An analysis of quantum chromodynamic structure function beyond leading order

We obtain approximate solutions of Altarelli-Parisi equations beyond leading logarithmic approximation. Our results suggest quantitative utility of higher order terms in the structure function analysis of deep inelastic scattering.     

Direct photon production beyond leading order in QCD

The significance of the quark-quark scattering process (quark+quark→quark+quark+photon) for the production of large-q_T real photons is discussed in the framework of perturbative QCD. To extract the finite contribution of this process to the differential cross section dσ/dy d²q_T (hadron 1+hadron 2→photon+anything) we define the gluon distribution and the quark-to-photon fragmentation function beyond the leading approximation. The calculations are performed consistently in the dimensional regularization scheme. Our numerical estimates show the resulting finite qq→qqγ contribution to be a small (order α_s/2π) correction in comparison with the basic QCD subprocesses.     

Largep T double photon production in hadronic collisions-beyond leading logarithm QCD calculation

We calculateO(α _s ) corrections to largep _T double photon production in hadronic collisions. We find that these corrections to the basic \(q\bar q \to \gamma \gamma \) subprocess are important, preventing to describe double photon production on the basis of the leading logarithm approximation only. We give a phenomenological discussion of the results obtained at SPS, ISR and \(Sp\bar pS\) energies. In particular, we investigate how the effect of the intrinsic parton <K _T> may be disentangled from the perturbative contribution. We also calculate the aplanarity distribution characteristic of 3 jet events.     

The deep Compton scattering: Single photon spectrum and photon-hadron correlations beyond leading logarithms

We have calculated higher order QCD corrections to the Deep Inelastic Compton single inclusive cross-section. The perturbation expansion seems to be well behaved: the corrections are small and the fully corrected cross-section depends little on the factorization scale which is chosen. A complete phenomenological study at SPS, Tevatron and HERA energies is performed and theoretical predictions tend to be in good agreement with preliminary experimental data. The corrections to the double inclusive cross-section (σ(γp→γhX) are also calculated and found to be small in the region of physical interest for σ(γp→γπ⁺ X)?σ(γp→γπ^? X)     

Flux confinement in the leading logarithm model

We study the statics of quasi-abelian quark and antiquark source charges in the approximation in which leading logarithm radiative corrections are retained in the gauge gluon effective action functional. We show that the partial differential equation for the flux function is of degenerating elliptic type, leading to flux confinement within a free boundary which is a characteristic. The static potential increases linearly for large source separations, with a logarithmic subdominant term.     

Moments of the virtual photon structure function

The photon structure function is a useful testing ground for QCD. It is perturbatively computable apart from a contribution from what is usually called the hadronic component of the photon. There have been many proposals concerning this nonperturbative part of the real photon structure function. By studying moments of the virtual photon structure function, we explore the extent to which proposed nonperturbative contributions can be identified experimentally.     

Second-order QCD analysis of the photon structure function

The QCD predictions for the photon structure function are reexamined with particular emphasis on the small-x behavior. A simple parametrization of the real photon structure function, free of 1/x singularity, is derived. The structure function is found to be sensitive at small x to the non-perturbatively calculable constant term in the n = 2 moment, and we show that the problem of a negative structure function can be solved on the basis of the knowledge of this single non-perturbative parameter.     

Gluon distributions in real and virtual photon and the photon structure function

Gluon distributions in real and virtual photons are calculated using evolution equations in the NLO approximation. The quark distributions in the photon determined on the basis of the QCD sum rule approach in [1] are taken as an input. It is shown that gluon distribution in the photon can be reliably determined up tox=0.03÷0.05, much lower than the corresponding values in the case of quark distributions. Two variants of the calculations are considered: (1) it is assumed that there are no intrinsic gluons in the photon at some low normalization pointQ ²=Q ₀ ² ∼1GeV²; (2) it is assumed that gluonic content of the photon at lowQ ₀ ² is described by gluonic content of vector mesonsρ, ω, ϕ. The gluon distributions in these two variants appear to be different. This fact permits one to clarify the origin of nonperturbative gluonic content of the photon by comparing the results with experiment. Structure functionsF ₂(x) for real and virtual photon are calculated and it is shown that in the regionx≥0.2 where QCD approach is valid, there is a good agreement with experiment.     

Strong coupling constant from the photon structure function

We extract the value of the strong coupling constant alpha(s) from a single-parameter pointlike fit to the photon structure function F(gamma)(2) at large x and Q(2) and from a first five-parameter full (pointlike and hadronic) fit to the complete F(gamma)(2)data set taken at PETRA, TRISTAN, and LEP. In next-to-leading order and the MS renormalization and factorization schemes, we obtain alpha(s)(m(Z))=0.1183+/-0.0050(expt)(+0.0029)(-0.0028)(theor) (pointlike) and alpha(s)(m(Z))=0.1198+/-0.0028(expt)(+0.0034)(-0.0046)(theor) (pointlike and hadronic). We demonstrate that the data taken at LEP have reduced the experimental error by about a factor of 2, so that a competitive determination of alpha(s) from F(gamma)(2) is now possible.     

The QCD leading behaviour of the polarized photon structure functions and possible experimental test

In this paper we calculate the leading contributions to the polarized photon structure functions using general Altarelli-Parisi equations. We also discuss the possible experimental test for asymmetry in the two-photon production of hadrons via the process e⁺+e⁻→e⁺+e⁻+x.