Electromagnetic Form Factors of the Proton in the "Unphysical" Region from gamma p->pe^{+}e^{-} Reaction

Investigation of the proton form factor F-1 (q(2), W-2) in the time-like region 4m(e)(2) <q(2) <4M(2) by measuring the e(+)e(-)-symmetry in the gamma(p,p)e(+)e(-) reaction is proposed. Selection of ''longitudinal'' photons (q(2

The 3^3He(e, e′'d)p Reaction in qω\omega-constant Kinematics

The cross section for the $^3$He(e, e$'$d)p reaction has been measured as a function of the missing momentum $p_m$ in q$\omega$ -constant kinematics at beam energies of 370 and 576 MeV for values of the three-momentum transfer $q$ of 412, 504 and 604 \mevc. The L(+TT), T and LT structure functions have been separated for $q$ = 412 and 504 \mevc. The data are compared to three-body Faddeev calculations, including meson-exchange currents (MEC), and to calculations based on a covariant diagrammatic expansion. The influence of final-state interactions and meson-exchange currents is discussed. The $p_m$-dependence of the data is reasonably well described by all calculations. However, the most advanced Faddeev calculations, which employ the AV18 nucleon-nucleon interaction and include MEC, overestimate the measured cross sections, especially the longitudinal part, and at the larger values of $q$. The diagrammatic approach gives a fair description of the cross section, but under(over)estimates the longitudinal (transverse) structure function.Comment: 17 pages, 7 figure

Relativistic Contributions to Deuteron Photodisintegration in the Bethe-Salpeter Formalism

In plane wave one-body approximation the reaction of deuteron photodisintegration is considered in the framework of the Bethe-Salpeter formalism for two-nucleon system. Results are obtained for deuteron vertex function, which is the solution of the homogeneous Bethe-Salpeter equation with a multi-rank separable interaction kernel, with a given analytical form. A comparison is presented with predictions of non-relativistic, quasipotential approaches and the equal time approximation. It is shown that important contributions come from the boost in the arguments of the initial state vertex function and the boost on the relative energy in the one-particle propagator due to recoil.Comment: 29 pages, 6 figure

Gauge constraints and electromagnetic properties of off-shell particles

The consequences of the gauge constraints for off-shellness in the electromagnetic (EM) vertices have been considered, using Compton scattering as an example. We have found that even if the gauge constraint for the 3-point EM Green function allows for off-shell effects in the charge (Dirac) form factor, they vanish in the total Compton scattering amplitude due to the gauge constraint for the 4-point EM Green function only. In addition, the representations of the Compton amplitude in terms of either reducible or irreducible vertices are equivalent for conserved currents.</p

Gauge constraints and electromagnetic properties of off-shell particles

The consequences of the gauge constraints for off-shellness in the electromagnetic (EM) vertices have been considered, using Compton scattering as an example. We have found that even if the gauge constraint for the 3-point EM Green function allows for off-shell effects in the charge (Dirac) form factor, they vanish in the total Compton scattering amplitude due to the gauge constraint for the 4-point EM Green function only. In addition, the representations of the Compton amplitude in terms of either reducible or irreducible vertices are equivalent for conserved currents

High missing-momentum components in 4He(e,e'p)3H reaction.

The cross section of the He-4(e, e''p)H-3 reaction has been measured for missing momenta 220 less than or equal to p(m) less than or equal to 690 MeV/c to study high-momentum components of the nuclear wave function and the reaction mechanism for this transition. The zero predicted in the plane-wave impulse approximation (PWIA) cross section, due to the underlying pt momentum distribution, is found to be washed out. Three types of calculations indicate that this is caused by final-state interactions and contributions from two-body currents. The calculations reproduce the high p(m) (600-690 MeV/c) data, although due to different ingredients in the models