B. G. Zakharov

Colour transparency and scaling properties of nuclear shadowing in deep inelastic scattering

AbstractWe present the perturbative QCD analysis of nuclear shadowing in the deep inelastic scattering at smallx in terms of the spatial wave function ofqn

Scaling properties of nuclear shadowing in deep inelastic scattering

bar q

The BFKL-Regge phenomenology of deep inelastic scattering

n fluctuations of virtual photons. The wave function formalism makes it quite obvious that shadowing is the scaling, rather than the higher twist, 1/Q2, effect, contrary to a numerous recent claims. We demonstrate explicitly how the scaling shadowing comes from the large, hadronic, size quarkantiquark pairs even in the limit ofQ2→∞, and why it should very slowly, ∞1/log (Q2/m2) decrease at very largeQ2. We argue in favor of the scaling triple-pomeron contribution to the nuclear shadowing and present predictions for a cross section of diffraction dissociation of virtual photons and for the mass spectrum of diffraction excitation, which can be checked at HERA and Fermilab. We predict strikingly different scaling properties of diffraction dissociation and nuclear shadowing for the longitudinal and transverse photons. Our, numerial predictions for shadowing are in good agreement with the recent EMC data.

Nucleon sea parton densities. Differences for neutrinos and muons

We study scaling properties of the diffraction dissociation of virtual photons in a deep inelastic scattering. We concentrate on the total diffraction dissociation rate, diffraction excitation mass spectrum and the pomeron structure function to the lowest order in perturbative QCD. We calculate the valence structure function and the strangeness and charm content of the pomeron and estimate the ocean structure function using the pomeron factorization property. We find that quarks carry ≈ 10% of pomerons momentum. Differential cross section of the (virtual) photon-pomeron scattering is found to exhibit features typical of the hadronic two-body reactions, supporting a treatment of the Pomeron as a particle, whereas the flavor dependence of structure functions does not support the particle treatment of the pomeron. Diffraction dissociation of photons is predicted to make ≈ 15% of the total deep inelastic scattering rate at smallx and largeQ2. Detailed predictions for the mass spectrum and angular distribution of jets produced on the valence component of the pomeron are presented.

Preasymptotics of colour transparency

Abstract We present the perturbative QCD analysis of nuclear shadowing in deep inelastic scattering and prove it to be the scaling, rather than the higher twist, 1/ Q 2 , effect, contrary to numerous recent claims. We argue in favor of the scaling triple-pomeron contribution to the nuclear shadowing and comment on the mass spectrum of diffraction excitation by highly virtual photons. Our numerical predictions for shadowing are in good agreement with the recent EMC data.

On the determination of the Weinberg angle from neutrino reactions

We describe the nuclear structure functions in the whole range of the Bjorken variablex, by combining various effects in a many-step procedure. First, we present a QCD motivated model of nucleons, treated, in the limit of vanishingQ2, as bound states of three relativistic constituent quarks. Gluons and sea quarks are generated radiatively from the input valence quarks. All parton distributions are described in terms of the confinement (or nucleons) radius. The results for free nucleons are in agreement with the experimental determinations. The structure functions of bound nucleons are calculated by assuming that the main effect of nucleon binding is stretching of nucleons. The larger size of bound nucleons lowers the valence momentum and enhances the radiatively generated glue and sea densities. In the small-x region the competitive mechanism of nuclear shadowing takes place. It also depends on the size of the nucleons. By combining stretching, shadowing and Fermi motion effects (the latter confined to very largex), the structure function ratio is well reproduced. Results are also presented for theA-dependence of the momentum integral of charged partons, the nuclear gluon distribution and the hadron-nuclei cross sections.

Longitudinal structure functions

We calculate the Regge trajectories of the subleading BFKL singularities and eigenfunctions for the running BFKL pomeron in the color dipole representation. We obtain a viable BFKL-Regge expansion of the proton structure function F2p(x,Q2) in terms of several rightmost BFKL singularities. We find large subleading contributions to F2p(x,Q2) in the HERA kinematical region which explain the lack of predictive power of GLDAP extrapolations of F2p(x,Q2) to the region of small x. We point out the relation of our early finding of precocious BFKL asymptotic behavior to the nodal structure of subleading BFKL eigenfunctions.

BUILDING THE GLUON DISTRIBUTION IN NUCLEONS

Abstract The nucleon sea parton distributions probed by muons and neutrinos are different since excitation of s s , c c pairs by muons and c s , s c pairs by neutrinos have different mass thresholds. Natural starting points for the structure functions are cv(x, Q2) ≈ sv(x, Q2), in v ( v ) interactions and cμ(x,Q2) ⪡ s μ(x, Q2) in μ interactions. Up to ∼ 20% corrections to the conventional predictions for the neutrino structure functions at small x are predicted. The effects we discuss are in leading twist and persist numerically up to large values of Q2.