Polarized leptoproduction and dynamically generated spin-dependent parton distributions

The first moment of the polarized parton distributions of the proton is evaluated dynamically using the assumption that at some low resolution scale the proton consists of valence quarks only. The spin carried by gluons, ΔG, at the EMC resolution scaleQ ₀ ² =10 GeV² ispredicted to be ΔG/s _p ?5 withs _p=1/2 denoting the spin of the proton. This result furthermoreexplains the dynamical origin of the recent EMC measurement of the first moment of the polarized structure functiong ₁ ^P (x, Q ²).     

The role of the axial anomaly in measuring spin-dependent parton distributions

It is shown that forward matrix elements of j₅^μ, the flavor singlet axial vector current, do not merely measure the helicity carried by quarks and antiquarks but also include a spin-dependent gluonic component due to the anomaly. In perturbation theory the exact value of the gluonic component depends on the infrared regulator, and we argue that computing off-shell matrix elements with zero-mass quarks gives the proper method of regulation to exhibit the chiral properties of the theory. We suggest measuring two-jet production in deep inelastic scattering off polarized targets as a means of determining the spin-dependent gluonic component of j₅^μ.     

Study of parton spin-dependent distributions in hard proton-proton collisions through measurement of handedness

Polarization of partons emitted in hard scattering of an unpolarized proton beam from a polarized hydrogen target can be found through a measurement of jet handedness. Two definitions of handedness are suggested with zero and essentially nonzero contributions of gluon jets. A sensitivity of the handedness to the valence, sea quark and gluon distributions is considered. Handedness properties under the charge conjugation and flavorSU (2) transformations are investigated. An option to study the spin-dependent parton distributions in hard scattering of the unpolarized HERA proton beam from the polarized internal hydrogen target is discussed.     

Two-spin asymmetry in\mathop p\limits^{( - )} p reactions and spin-dependent parton distributions

The two-spin asymmetries \(A_{LL}^{\pi ^0 } (\mathop p\limits^{( - )} p)\) and \(A_{LL}^\gamma (\mathop p\limits^{( - )} p)\) are calculated in a new model incorporating the nonrelativistic quark model and the parton model which interprets well EMCg ₁ ^p (x) data. The model can reproduce the experimental data for inclusive π⁰ rather well.     

QED corrections to the evolution of parton distributions

We study the systematic inclusion of QED corrections in the evolution of parton distributions. corrections modify the evolution equation for parton distributions. They introduce additional parton distributions, like the photon distribution in the nucleon, and lead to additional mixing effects. We discuss the modifications for a realistic model of N_f,up up-type flavours and N_f,down down-type flavours. We have implemented these corrections into a numerical program and we quantify the size of these effects in a toy model. The corrections reach the order of 1%.     

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.     

A semianalytical method to evolve parton distributions

We present a new method to solve in a semianalytical way the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution equations at NLO order in the x-space. The method allows to construct an evolution operator expressed in form of a rapidly convergent series of matrices, depending only on the splitting functions. This operator, acting on a generic initial distribution, provides a very accurate solution in a short computer time (only a few hundredth of second). As an example, we apply the method, useful to solve a wide class of systems of integrodifferential equations, to the polarized parton distributions.     

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.     

Charm production and parton distributions

Recent accurate data on F ₂(x,Q) and on F ₂ ^c (x,Q) from HERA at small-x require a more precise treatment of charm production in the global analysis of parton distributions. We improve on existing global QCD analyses by implementing the leptoproduction formalism of Aivazis et al. which represents a natural generalization of the conventional zero mass QCD parton framework to include heavy quark mass effects. We also perform analyses based on the fixed-flavor-number scheme, which is widely used in the literature, and demonstrate their uses and limitations. We discuss the implications of the improved treatment of heavy quark mass effect in practical applications of PQCD and compare our results with recent related works.     

Polarized parton distributions of the photon

The polarized parton distributions of the photon are determined by imposing a VMD valence-like structure at some low resolution scale. Experimental tests at high energyep colliders are studied for inclusive single photon orW-boson production.     

Generalized parton distributions of the photon

We present a first calculation of the generalized parton distributions of the photon (both polarized and unpolarized) using overlaps of light-front wave functions at leading order in α and zeroth order in αs; for non-zero transverse momentum transfer and zero skewness. We present the novel parton content of the photon in transverse position space.     

Generalized parton distributions in the deuteron

We introduce generalized quark and gluon distributions in the deuteron, which can be measured in exclusive processes like deeply virtual Compton scattering and meson electroproduction. We discuss the basic properties of these distributions and point out how they probe the interplay of nucleon and parton degrees of freedom in the deuteron wave function.     

Spin-dependent parton distributions and structure functions

Nuclear parton distributions and structure functions are determined in an effective chiral quark theory. We also discuss an extension of our model to fragmentation functions.     

Nonperturbative parton distributions and the proton spin problem

The Lorentz contracted form of the static wave functions is used to calculate the valence parton distributions for mesons and baryons, boosting the rest frame solutions of the path integral Hamiltonian. It is argued that nonperturbative parton densities are due to excitedmultigluon baryon states. A simplemodel is proposed for these states ensuring realistic behavior of valence and sea quarks and gluon parton densities at Q² = 10 (GeV/c)². Applying the same model to the proton spin problem one obtains Σ₃ = 0.18 for the same Q².     

Diffractive parton distributions from the saturation model

We review diffractive deep inelastic scattering (DIS) in the light of the collinear factorization theorem. This theorem allows one to define diffractive parton distributions in the leading twist approach. Due to its selective final states, diffractive DIS offers interesting insight into the form of the diffractive parton distributions which we explore with the help of the saturation model. We find Regge-like factorization with the correct energy dependence measured at HERA. A remarkable feature of diffractive DIS is the dominance of the twist-4 contribution for small diffractive masses. We quantify this effect and make a comparison with the data. Received: 22 February 2001 / Revised version: 22 March 2001 / Published online: 3 May 2001     

Spin distributions in the quark parton model

Spin-dependent parton distributions are described in a broken SU(6) quark parton model. The model predicts definite forms for the spin-dependent structure functions in deep inelastic lepton-nucleon scattering and leads to several relations between Regge intercepts and couplings. Resonance electroproduction at large momentum transfer is explored via Bloom-Gilman duality.