A. Szczurek

How to measure the pion structure function at HERA

Abstract We suggest a method of determination of the pion structure function down to x ⋍ 10 −4 based on semi-exclusive deep inelastic scattering off protons. The idea is to exploit the nonperturbative πN and πΔ Fock components of the nucleon, which contribute significantly to deep inelastic scattering and dominate the fragmentation of protons into fast neutrons and deltas. The intrinsic factorization properties of the semi-exclusive cross section give a good test for the validity of this approach.

Role of meson degrees of freedom in deep-inelastic lepton-nucleon scattering☆

Abstract Some aspects of the meson cloud around the nucleon for deep-inelastic lepton scattering are studied in the framework of the Sullivan formalism. We present a simple two-phase model of the nucleon. Renormalization of the valence-quark distribution due to the mesonic cloud is taken into account explicitly. We study the dependence of different quantities on the cut-off parameter of the form factor, the role of different mesons in deep-inelastic scattering, and SU(2)F symmetry breaking in the nucleon sea in connection to the Gottfried sum rule. It is possible to obtain agreement with the CCFR data using hard-meson NN form factors, which are almost consistent with the Bonn meson-exchange model. For full consistency the model requires a readjustment of quark distributions in the bare baryon to account for the dressing with the mesonic cloud. The E615 data on 1 2 (ū + d) − s restrict the cut-off parameter in the dipole form factor to about 1.2 GeV. For this value of the cut-off parameter we get the largest violation of the Gottfried sum rule, about half of that observed by NMC.

Meson cloud in the nucleon and d−u asymmetry from the Drell-Yan processes

Abstract Mesonic models predict violation of the SU(2) symmetry in the nucleon sea which seems to be necessary to explain the violation of the Gottfried sum rule. At the present time there is no generally accepted explanation of the effect. We find that careful analysis of the Drell-Yan processes in pp and pn collisions will provide complementary data to the Gottfried sum rule on the d − u asymmetry. We also find that some combinations of experimental results are insensitive to details of the mesonic models, offering the possibility to demonstrate the existence of the mesonic cloud in the nucleon.

Correlation effects in the final-state interaction for quasielastic (e, e' p) scattering

Abstract 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 Glaubers 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.Color transparency predicts that, in

Multiple-scattering effects in the transverse-momentum distributions from (e,e′p) reactions

(e,ep)

The onset of color transparency in (e,ép) reactions on nuclei

reactions at large

The Fermi-motion effect in the signal for color transparency in (e, e'p) scattering

Q^2

Pions in the light-cone nucleon and electromagnetic form factors

, 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 Glaubers 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.

Transition from meson to quark dynamics in the nucleon form factors

Abstract Within multiple-scattering theory we calculate the transverse-momentum distribution of struck protons in (e,e′p) reactions at CEBAF energies. At large p ⊥ we find significant contributions from multiple elastic rescatterings in the nucleus. These occur in regions where the effect of short-range nucleon-nucleon correlations is thought to play an important role, making the extraction of the latter more difficult. We also estimate the contribution of rescatterings to multi-nucleon emission processes.

Two-Body Components in the Nucleon Wave Function and their Consequences in Various Phenomena

Abstract 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,ep) 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 a realistic model. With increasing energy a slow onset is found.