arXiv subjects
Publications and source records attributed to N. Bianchi.
We discuss the quark transversity distribution function and a possible way to access it through the measurement of single spin azimuthal asymmetry in semi-inclusive single pion electroproduction on a transversely polarized target.
The azimuthal single target-spin asymmetries for pi^{+} production in semi-inclusive deep inelastic scattering of leptons off longitudinally polarized protons are evaluated using two main approaches available in the literature. It is shown that the approximation where the twist-2 transverse quark spin distribution in the longitudinally polarized nucleon is small enough to be neglected leads to a consistent description of all existing asymmetries observed by the HERMES experiment.
We consider the sin(phi) single target-spin asymmetry in deep-inelastic pi^{+} inclusive electroproduction off a longitudinally polarized target. We show that at larger transverse momentum of the outgoing hadron the evaluated asymmetry decreases if one takes into account the first order alpha_S perturbative contribution to the cross section, integrated over the azimuthal angle. This leads to good agreement with recent HERMES data.
A model based on the hadronic fluctuations of the real photon is developed to describe the total photonucleon and photonuclear cross sections in the energy region above the nucleon resonances. The hadronic spectral function of the photon is derived including the finite width of vector-meson resonances and the quark-antiquark continuum. The shadowing effect is evaluated considering the effective interaction of the hadronic component with the bound nucleons within a Glauber-Gribov multiple scattering theory. The low energy onset of the shadowing effect is interpreted as a possible signature of a modification of the hadronic spectral function in the nuclear medium. A decrease of the $ρ$-meson mass in nuclei is suggested for a better explanation of the experimental data.
The energy and nuclear mass dependences of the total hadronic cross section in the energy range 0.5-2.6 GeV have been measured at Bonn using the SAPHIR tagged photon beam. The measurement, performed on C, Al, Cu, Sn and Pb, provides the first photoabsorption data in the region 1.2-1.7 GeV. The results show a significant reduction of the photoabsorption strength on the bound nucleon compared to the free nucleon case in the whole energy region. Above 1.2 GeV this reduction decreases with the nuclear density and can be interpreted as a signature of a low energy onset of the shadowing effect.
The forward Compton scattering amplitude for carbon and lead have been calculated from total photoabsorption cross section data by using dispersion relations. The results show a large difference between the scattering amplitudes for nuclei and the free nucleon, above the $Δ$ region. The forward Compton scattering cross sections have been calculated and compared with the available data. The Weise sum rule is discussed together with the prediction of a recent theoretical model.
We investigate the $sin ϕ$ azimuthal asymmetry in the semi-inclusive deep-inelastic lepton scattering off longitudinally polarized nucleon target arising from the time reversal odd structures. The order 1/Q contributions of the leading twist and twist-three distribution and fragmentation functions to that asymmetry for the certain kinematical conditions are numerically estimated.
We consider the azimuthal asymmetries in semi-inclusive deep inelastic leptoproduction arising due to both perturbative and nonperturbative effects at HERMES energies and show that the $k_T^2/Q^2$ order corrections to $< \cosϕ>$ and $< \cos2ϕ>$ are significant. We also reconsider the results of perturbative effects for $< \cosϕ>$ at large momentum transfers \cite{A1} using the more recent sets of scale-dependent distribution and fragmentation functions, which bring up to $18{%}$ difference in $< \cosϕ>$. In the same approach we calculate the $< \cos2ϕ>$ as well.
The results of an experiment on inclusive electron scattering from an oxygen jet target, performed in a wide range of energy and momentum transfer covering both quasi-elastic and $Δ$(1232) resonance regions, are reported. In the former region the theoretical predictions, obtained including effects of nucleon-nucleon correlations in both initial and final states, give a good description of the experimental data. In the inelastic region a broadening as well as a damping of the resonant part of the cross section with respect to the free nucleon case is observed. The need of more detailed calculations including nuclear structure effects on the electroproduction cross section of nucleon resonances is highlighted.