Physics of collisions between ultrarelativistic nuclei: Manifestation of collective effects

Experimental results concerning heavy-ion collisions studied by means of the Relativistic Heavy-Ion Collider (RHIC) at an energy of 100 GeV per nucleon and showing manifestations of collective effects are surveyed. These effects are interpreted as a consequence of the formation of a dense thermalized medium referred to as quark-gluon plasma (strongly interacting quark-gluon plasma, quark-gluon matter, parton medium). An azimuthal anisotropy of particles, the suppression of the particle yield at high transverse momenta in relation to proton-proton collisions, and a change in the shape of the peak from a hadron jet in nucleus-nucleus collisions are spectacular manifestations of collective effects.     

Dynamics of Ξ-hyperon production on nucleon

A phenomenological model of Ξ-hyperon production from nucleons by antikaons is developed. The model successfully reproduces available experimental data on integral and differential cross sections of the reaction in the different charge channels at the center-of-mass energies from the threshold up to 3.2 GeV. It is shown that the baryonic (u-channel) exchange is the dominant reaction mechanism.     

Modeling complex plastic deformation and fracture of metals under disproportionate loading

A mathematical model is developed to describe fatigue-damage accumulation in structural materials (metals and their alloys) on multiaxial paths of disproportionate combined heat and power loading. The effect of the shape of the strain path on the fatigue life of metals was studied to obtain qualitative and quantitative estimates of the obtained constitutive relations. It is shown that the proposed constitutive relations adequately describe the main elastoplastic deformation effects and damage accumulation in structural materials for arbitrary strain paths.     

Observation of exotic meson production in the reaction pi- p --> eta'pi- p at 18 GeV/c

An amplitude analysis of an exclusive sample of 5765 events from the reaction pi- p-->eta'pi- p at 18 GeV/c is described. The eta'pi- production is dominated by natural parity exchange and by three partial waves: those with J(PC) = 1(-+), 2(++), and 4(++). A mass-dependent analysis of the partial-wave amplitudes indicates the production of the a2(1320) meson as well as the a4(2040) meson, observed for the first time decaying to eta'pi-. The dominant, exotic (non- qq) 1(-+) partial wave is shown to be resonant with a mass of 1.597+/-0.010(+0.045)(-0.010) GeV/c2 and a width of 0.340+/-0.040+/-0.050 GeV/c2. This exotic state, the pi1(1600), is produced with a t dependence which is different from that of the a2(1320) meson, indicating differences between the production mechanisms for the two states.     

Two-dimensional discrete wavelet analysis of multiparticle event topology in heavy ion collisions

The event-by-event analysis of multiparticle production in high energy hadron and nuclei collisions can be performed using the discrete wavelet transformation. The ring-like and jet-like structures in two-dimensional angular histograms are well extracted by wavelet analysis. For the first time the method is applied to the jet-like events. The jet positions are located quite well by the discrete wavelet transformation of angular particle distribution even in the presence of soft process background in nucleus-nucleus collisions at LHC energies.     

The influence of temperature on the swelling of polyacrylic and polymethacrylic cationites

Temperature was shown to substantially influence the swelling of KB-2e3 polyacrylic and KB-4P2 polymethacrylic ionites cross-linked by triethylene glycol dimethacrylate (TEGDM) and divinylbenzene (DVB). Maximum swelling changes as the temperature increased were observed for the Ca form of the KB-4P2 ionite. Swelling and contraction of polymethacrylic cationite grains as the temperature decreased and increased occurred at equal fairly high rates, whereas the sorption of water by the polyacrylic cationite in the calcium form cross-linked by TEGDM occurred much more slowly than desorption.     

Phenomenological model for the \overline{{K}}N \rightarrow K \Xi reaction

A phenomenological model for the $ \overline{{K}}$ N $ \rightarrow$ K $ \Xi$ reaction is suggested. The model includes s and u channel exchanges by $ \Lambda$ , $ \Sigma$ , $ \Sigma$ (1385) , and $ \Lambda$ (1520) and s channel exchanges by above-threshold hyperonic resonances. The explicit expression for the propagator for a particle with spin 7/2 is presented. High-mass and high-spin resonances play a significant role in the process. We deal with the whole set of existing experimental data on the cross-sections and polarizations in the energy range from the threshold to 2.8GeV in the center-of-mass system and reach a good agreement with experiments. Applications of the model to other elementary reactions of $ \Xi$ production and to $ \Xi$ hypernuclear spectroscopy are briefly discussed.     

Elliptic flow of particles in heavy-ion collisions and possibility of its observation at the LHC energies

The azimuthal anisotropy of particle distributions is one of the important observables that characterize collective effects at the initial stage of the formation and expansion of quark-gluon matter in collisions of relativistic nuclei. It is expected that an increase in energy from RHIC to LHC values will be accompanied by the growth of the azimuthal-anisotropy coefficient υ ₂ and the growth of nonflow effects (contribution of minijets and other correlations between particles). In the present study, methods for determining the azimuthal-anisotropy coefficient υ ₂ are analyzed on the basis of events simulated with the aid of the HYDJET generator for Pb + Pb collisions at the LHC energies, the contribution of nonflow effects being estimated. The accuracy of measuring the coefficient υ ₂ as a function the transverse momentum and pseudorapidity under experimental conditions at LHC is assessed.