experimental data on the helicity amplitudes , ,
and indicates that the and resonances are
primarily composed of three-quark states but may contain additional
components. However, it is improbable that contributions from meson clouds will
be dominant at low .Comment: 6 pages, 3 figure
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