Forward-backward multiplicity correlation in high energy hadron-hadron collisions

The forward-backward multiplicity correlation over the full pseudorapidity range forpp andp \(\bar p\) collisions at ISR and Collider energies have been analysed in terms of a Chou-Yang Type multiplicity distribution which consists of a stochastic (binomial) component forz=n _F ?n _B and a nonstochastic (negative binomial) component forn=n _F +n _B . Reasonable agreement with experimental data is obtained if the final-state particles are assumed, in a cluster model, to be created by the decay of clusters with a mean cluster size (charged particles per cluster) which is energy-dependent.     

Jet energy density in hadron-hadron collisions at high energies

The average particle multiplicity density dN _ch/dη is the dynamical quantity that reflects some regularities of particle production in the low-p _T range. The quantity is an important ingredient of z scaling. Experimental results on charged particle density are available for pp, pA, and AA collisions, while experimental properties of the jet density are still an open question. The goal of this work is to find the variable that will reflect the main features of the jet production in a low transverse energy range and play the role of the scale factor for the scaling function ψ(z) and variable z in data z-presentation. The appropriate candidate is the variable we called “scaled jet energy density.” The scaled jet energy density is the probability of having a jet with defined E _T in defined x _T and pseudorapidity regions. The PYTHIA6.2 Monte Carlo generator is used for calculation of the scaled jet energy density in proton-proton collisions over a high energy range and at η = 0. The properties of the new variable are discussed and sensitivity to “physical scenarios” applied in the standard Monte Carlo generator is noted. The results of the calculations of scaled jet energy density at LHC energies are presented and compared with predictions based on z scaling. The text was submitted by the authors in English.     

Spin effects in high energy hadron-hadron scattering

The spin-flip amplitudes of the meson-nucleon and nucleon-nucleon scattering are calculated in the framework of the dynamic model taking into account the interactions at large distances. The consideration of the strong form factors at the corresponding vertex and prea-symptotic contributions allowed us to describe correctly the differential cross sections and spin effects of hadron-hadron scattering at high energies. On this basis predictions at high and superhigh energies are made.     

Forward hadron-hadron scattering at high energy

The high energy elastic scattering of pp, , pπ⁺, pπ⁻, pk⁺ andpk ⁻ processes is studied at forward directions. The expressions for total scattering cross-sections and the ratios of real-to-imaginary parts of the forward amplitude are derived inP+f model. For the Regge part of the scattering amplitude, the standard form is taken. For the pomeron part, the Harari-Freund conjecture is assumed. The background is assumed to get dominant contributions from the multiparticle exchanges in that channel. These contributions are obtained by parametrising the branch cuts by conformal mapping and polynomial expansion methods. The agreement with the experiment is good. The fits suggest strong exchange degeneracy forpp andkp which in turn is consistent with the Harari-Freund duality.     

Charmed particle production in hadron-hadron collisions

In the framework of Quark-Gluon-String Model developed recently in ITEP we calculate spectra of charmed particlesD,D _s,Λ_c,Ξ_c,Ω_c in hadron-hadron collisions taking into account the decays ofS-wave resonances like D^*,D_s ^*,Σ_c,Σ_c ^*,Ξ_c ^*,Ξ_c ^′, and Ω_c ^*. We describe the bulk of the existing data onD, D^*, adΛ _c production in πp andpp collisions and predict the yield of charmed particlesin Σ^?p and Ξ^?p reactions at hyperon beam energies of 340 GeV/c and 600 GeV/c. Because of significant production of baryon resonances our predictions for unfavored fragmentation differ from predictions of other models which do not take resonance production into account.     

Heavy quark pair formation in hadron-hadron collisions

The scalar and pseudoscalar variants of strong interaction theory are used to find the full section for heavy quark pair formation in quark-antiquark and gluon-gluon collisions. With this assumption the section for formation of j/ mesons in nucleon scattering on nucleons is calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 30–34, September, 1981.The author is indebted to M. P. Rekalo for his constant interest in the study.     

Charged particle multiplicity distribution in hadron-hadron collisions

The multiplicity distributions of charged particles emitted frompp and \(\bar p\) p collisions at 15 centre of mass energies from \(\sqrt s = 9.8\) to 900 GeV are interpreted in a two-component model. The leading component arises from the fragmentation of the excited leading particles. The non-leading or central component consists of hadrons resulting from the decay of clusters emitted from a fireball. The energy dependence of the parameters of this model is computed and their behaviour is compared with the predictions of the single negative binomial distribution. Predictions at supercollider and at infinite energies are discussed.     

Particle composition and clustering in hadron-hadron collisions

Particle composition in hadron-hadron collisions is discussed in connection with clustering production of hadrons. The effective Lagrangians for the decay processes of theC -andC -type clusters are introduced. The particle composition is calculated by using the flavorSU(3) symmetry. The calculated results for particle composition as well as averaged transverse momenta are in agreement with ISR, SPS and Tevatron data.     

Observation of exclusive electron-positron production in hadron-hadron collisions

We present the first observation of exclusive e(+)e(-) production in hadron-hadron collisions, using pp[over] collision data at (square root) s = 1.96 TeV taken by the run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532 pb(-1). We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy E(T) > 5 GeV and pseudorapidity |eta| < 2. With these criteria, 16 events are observed compared to a background expectation of 1.9+/-0.3 events. These events are consistent in cross section and properties with the QED process pp[over] --> p + e(+)e(-) + p[over] through two-photon exchange. The measured cross section is 1.6(-0.3)(+0.5)(stat) +/- 0.3(syst) pb. This agrees with the theoretical prediction of 1.71+/-0.01 pb.     

On the role of longitudinal momenta in high energy hadron-hadron scattering

We demonstrate a new method to calculate inelastic scattering cross-sections, which in contrary to the Regge-based methods takes into account the energy momentum conservation law. It is shown that the main contribution to integral expressing inelastic scattering cross-sections does not come from the multi-Regge domain. In particular, accounting for the longitudinal momenta contribution to virtualities is sufficient and results in the new mechanism of cross-section growth. The reasons for taking into account the sufficiently high number of interference contributions are shown and the approximate method for this purpose is developed. By fitting single free parameter of the model achieved a qualitative agreement of the total and inelastic cross sections with experimental data.     

On clustering effects and phase instabilities in high energy nuclear collisions

On the basis of a nuclear matter model calculation at finite temperature it is shown that at densities of about 1/15 of normal nuclear mattor density a new metastable phase exists which is determined by cluster formation effects. The existence of a low density isomer might be related to the recently observed anomalous short reaction mean free paths from 2 GeV/N heavy ion collisions.