Electroproduction of ρ~0 mesons on protons in quasielastic kinematics at intermediate energies and spin-flip mechanism of direct meson knockout

摘要

It is shown that the amplitude for the direct knockout of ρ~0 mesons plays an important role at energies W above the resonance region, W ? 2 GeV, and rather high values of Q~2 ? 1.5-2 GeV~2/c~2 and that it corresponds to the t pole in the channel of the virtual decay p → p + π~0 accompanied by quark-spin flip upon momentum transfer to the meson, π~0 + γ*_T → ρ~0. The contributions of several scalar mesons (p → p + f_0 channel), the contribution of the tensor meson f_2, and effects of the interference between different contributions were taken into account in addition to the contribution of the π~0 meson. The vectorand tensor-meson-dominance models were used to estimate the respective vertex constants. Within the proposed mechanism, the differential cross sections dσ_L/dt and dσ_T/dt were calculated for several W and Q~2 values at which the respective total cross sections were measured by the CLAS Collaboration. Agreement with data on the transverse part of the total cross section, σ_T, was attained, whereby the assumption of a dominant role of magnetic spin transitions in the meson skin of the nucleon under conditions of quasielastic-knockout kinematics is confirmed. At the same time, the contribution of spin-flip transitions is suppressed in the longitudinal part of the cross section, σ_L, and this is confirmed by the results of our calculations. The behavior of the differential cross section dσ_T/dt is predicted with an eye to future experiments.