Projectile fragmentation in hadron-nucleus collisions at high energies

Particle production in hadron-nucleus collisions at high energies is discussed in the projectile fragmentation region. The predictions of the constituent quark model are analyzed. The contribution of diffractive interactions is explicitly taken into account. Comparison with the recent Fermilab measurements shows good agreement with the quark model and strong effects of diffractive collisions in some of the analyzed reactions.     

Production of multibaryon clusters in hadron-nucleus collisions at high energies

The results obtained by analyzing the production of multibaryon clusters in π ⁻C and p ²⁰Ne interactions at momenta of 40 and 300 GeV/c, respectively, are presented.     

Semi-hard parton rescatterings in nuclear collisions at very high energies

Representing the semi-hard partonic interactions by the exchange of Lipatov's perturbative Pomeron, we express the semi-hard nuclear cross section as a self shadowing cross section. With the help of a generating functional technique, we obtain average numbers of multiple semi-hard partonic collisions without any need of using explicit expressions for the multi-parton distributions. The average number of semi-hard interactions of a given projectile parton against a target nucleus is estimated quantitatively and it is shown to grow very rapidly above one with increasing the c.m. energy.     

A model for multiplicity distributions in hadron-nucleon and α-α interactions at very high energies

We construct a simple stochastic model for particle production in hadron-nucleon collisions, which agrees with experimentally observed KNO scaling. We then use this model to calculate the multiplicity distribution of negative particles produced in α-α collisions at the CERN-ISR, based on a model of multiple collisions. The agreement of the measured spectra with the theory supports this hypothesis.     

Target fragmentation in hadron-nucleus collisions at high energy

We discuss target fragmentations in hadron-nucleus collisions at high energy (5–400 GeV). A model is developed which is based on the two-step (fast and slow) processes. A high-energy hadron drills a linear hole inside the nucleus, kicking out several nucleons (fast process). Along the linear hole, the target breaks up into a few pieces. One of the fragments forms an observed nucleus, absorbing some of the recoil nucleons (slow process). During the breakup, the Coulomb interaction between the fragment and the rest is taken into account. This leads to the consideration of a three-body breakup process which influences significantly the low-energy part of the energy distribution in the h+A → B+X reaction. The model is applied to the angular and the energy distributions in this collision. It achieves a nice agreement with experiment.     

Absolute differential, elastic integrated and moment transfer cross sections for electron--OCS collisions at intermediate and high energies

A complex optical model potential modified by incorporating the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds between atoms in a molecule, is firstly employed to calculate the absolute differential, elastic integrated and moment transfer cross sections for electron scattering by OCS over the incident energy range from 200 to 1000\,eV using the additivity rule model at Hartree--Fock level. The calculated results are compared with those obtained by experiment and other theories wherever available, and good agreement is obtained over a wide energy range. It is shown that the additivity rule model together with the modified potential is completely suitable for calculating the absolute differential, elastic integrated and moment transfer cross sections of electron scattering by molecules such as OCS.     

Topological cross-section in hadron-nucleus collisions and multiple scattering theory

The multiple scattering theory supplemented with AGK cutting rules is applied to calculation of the hadron-nucleus interaction cross-sections. In contrast to standard Glauber approach neither smallness of the interaction radius compared to the nuclear radii nor Gaussian form of thehN-interaction profile function are assumed. We consistently use the theory of the supercritical Pomeron. However all the results are more general and do not depend on the specific parametrization of the Pomeron pole ampletude. The region of validity of the widely used approximate formulae for topological and totalhA-interaction cross sections are discussed. It is discussed the novel features of particle-nucleus interactions at superhigh energies.     

Nucleus-nucleus collisions at high energies

Nucleus-nucleus collisions are studied in the framework of an extended Glauber model in which terms higher than the first (optical limit) in the phase shift expansion are considered. These are the so-called eclipse correction terms. The inelastic cross sections and distributions with respect to both the number of interacting nucleons and protons are calculated for various nucleus-nucleus interactions. The results show satisfactory agreement with the available experimental data.     

Dynamics of pp collisions at small impact parameters,universality of cross sections of hadron-hadron collisions and critical phenomena at superhigh energies

Studies of the small x dynamics at HERA energies allow one to quantify the range of momentum transfers and energies for which strength of the interaction approaches the maximum strength allowed by the unitarity in the gluon channel (black disk limit-BDL). Implications for the proton-proton interactions at collider energies (Tevatron, LHC) include a dominance of BDL up to transverse momenta of hadrons (jets) in the final state of a few GeV for collisions at small impact parameters, and explanation of proximity of the profile function of pp interaction to one at small impact parameters, leading to the universality of cross sections at superhigh energies. We discuss briey theoretical challenges in the applications of pQCD to small x phenomena, the onset of BDL for hard processes at large energies and universal limiting behavior: F ₂, xG ∝ ln³(x _o/x), σ(γ T) ∝ ln³(s/s _o). We explain that the onset of BDL should be accompanied by generic nonlinear phenomena for the produced states such as kinks, different symmetry of final states, etc and related tunneling transitions. Characteristic features of QCD physics of central collisions at ultrahigh energies correspond to a new regime: (i) interaction is dominated by hard interactions of quarks and gluons leading to disappearance of the soft physics and hadronic degrees of freedom, (ii) change with energy of the space-time evolution of produced quark-gluon states, (iii) change of the avor composition of the produced system, (iv) formation of a color network, etc. Hence, such collisions are likely to result in the production of new forms of the QCD matter. We also comment on the implications of the discussed physics for cosmic ray interactions at ultrahigh energies and on the methods to get information necessary for modeling cosmic rays at energies much higher than LHC using planned experiments at LHC.     

Three-jet cross sections in hadron-hadron collisions at next-to-leading order

We present a new QCD-event generator for hadron colliders which can calculate one-, two-, and three-jet cross sections at next-to-leading order accuracy. We study the transverse energy spectrum of three-jet hadronic events using the k(radially) algorithm. We show that the next-to-leading order correction significantly reduces the renormalization and factorization scale dependence of the three-jet cross section.     

A new space-time model for hadron-nucleus collisons at high energies

A new space-time model for hadron-nucleus collisions is proposed, where particles at the instant of creation are not only immature but their maturity rate is enhanced in the presence of other hadronic matter, as in a nucleus. With only one free parameter, the model can explain dn_A^p/dν, dn_A^π/dν, R_A^p(E_L), and the A-dependences of σ_in^pA and σ_in^πA.     

Topological cross sections in proton-proton interactions at 50 GeV

Project Thermalization (Experiment SERP-E-190 at IHEP) is aimed to study the pp interactions at 50 GeV with large number of secondary particles. In this report the experimentally measured topological cross sections have been presented taking into account the detector response and procession effciency. These data are in good agreement with gluon dominance model. The comparison with other models is also made and shows no essential discrepancies.     

The validity of the factorization hypothesis for nucleus-nucleus cross sections at high energies

We have calculated nucleus-nucleus cross sections for a variety of projectile and target nuclei and a wide range of energy. Total, reaction and elastic cross sections, as well as the slopes of the elastic diffraction peak, exhibit an approximate factorization property when the nuclei differ by less than 50% in r.m.s. radii. A simple geometrical interpretation is provided for the failure of factorization which occurs when target and projectile differ greatly in size.     

Measurement of neutral and charged current cross sections in electron-proton collisions at high Q^2

The inclusive single and double differential cross sections for neutral and charged current processes are measured with the H1 detector at HERA, in the range of four-momentum transfer squared between 150 and 30 000 GeV, and Bjorken x between 0.002 and 0.65. The data were taken in 1998 and 1999 with a centre-of-mass energy of 320 GeV and correspond to an integrated luminosity of 16.4 pb. The data are compared with recent measurements of the inclusive neutral and charged current cross sections. For clear evidence is observed for an asymmetry between and neutral current scattering and the generalised structure function is extracted for the first time at HERA. A fit to the charged current data is used to extract a value for the W boson propagator mass. The data are found to be in good agreement with Standard Model predictions. Received: 21 December 2000 / Published online: 15 March 2001