J.L. Meunier

QCD corrections to the Drell-Yan mechanism and the pion structure function

Abstract We compute the differential cross section d σ /d Q 2 d y for lepton pair production up to first order in the strong coupling constant α s . We show that, in the region where the theory applies and where the statistical accuracy of the experiments is good, the ratio of the QCD correction to the Drell-Yan cross section is approximately constant, and that its magnitude is in good agreement with the results of the CERN-NA3 experiment. We thus show that, within the framework of this first-order calculation, the shape of the pion structure function extracted from dilepton production in πp collisions is approximately correct. We also comment on the average transverse momentum of the dilepton due to gluon or quark recoil.

The Role of Soft Gluons in Lepton Pair Production

Abstract We derive expressions for the exponentiation of soft gluon effects in lepton pair production and discuss their phenomenological implications for the rapidity and Q 2 dependence of the so-called “K- factor ” . Predictions are given for scaling violations to be seen in the determination of the pion structure function.

Angular intermittency in QCD jets

Using two methods, via fluctuations and correlations, an analytical formula is derived for the factorial multiplicity moments in a QCD jet at the Double Leading Logarithm accuracy. The resulting self-similar dependence on the solid-angle cell size is characteristic of an intermittency behaviour in angular variables. The intermittency indices depend on the diffusion angle through the running of αS. Physical features of jet fluctuations such as collimation at large angles and saturation at small angles are well described in the perturbative framework. A parameter-free prediction of angular intermittency is proposed for Z0 decays into hadrons, assuming hadronparton duality.

Azimuthal correlations in P- or Q-factorized cluster production

Abstract The study of the mean value 〈 p ·1 · p ·2 〉 ( y 1 , y 2 ) in P- or Q-factorized cluster proceduction indicates the presence of mean range azimuthal correlations in multiperipheral (Q-factorized) cluster production, and gives test for the size of the mean transverse momentum of the clusters.

A study of QCD scaling violations by direct resolution of Altarelli-Parisi type equations

Abstract We present a detailed study of scaling violations for non-singlet, singlet and glue distribution functions in the framework of several approximation schemes of QCD. Our formalism consists of direct resolution of the Altarelli-Parisi type equations and leads to a simple exponential form for the function q ( x , Q 2 ). This form is very suitable for the analysis of experimental data and for the exploration of different evolution schemes. In particular, we examine the implications on the QCD scaling parameter Λ and the gluon parameter n G .

Mass singularities at finite temperature in a scalar field theory

Using as a model the φ3 field theory in space-time dimensionD=6, we show the validity of the Kinoshita-Lee-Nauenberg theorem at finite temperature to first order in the coupling constant.

Elastic scattering and transverse momentum correlations in multiperipheral models

Abstract We compute the overlap function and transverse momentum correlations in various versions of the multiperipheral model. We examine in particular how close to saturation is the bound for the pomeron slope recently derived by Krzywicki. Correlations between neighbouring transverse momentum transfers in the S-matrix element are shown to be able to bring the multiperipheral model in agreement with experiment. We also study the case of cluster production and suggest a possible improvement of Krzywickis bound.

Compound poisson distributions and KNO scaling

Abstract We propose to represent the multiplicity distribution by a compound Poisson distribution suggested by unitary or absorptive multiperipheral models. In this framework, we discuss the scaling law proposed recently by Koba, Nielsen and Olesen, and in particular the behaviour of non-asymptotic terms. We show that our model is in very good agreement with the present experimental data.

Intermittency, fragmentation, and the Smoluchowski equation

Abstract Using a recently found transformation property of the Smoluchowski equationfor aggregation kinetics, one finds a one-to-one equivalence between aggregation kinetics with additive coefficients and a specific class of semi-random cascading models describing intermittent fragmentation in e.g. multi-particle physics. As shown in detail for the brownian case and extended to homogeneous scaling solutions, the same non-linear equation which describes aggregation as time flows to infinity, admits a fragmentation solution in a different range of time. The obtained cascading depends on a new evolution variable non-trivially related to time. The parameters describing the overall multiplicity distribution and the intermittency patterns of local fluctuations are both related to the Smoluchowski kernels.

Leading particles, energy momentum conservation and the approach to scaling in inclusive reactions

Abstract It is shown that the leading particle effect is responsible, via energy-momentum conservation, for a s −1 2 rise of the inclusive spectra at y = 0, corresponding in Mueller language to a secondary Regge singularity with intercept zero.