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Register a new userNuclear effects in leptoproduction of secondaries
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We estimate the energy losses in the case of deep-inelastic scattering on nuclear targets in terms of the effective change of the virtual photon energy. Our phenomenological results are in reasonable agreement with theoretical calculations. The difference in secondary production processes in hard and soft interactions is discussed.
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We analyze the light meson leptoproduction within the handbag approach. We show that effects determined by the transversity Generalized Parton Distributions (GPDs), $H_T$ and $bar E_T$ are essential in the description of pseudoscalar and vector meson leptoproduction.
Leptoproduction of nucleons into the backward hemisphere on nuclear targets is studied at relativistic subasymptotic energies and momenta. The relativistic internucleon potential is extracted from appropriate photoproduction data. Different production mechanisms are found to work together and interfere. Whenever rescattering is kinematically possible, it gives the bulk of the contribution, except at very high Q^2. Comparison with the existing data at E=2.4 GeV shows a reasonable agreement.
We study the perturbative and parametric stability of the QCD predictions for the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ and azimuthal $cos(2varphi)$ asymmetry, $A(x,Q^2)$, in heavy-quark leptoproduction. We review the available theoretical results for these quantities and conclude that, contrary to the production cross sections, the ratios $R(x,Q^2)$ and $A(x,Q^2)$ are stable under radiative QCD corrections in wide region of the variables $x$ and $Q^2$. This implies that large radiative contributions to the structure functions cancel each other in the ratios $R(x,Q^2)$ and $A(x,Q^2)$ with good accuracy. Then we consider some experimental and phenomenological applications of the observed perturbative stability. We provide compact analytic predictions for $R(x,Q^2)$ and azimuthal $cos(2varphi)$ asymmetry in the case of low $xll 1$. It is demonstrated that our obtained results will be useful in the extraction of the structure functions from measurements of the reduced cross sections. Finally, we analyze the properties of $R(x,Q^2)$ and $A(x,Q^2)$ within the variable-flavor-number scheme (VFNS) of QCD. We conclude that the Callan-Gross ratio and azimuthal asymmetry are perturbatively stable but sensitive to resummation of the mass logarithms of the type $alpha_{s}lnleft( Q^{2}/m^{2}right)$. For this reason, the quantities $R(x,Q^2)$ and $A(x,Q^2)$ will be good probes of the heavy-quark content of the proton.
Absorptive corrections, known to suppress proton-neutron transitions with large fractional momentum $zto1$ in pp collisions, become dramatically strong on a nuclear target, and push the partial cross sections of leading neutron production to the very periphery of the nucleus. The mechanism of $pi$-$a_1$ interference, which successfully explains the observed single-spin asymmetry in polarized $ppto nX$, is extended to collisions of polarized protons with nuclei. Corrected for nuclear effects, it explains the observed single-spin azimuthal asymmetry of neutrons, produced in inelastic events, where the nucleus violently breaks up. The single-spin asymmetry is found to be negative and nearly $A$-independent.
We investigate the gluonic structure of nuclei within a mean-field model of nuclear structure based upon the self-consistent modification of the structure of a bound nucleon, with the nucleon described by the Nambu--Jona-Lasinio model. This approach has been shown to reproduce the European Muon Collaboration (EMC) effect, involving the ratio of the spin-independent structure functions of a heavier nucleus to that of the deuteron. It also predicts a significant nuclear modification for the spin structure functions, known as the polarized EMC effect. Here we report sizeable nuclear modifications of the gluon distributions (a gluon EMC effect) for the ratios of both the unpolarized and polarized gluon distributions in nuclear matter to those of a free nucleon.
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