Scaling and non-scaling in a rest frame quark-parton model of the proton

Electron-proton deep inelastic scattering is treated as the incoherent scattering of electrons by bound Dirac partons in the proton rest frame. An approximate bound state wave function is used for the initial parton, while the final parton is considered free. A good fit is obtained to the structure function F₁(x,Q²) in the range x > 0.15, Q² > 2 GeV. The subsequent prediction for F₂(x,Q²) is not as good, indicating a small additional contribution by longitudinal photons for W < 2.5 GeV. The parton momentum distribution is found to contain transverse momentum of 400–600 MeV, increasing with x.     

QCD cascade model in deep inelastic scattering

We develop a new QCD cascade model for jets in deep inelastic scattering. We use the light-like axial gauge whose gauge vector is parallel to momentum of the initial parton so that only final partons cascade. Due to this feature we can generate events for any given virtualityQ ² andx _B =Q ²/2Pq.     

Nuclear effects in deep inelastic scattering of charged-current neutrino off nuclear target

The nuclear effects in the neutrino–nucleus charged-current inelastic scattering process is studied by analyzing the CCFR and NuTeV data. The structure functions F₂(x,Q²) and xF₃(x,Q²) as well as differential cross sections are calculated by using CTEQ parton distribution functions and the EKRS and HKN nuclear parton distribution functions, and these are compared with the CCFR and NuTeV data. It is found that the corrections of the nuclear effect to the differential cross section for the charged-current antineutrino scattering on the nucleus are negligible, the EMC effect exists in the neutrino structure function F₂(x,Q²) in the large x region, the shadowing and anti-shadowing effect occur in the distribution functions of valence quarks in the small and medium x region, respectively. It is also found that shadowing effects on F₂(x,Q²) in the small x region in the neutrino–nucleus and the charged-lepton–nucleus deep inelastic scattering processes are different. It is clear that the neutrino–nucleus deep inelastic scattering data should further be employed in restricting the nuclear parton distributions. PACS 13.15.+g; 24.85.+p; 25.30.-c     

Jets and quark confinement in the covariant parton model

A parton model incorporating quark confinement is discussed which (a) reproduces conventional parton model cross sections for deep inelastic lepton scattering and for large-p_T hadronic phenomena, (b) leads to final state jets and (c) accounts for the similar multiplicities observed in hadronic and lepton induced final states at low p_T.     

Partons and their applications at high energies

We discuss Feynman's parton model for deep inelastic weak or electromagnetic processes as an application of the impulse approximation to elementary particle interactions. The special features and conditions permitting this application are elaborated upon in some detail including the dependence of the parton model and the impulse treatment on an appropriate choice of coordinate frames and the role of the very soft or “wee” partons. Application of the parton model is made to the calculation of the cross section for massive lepton pair production in very high energy hadron-hadron collisions and compared with experiment. The conjectured role of light cone singularities in describing this and the other deep inelastic amplitudes is also discussed.     

Simple tests of quark-nucleon reciprocity

The inclusive cross-section for the production of a single hadron in deep inelastic electroproduction is studied in a dual resonance model. The Bjorken scaling behaviour in the virtual photon fragmentation region for finite x (≡ 2p_L^c.m./√s) is (1/σ^{T,L))d3σT,L/E?}d³p ～ (1/q²) F(x,p_⊥²/q²) and thus the transverse momentum grows like q², whereas in the parton model (1/σ^T,L)d³σ^T,L/E^?1d³p ～ F(x,p_⊥²). A related effect is the absence of two-jet structure in e⁺e^? annihilation. We believe that dual model results may give a more reliable indication of the deep inelastic behaviour for composite hadrons than the parton model.     

Perturbative quantum chromodynamics

A large variety of modern perturbative aspects of QCD is critically reviewed from a theoretical as well as phenomenological point of view. The first part of this review is devoted to the classical more formal approach of summing leading logs: After a brief discussion of the basic concepts of renormalization theory, we review the renormalization group and its predictions for the effective (running) coupling constant in any field theory (asymptotic freedom as well as ‘fixed point’ theories). Using, in addition, the operator product expansion for deep inelastic scattering we calculate scaling violations of structure functions and show how to compare these results with experiment. Furthermore, dynamical calculations of parton distributions are discussed, as well as σ_L/σ_T, jets in leptoproduction and subleading corrections. We then proceed to show how these renormalization group improved results can be also derived using a simple perturbative language (Kogut-Susskind; Altarelli-Parisi) or by summing parton (Bethe-Salpeter) ladders. The universal validity (process independence) of the resulting Q² dependencies of parton distributions is emphasized and their factorization from the uncalculable non-perturbative piece (infrared divergences) is discussed. These latter results enable us to make rather unambiguous predictions for processes other than deep inelastic scattering, to which the remainder of this review is devoted. The hard scattering processes discussed indetail include hadronic (Drell-Yan) production of lepton pairs as well as their transverse momenta, the hadronic production of heavy quark flavors, semi-inclusive processes and fragmentation functions, high-p_T reactions and some recent topics and problems of jet production in e⁺e^? annihilation.     

Semi-inclusive deep inelastic lepton scattering in a pion cloud model

In this note we explore the consequences of the pion cloud model for semi-inclusive deep inelastic lepton scattering. We argue that by scattering on a few-nucleon target, the detection of the recoiling target would provide a valuable test of the meson cloud model. We estimate the semi-inclusive cross section for deep inelastic lepton scattering on a³He target, as function of Bjorkenx and target recoil momentum.     

Structure functions and parton distributions

We review recent developments in the determination of parton densities from deep inelastic and related data. We show how the asymmetries observed in theW ^± rapidity distributions and inpp/pn Drell-Yan production further constrain the partons at moderatex.     

Partons and the EMC spin effect

We focus on the parton model and the role of the axial anomaly in polarised deep inelastic scattering. We show that the axial anomaly is relevant to each of the higher moments of the spin dependent structure functiong ₁ (x) and not just the first moment. This result implies that the factorisation of mass singularities is not sufficient to define the parton model in spin dependent QCD. (It is certainly a necessary condition.) We also need to consider the locality of the photon parton interaction. The anomaly is observed over allx in the EMCg ₁ (x) data.     

Functions of the nucleon structure and determination of the strong coupling constant

The properties of deep inelastic scattering at high energies, as well as results of fitting of experimental data on structure functions, obtained by BCDMS, SLAC, NMC, and BFP collaborations in fixed target experiments, with the aim of determining the strong coupling constant, the shape of parton distributions, and power corrections to F ₂(x, Q ²), are presented.     

A possibility of asymptotic freedom without non-Abelian gauge theories

We discuss solutions of the renormalization group equations for a Yukawa field theory. For an increasing effective boson mass we find that the leading terms in the vertex functions in the high-energy region are given by diagrams which contain no internal boson lines. In e⁺e^? annihilation into hadrons we get the parton model formula R(s) = Σ_iQ_i², whereas in the deep inelastic e^?p scattering the simple parton model behaviour is modified by the (in general) non-canonical dimension of the quark field.     

On the hadron-parton reciprocity relation

The possibility of an equality between the distributions of partons inside hadrons and the distributions of hadrons in parton fragmentation is studied. It is consistent with existing electroproduction data when the momentum fractions involved are not too small. Implications for current-hadron interactions, large p_T hadronic cross sections and heavy lepton pair production in hadron-hadron collisons are discussed.     

Structure functions and parton distributions

We review recent developments in the determination of parton densities from deep inelastic and related data. We show how the asymmetries observed in theW ^± rapidity distributions and inpp/pn Drell-Yan production further constrain the partons at moderatex.     

Form factors,threshold relations,and large angle elastic scattering of pions

The form factor F(q²) of the pion in a simple core model is investigated, together with the deep inelastic electroproduction structure function, F₂(ω). A relation between these two, analagous to the Drell-Yan-West relation for nucleons, is derived and it is found that F₂ is related to either the form factor or the square of the form factor depending on how rapidly F(q²) ultimately falls with momentum transfer. The unitarity equation and its implications for this kind of threshold relation are discussed. The simple core model is also applied to elastic large angle ππ scattering.     

New results on deep inelastic processes from generalized vector dominance

A formulation of generalized vector dominance (GVD), consistent with the parton model (PM) for deep inelastic electroproduction, is presented. The parton distributions at small x are correctly predicted in terms of the photoabsorption parameters. It is found that no charmed partons exist in the sea of the nucleon. The pomeron ??_c coupling and the ?_c ? photoproduction cross section are negligible. The ratio σ_L/σ_T for deep inelatic and diffractive electroproduction is found to be small. This is related to the prediction that the highest Regge singularity coupled to longitudinal vector mesons is a cut with intercept minus one. In the time-like region it implies that the angular distribution in e⁺e^?→ π + X is ～ (3?cos²Θ), in consistence with experiment and disagreement with PM. Finally the large value of σ(e⁺e^? → hadrons) is attributed to a series of ?_c's.     

SU(6) symmetry breaking effects in deep inelastic scattering

The fact that the N and Δ states of the $\text{56}$ baryons are not degenerate in mass is shown to imply that the deep inelastic scattering ratio F_2n(x)/F_2p(x) should approach $\text{1}\text{4}$ as x → 1. The rate of approach is predicted to be approximatel linear in x. The possibility of observing analogous effects in other large momentum transfer processes is also discussed.