Analysis ofx F 3: QCD and higher twist

We have analysed all available data on the non-singlet neutrino structure functionxF ₃ taking into account systematic errors and EMC corrections. A good fit to all data withQ ²≧5 (GeV/c)²,W ²≧10 (GeV/c)² is obtained neglecting higher twist contributions, with Λ=0.18±0.07 GeV, corresponding toα _s (Q ²=25(GeV/c)²)=0.18±0.02. On lowering the cuts toQ ²≧3 (GeV/c)²,W ²≧3 (GeV/c)², we find evidence for a small negative higher-twist term. Incorporating such a term in a simple parametrisation yields an increased Λ value of 0.27±0.05 GeV, corresponding toα _s (Q ²=25(GeV/c)²)=0.20±0.01.     

Two-loop QCD corrections to the coefficient functions of the deep inelastic structure functionsF 2 andF L

We present the analytic two-loop perturbative QCD corrections in the leading twist approximation to the coefficient functions of the operator product expansion for the second to tenth moments of the nonsinglet and singlet deep inelastic structure functionsF ₂ andF _L .     

Comparison of moments from the valence structure function with QCD predictions

We present moments (both ordinary and Nachtmann) of the nucleon valence structure function measured in high Q²_νFE scattering, supplemented by data from deep inelastic eD scattering. These data seem to agree with QCD predictions for vector gluons. The QCD parameter Λ is found to be of the order 0.5 GeV.     

New approach to the comparison of QCD predictions with deep inelastic data

It is pointed out that the use of Bernstein moments in the comparison with data of QCD predictions for the structure functions combines the advantages of standard moments analysis and direct structure function analysis.     

Renormalization scheme invariant analysis of the DIS structure functionsF 2 andF L

A renormalization scheme invariant analysis of the deep inelastic scattering structure functionF ₂ andF _L is performed. Expressions for the moments are given in this approach. We find a significant improvement of the agreement withR=σ _L /σ _T -SLAC data with respect to the conventional perturvative \((\overline {MS} )\) analysis. Higher twist corrections are also required confirming previous evidence.     

Filtered topological structure of the QCD vacuum: Effects of dynamical quarks

We systematically compare filtering methods used to extract topological structures on SU(3)$\mathit{SU}(3)$ lattice configurations. We show that there is a strong correlation of the topological charge densities obtained by APE and Stout smearing. To get rid of artifacts of these methods, we analyse structures that are also seen by Laplace filtering and indeed identify artifacts for strong smearing. The topological charge density in this combined analysis is more fragmented in the presence of dynamical quarks. A power law exponent that characterises the distribution of filtered topological clusters turns out to be not far off the values of an instanton gas model.     

Probing the QCD phase structure with higher order baryon numbersusceptibilities within the NJL model

Conserved charge fluctuations can be used to probe the phase structure of strongly interacting nuclear matter in relativistic heavy-ion collisions. To obtain the characteristic signatures of the conserved charge fluctuations for the quantum chromodynamics(QCD) phase transition, we study the susceptibilities of dense quark matter up to eighth order in detail, using an effective QCD-based model. We studied two cases, one with the QCD critical end point(CEP) and one without owing to an additional vector interaction term. The higher order susceptibilities display rich structures near the CEP and show sign changes as well as large fluctuations. These can provide us information about the presence and location of the CEP. Furthermore, we find that the case without the CEP also shows a similar sign change pattern, but with a relatively smaller magnitude compared with the case with the CEP. Finally, we conclude that higher order susceptibilities of conserved charge can be used to probe the QCD phase structures in heavyion collisions.     

Nuclear effects and higher twists in F3 structure function

We analyze the CCFR collaboration iron target data on the xF₃ structure function making particular emphasis on the extraction of the higher twist contributions from the data. Corrections for nuclear effects are applied in order to extract data on the structure function of the isoscalar nucleon. Our analysis confirms the observation made earlier, that the higher twist terms depend strongly on the level to which QCD perturbation theory analysis is applied. We discuss the impact of nuclear effects on the higher twist term as well as on the QCD scale parameter extracted from the fit to data. Received: 4 August 2000 / Accepted: 17 September 2000     

A method for an analysis of kinematical target-mass effects on the structure functions

An Altarelli-Parisi type evolution equation which incorporates kinematical target-mass effects is given by separating out purely kinematical parts from ones given by the perturbative QCD. Based on this separation, a simple method for an analysis of kinematical target-mass effects on the structure function is given.     

Momentum distribution of charged particles in jets in dijet events and comparison to perturbative QCD predictions

Inclusive momentum distributions of charged particles are measured in dijet events. Events were produced at the AMY detector with a centre of mass energy of 60 GeV. Our results were compared, on the one hand to those obtained from other e⁺e^?, ep as well as CDF data, and on the other hand to the perturbative QCD calculations carried out in the framework of the modified leading log approximation (MLLA) and assuming local parton–hadron duality (LPHD). A fit of the shape of the distributions yields Q_eff = 263±13 MeV for the AMY data. In addition, a fit to the evolution of the peak position with dijet mass using all data from different experiments gives Q_eff = 226±18 MeV. Next, α_s was extracted using the shape of the distribution at the Z⁰ scale, with a value of 0.118 ± 0.013. This is consistent, within the statistical errors, with many accurate measurements. We conclude that it is the success of LPHD + MLLA that the extracted value of α_s is correct. Possible explanations for all these features will be presented in this paper.     

The calculation of the hadron spectrum in lattice QCD with dynamical quarks

Hadron masses are calculated on an 8³×16 lattice using four flavors of staggered fermions to generate the gauge configurations, but using Wilson fermions to calculate the hadron propagators. The identification of a value of the Wilson hopping parameter with the value of the bare quark mass used in the simulations is discussed.     

Test of the QCD vacuum with the sources in higher representations

Recent accurate measurements [1, 2] of the static potentials between sources in various SU(3) representations provide a crucial test of the QCD vacuum and of different theoretical approaches to the confinement. In particular, the Casimir scaling of static potentials found for all measured distances implies strong suppression of higher cumulants and a high accuracy of the Gaussian stochastic vacuum. Most popular models are in conflict with these measurements.     

Q2-dependence of g 1 in the resonance region and higher twist effect

Based on the duality that both the inelastic and resonance physics languages work for the explanation of nucleon polarized structure functions at moderate Q², the higher twist effect on nucleon g₁ is predicted.     

NLO predictions for the growth ofF 2 at smallx and comparison with experimental data

We present parametrizations for the proton structure functionF ₂ in the next to leading order in perturbative QCD. We consider that the dominant term toF ₂(x, Q ²) should grow asx ^?ψ _s for smallx values, with the exponentλ _S being essentially independent ofQ ². Comparisons with the most recent H1 and ZEUS data confirm the valueλ _S ～0.35 obtained previously from fits to low energy data.