Volume 30, Issue 3, May 1999
30(1999); http://dx.doi.org/10.1134/1.953105View Description Hide Description
These lecture notes illustrate the application of Dyson–Schwinger equations in QCD. The extensive body of work at zero temperature and chemical potential is represented by a selection of contemporary studies that focus on solving the Bethe–Salpeter equation, deriving an exact mass formula in QCD that describes light and heavy pseudoscalar mesons simultaneously, and the calculation of the electromagnetic pionform factor and the vector-meson electroproduction cross sections. These applications emphasize the qualitative importance of the momentum-dependent dressing of elementary Schwinger functions in QCD, which provides a unifying connection between disparate phenomena. They provide a solid foundation for an extension of the approach to nonzero temperature and chemical potential. The essential, formal elements of this application are described, and four contemporary studies are employed to exemplify the method and its efficacy. They study the demarcation of the phase boundary for deconfinement and chiral symmetry restoration, the calculation of bulk thermodynamic properties of the quark–gluon plasma, and the response of π- and ρ-meson observables to T and μ. Along the way a continuum order parameter for deconfinement is introduced, an anticorrelation between the response of masses and decay constants to T and their response to μ is elucidated, and a mirroring of the slow approach of bulk thermodynamic quantities to their ultrarelativistic limit is highlighted. These effects too are tied to the momentum-dependent dressing of the elementary Schwinger functions.
30(1999); http://dx.doi.org/10.1134/1.953106View Description Hide Description
30(1999); http://dx.doi.org/10.1134/1.953107View Description Hide Description
This review presents an overview of the methods of detecting and determining the main parameters of superdense hadronic matter created in ultrarelativistic nuclear collisions. Questions related to the quark–hadron phase transition and the conditions under which it is realized are discussed, and various approaches to describing the evolution of nucleus–nucleus collisions are analyzed: microscopic Monte Carlo generators and hydrodynamical models. The basic tests proposed for the experimental study of the properties of nuclear matter under extreme conditions are studied. Possible interpretations are given of the features observed in experiments on relativistic nuclear collisions at existing accelerators (AGS, SPS), compared with the corresponding hadron–hadron collisions: broadening of the hadron momentum spectra, increased yield of low-mass dileptons, enhanced strange-particle production, suppression of the Ψ-resonance yield, and so on. The prospects for future experiments at the RHIC and LHC colliders are discussed. Special attention is paid to hard probes, which give information about the early stages of evolution of the hot, strongly interacting matter. Model representations are used to analyze the effects expected as a result of the passage of hard jets of color-charged partons through the dense matter, and the matter parameters primarily affecting the jet characteristics and their experimental identification are determined. The question of identifying hard QCD jets in heavy-ion collisions on the background of large statistical fluctuations of the transverse energy flow due to the large secondary-particle multiplicity is also discussed.
30(1999); http://dx.doi.org/10.1134/1.953108View Description Hide Description
A summary is given of the current status of lattice investigations of quantum chromodynamics at finite temperature. After a brief introduction into the formulation of QCD on the lattice and into the treatment of lattice QCD in numerical simulations, the current knowledge about the critical temperature of the transition from the hadron to the quark–gluon plasma phase is presented. The status of investigations of the nature of this transition is discussed. Moreover, analyses of the equation of state in the high-temperature phase as well as computations of the excitation spectrum at nonvanishing temperature are presented.
30(1999); http://dx.doi.org/10.1134/1.953109View Description Hide Description
The Nuclotron is the first superconductingsynchrotron intended for the acceleration of high- energy nuclei and heavy ions. The accelerator is designed to provide beams of relativistic particles with energies up to 6 GeV per nucleon. The accelerator was put into operation five years ago at the Joint Institute for Nuclear Research in Dubna near Moscow. The cryogenic system of the Nuclotron includes three helium refrigerators. Each of them has a nominal capacity of 1600 W at 4.5 K. These refrigerators cool the accelerator ring, which has a perimeter of 251.5 m and a “cold” mass of about 80 tons. The ring of the Nuclotron comprises 96 dipole magnets 1.5 m long and 64 quadrupolelenses 0.45 m long. The magnetic field of about 2 T is configured with a “cold” iron yoke and a hollow superconductor inside which the two-phase helium flows. There are 28 correctors 0.31 m long with three or four types of windings in each, twelve 6 kA helium-cooled current leads, 234 leads of 100 A current for correcting windings, and also about 600 sensors of cryogenic temperatures. The experience of using novel technical solutions in the design of the Nuclotron cryogenic system is described.