arXiv subjects
Publications and source records attributed to N. N. Nikolaev.
We derive a generalized Balitskii-Fadin-Kuraev-Lipatov equation, which applies directly to the perturbative QCD component of total cross section. With the gluon correlation radius $R_{c} \sim 0.4$f we reproduce the empirical rate of growth of the hadron-nucleon total cross sections. The simultaneous estimate of the triple-pomeron coupling also agrees with the experiment.
Misprints and numerical coefficients corrected, a bit of phenomenology and one figure added. The case for the linear evolution of the unitarized structure functions made stronger.
The 1993 witnessed two major news in the field of color transparency (CT): i) no effect of CT was seen in the SLAC NE18 experiment on $A(e,e'p)$ scattering at virtualities of the exchanged photon $Q^{2} \lsim 7$ GeV$^{2}$, ii) strong signal of CT was observed in the Fermilab E665 experiment on exclusive $ρ^{0}$-meson production in deep inelastic scattering in the same range of $Q^{2}$. Both are good news and rule in CT, since this striking difference in the onset of CT for two reactions was predicted theoretically, and we review the theory of both reactions and the origin of this difference. We discuss an importance of final state interaction effects for the theoretical interpretation of the NE18 data. We comment on possible CT effects in the $^{4}He(e,e'p)$ interactions at CEBAF.
The exclusive production of vector mesons in deep inelastic scattering is a hard scattering process with the well controlled size of quark configurations which dominate the production amplitude. This allows an unambiguous prediction of color transparency effects in the coherent and incoherent production of vector mesons on nuclei. We demonstrate how the very mechanism of color transparency leads to a belated onset of color transparency effects as a function of $Q^{2}$. We conclude that the $Q^{2}$ dependence of the exclusive $ρ^{0}$-meson production on nuclei and nucleons observed in the Fermilab E665 experiment gives a solid evidence for the onset of color transparency. We propose the scaling relation between the $ρ^{0}$ and the $J/Ψ$ production, which further tests the mechanism of color transparency in exclusive (virtual) photoproduction.
We discuss the updated NMC determination of $F_2^n/F_2^p$ and $F_2^p - F_2^n$. Shadowing effects in deuterium make the structure functions determined by the NMC sensibly different from the true ones in the low--$x$ region. We show that the departure of $F_2^n/F_2^p$ and $F_2^p-F_2^n$ from the Regge expectations at small $x$ observed by the NMC likely disappears if one takes into account the shadowing corrections.
We show that there is no real conflict between the two determinations of the strange sea density from the opposite--sign dimuon production and from the difference of the $F_2$ structure functions measured in neutrino and muon deep inelastic scattering. Once non universal sea parton densities are introduced, which take into account the effects of different mass thresholds and different longitudinal contributions, the discrepancy is shown to disappear and both sets of data are simultaneously well reproduced. No need for a large strange sea content of the nucleon emerges.
We discuss the effects of the $s$-channel unitarization on the $x$ and $Q^{2}$ dependence of structure functions. The unitarization is implemented at the level of photoabsorption cross sections by resorting to the light--cone wave functions of virtual photons and to the diagonalization property of the scattering matrix in a basis of Fock states of the photon with fixed transverse size. Triple pomeron effects are also explicitly taken into account. We find large unitarity corrections to the structure functions at $x < 10^{-2}$. The results are in very good agreement with the existing NMC and the preliminary HERA data.
Color transparency predicts that, in $(e,e'p)$ reactions at large $Q^2$, the final-state interaction becomes weaker than the reference value predicted from the free-nucleon cross section. This reference value is usually evaluated in the dilute-gas approximation to Glauber's multiple-scattering theory. We derive the leading-order correction taking into account two-body correlations. Large cancellations are found so that the overall correlation effect is small.
We demonstrate how the virtual photoproduction of vector mesons on nuclei scans the wave function of vector mesons from the large non-perturbative transverse size $ρ\sim R_{V}$ down to the small perturbative size $ρ\sim 1/\sqrt{Q^{2}}$. Thee mechanism of scanning is based on color transparency and QCD predicted spatial wave function of quark-antiquark fluctuations of virtual photons. A rich, energy- and $Q^{2}$-dependent, pattern of the nuclear shadowing and antishadowing is predicted, which can be tested at the European Electron Facility and SLAC.
I present a new determination of the total cross section for proton-proton collisions from the recent Akeno results on absorption of the cosmic ray protons in the p-Air collisions. Extrapolation to the SSC energy suggests $σ_{tot}(p-p) \approx (160-170) mb$. I also comment on a possible sensitivity of the p-Air cross section determinations to assumptions on the inelasticity of nuclear collisions at high energy.
Colour transparency is a cute and indispensable property of QCD as the gauge theory of strong interaction. CT tests of QCD consist of production of the perturbative small-sized hadronic state and measuring the strngth of its non-perturbative diffraction nteraction in a nuclear matter. The energy depenednce of the final- state interaction in a nuclear matter probes a dynamical evolution from the perturbative small-sized state to the full-sized nonperturbative hadron. QCD observables of CT experiments correspond to a novel mechanism of scanning of hadronic wave functions from the large nonperturbative to the small perturbative size. In these lectures, which are addressed to experimentalists and theorists, I discuss the principle ideas of CT physics and the physics potential of the hadron and electron facilities in the > 10 GeV energy range. The special effort was made to present the material in the pedagigical and self-consistent way, with an emphasis on the underlying rich quantum-mechanical interference phenomena.
Quantum filtering of the ejectile wave packet from hard $ep$ scattering on bound nucleons puts stringent constraints on the onset of color transparency in $(e,e'p)$ reactions in nuclei at moderate energies. Based on multiple-scattering theory, we derive a novel formula for nuclear transparency and discuss its energy dependence in terms of a color transparency sum rule.