On high energy leptoproduction

The particle distributions and the event structures in high energy leptoproduction are considered in a model where perturbative QCD is used to compute the cross sections to order α _s and the Lund jet model is used for the soft hadronization process. Since complete events are generated by a Monte Carlo program not only single-particle spectra can be studied but also various correlations, thus making a more detailed comparison between theory and experiment possible. The model is found to be in agreement with data from the European Muon Collaboration. We indicate how a one-particle trigger can be used to study an enriched sample of two forward jet events, and exhibit a useful experimental test for the existence of such events with the properties predicted by perturbative QCD. We also indicate how to gain further information on the confinement and soft fragmentation mechanisms.     

Fractality in rapidity space and low temperature intermittency in multihadron processes

We study intermittency effects in high energy collisions introducing a fractal measure in rapidity space and formulationg the hadronization sector of the S-matrix within the Ginzburg-Landau approach. The properties of the critical Feynman-Wilson fluid provide us with a boundary condition forT=T _c whereas a low temperatures (T?T _c ) a strong amplification of the intermittency effect is found, corresponding to a local minimum of the effective free energy. The significance of this solution for the interpretation of the intermittency phenomenon for low multiplicities is discussed and a comparison with experimental measurements is attempted, within the two-component model.     

Energy flow and energy correlations in deep inelastic scattering

We study two examples of infrared-safe quantities in deep inelastic scattering: the flow of energy in a given angular range and the energy-energy angular pattern. We derive expressions for these quantities in perturbative QCD, to order α_s, and show explicitly their infrared safety. Our formulas for the angular energy flow and the energy-energy angular pattern depend only on well-defined QCD factors and on the deep inelastic structure functions. To gauge whether or not these perturbative QCD results are applicable to present day data, we estimate in a simple model the effects of hadronization and primordial parton transverse momentum. In general these non-perturbative effects mask the resulting QCD pattern at present energies, but vanish more rapidly at higher energies than the QCD effects. However, we point out two examples where it may be possible to test the perturbative QCD predictions with available data. One of them involves studying the x-dependence of the azimuthal asymmetry of the energy flow. The other involves studying the angular width of the energy-energy correlation function.     

Novel mechanisms of baryon number flow over large rapidity gap

It is shown that slow valence quark in the wave function of high energy proton can fragment into a baryon if the fast diquark-spectator is destroyed, i.e. is turned from the antitriplet to the sextet colour state. We estimated the cross section of the baryon number flow to the central rapidity region using the perturbative QCD. It depends on the rapidity gap Δy as exp (-Δy/2) and nicely agrees with the data at ISR energies, There exists also an intriguing possibility to transfer baryon number by means of gluonic exchanges only. This contribution does not depend on rapidity at all and becomes sizable in TeV energy region. We propose also new mechanisms for baryonantibaryon production from vacuum, transfer of polarization over large rapidity intervals, and nuclear stopping power.     

The transverse hadronic energy inW andZ 0 production

A thorough analysis is presented of the hadronic transverse energy produced in association withW ^± andZ ⁰ weak bosons atp \(\bar p\) colliders. The complete rapidity and transverse energy distributions are derived, including the perturbative annihilation and Compton terms and the resummation of soft gluons. The first non leading corrections to the corresponding Sudakov exponent are included in full and their effects are discussed. To make contact with the actual data a number of non perturbative inputs is also necessary. We extract this information from minimum bias measurements. A detailed comparison of the resulting theoretical predictions with the available experimental data is finally presented.     

A model for central charm production inpp collision

The major part of central charm production inpp collision is proposed to arise from a charm \((D\bar D)\) component in the hadronization of the scattered quark. We use the charm hadronization model previously developed to explain the like sign dimuon events in neutrino scattering. Thus we have a parameter free prediction for the central charm crosssection relative to thepp total cross-section. The predicted cross-section agrees with data in magnitude as well as in its energy, Feynmanx andp _T dependence.     

Squark and gluino production at the pp collider

We present detailed calculations of the missing energy and jet signatures for squark and gluino pair-production at the CERN $\text{p}\text{p}$ collider, incorporating three improvements over previous analyses. These include smearing in transverse momentum at production, the fragmentation of supersymmetric partons into supersymmetric hadrons, and the hadronization of their decay products as well as of the residual jets. We find that previous estimates of supersymmetric signatures are not substantially altered by the inclusion of smearing and fragmentation. We present rapidity and transverse momentum distributions for both primary and secondary jets, and discuss variations in the trigger conditions which could increase the number of two-jet events and help discriminate between different models for the monojet events. We find that gluinos give fatter jets than do squarks of the same mass, although it is not easy to understand the thinness of the observed monojets if they are due to squarks of mass O(40) GeV. We emphasize that the key feature to clarify the supersymmetric interpretation of missing p_T events is the study of secondary jet production in mono- and dijet events.     

Two-particle azimuthal and rapidity correlations in intervals of transverse momentum in π+ p-interactions at 250 GeV/c

A multi-dimensional analysis of two-particle correlations in π⁺ p-interactions at 250 GeV/c shows interesting structure. Particularly strong positive shortrange rapidity and azimuthal correlations are observed for low-p _T like sign pairs. This observation is not reproduced by models used for comparison (FRITIOF, DPM, quark gluon (multi)string model). A possible explanation is Bose-Einstein interference not included in these models.     

The Reggeon Field Theory and finite scales at collider energies

The Reggeon Field Theory (RFT) with attention paid to finite “flavoring” rapidity scales is considered in the light of emerging SPS collider data. Predictions from a simple RFT perturbative model made in 1978 are shown to be consistent with σ_tot and other data, in both theP?f identity andP+f versions. The RFT scaling laws are judged not applicable without large non-leading terms, implying an asymptotic region beyond the collider.     

Vector boson production at colliders: A theoretical reappraisal

We study the production of vector bosons in hadron-hadron collisions via the Drell-Yan mechanism in QCD. Our treatment of the transverse momentum and rapidity distributions of the produced bosons takes all available theoretical principles and results into account in a systematic way. The resulting q_T distribution reduces to the perturbative limit for large q_T, includes the summation of soft gluons and reproduces the known results for the total cross section. A full numerical analysis of W and Z cross sections at collider and tevatron energies is made.     

Low energy QCD predictions from non perturbative methods

We show that by using lattice results about the euclidean ?-propagator, it is possible to give theoretical predictions on the low energy behavior of thee ⁺ e ^?→had. cross section. Furthermore, we present a comparison of perturbative QCD results (plus certain sum rules corrections) with non perturbative results from the lattice in the intermediate energy region.     

Characteristics of heavy flavour production inep collisions

The production of heavy flavours inep collisions at the HERA energy is studied using a model based on boson-gluon fusion into a heavy quark-antiquark pair followed by gluon emission and string hadronization. Total cross-sections and dependence on basic kinematical variables are given as well as distributions of the most important variables at both the quark and hadron level, e.g. rapidity and transverse momentum. Charm, bottom and top production is compared and signatures for their separation are discussed in terms of decay muons and global event shape properties.     

Study of highp ⊥ quark and gluon jet fragmentation

The fragmentation properties of highp _⊥ jets are investigated using new data from the ISR and the SPS collider. Effects from gluon radiation are clearly demonstrated by comparison with a state-of-the-art model inlcuding QCD parton cascade evolution and string hadronization, which gives in general good agreement with the data. Differences between quark and gluon jets are discussed as well asQ ₂-dependent scaling violation effects.     

Cumulant expansion for the p–d model: density of states and hole occupation

We propose a nonstandard perturbative solution of the p - d model, based on a generalized cumulant expansion. Using a temperature dependent Green's functions formalism, the behaviour of the density of states and the hole occupation number is investigated in the charge-transfer and in the Mott-Hubbard regime, to describe realistic systems with CuO₂ sheets. A comparison with different analytic and numerical methods is also discussed.     

On the anomalous large transverse energy events observed in proton-lead scattering

It has been shown that a study of correlation between the average rapidity, 〈y〉, and transverse energy,E _T , can be used to distinguish between different origins of large transverse energy events observed inp-Pb scattering in the HELIOS experiment. If the largeE _T events are to be attributed to a nuclear dependence of structure functions then the hard scattering picture implies a positive correlation among the above two quantities, contrary to that seen in experiment.     

Charm photo-and electroproduction at high energies

The differential and total cross sections for the photoproduction of vector D* mesons and for their production in deep-inelastic interactions at the HERA collider are estimated on the basis of a model motivated by perturbative calculations within QCD. The proposed model makes it possible to take into account higher twists in the meson transverse momentum at pT～m _c and to reproduce correctly the dominance of c-quark fragmentation for p _T m _c . The possibility of the hadronization of an octet c $\bar q$ state into a meson is considered, whereby good agreement with experimental data is obtained both for the case of D*-meson photoproduction and for the case of D*-meson formation in a deep-inelastic process.