Extreme States of Matter by Vladimir E. Fortov

Author:Vladimir E. Fortov
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Also investigated was the expansion mode of the cigar-shaped bunch upon imparting it an additional energy or terminating the traps current (Fig. 6.49). One can clearly see the ellipticity of the cloud expansion, which is similar to the elliptic fluxes of quark-gluon plasma. In this case the momentum has a dimension , where δ is the interparticle distance. The shear viscosity is of the form . The dimensionless quantity α has the meaning of the ratio between the de Broglie wavelength and the interparticle distance. For the air α ≈ 6000, for water α ≈ 300, which testifies to the smallness of quantum effects in this case [233]. However, for liquid helium α ≈ 1 at the point, which corresponds to the quantum mode. Viscosity calculations performed for strongly interacting Fermi systems give α ≈ 0. 3 [44].

The theoretical description of oscillatory processes of plasmas in traps was the concern of paper [45], where a hydrodynamic approximation was substantiated and the characteristics of spectral density for excitations were found.

As we saw in Sect. 6.3, the production of quark-gluon plasma (QGP) in the relativistic collision of heavy nuclear is attended with the emergence of a low-viscosity (ideal) fluid, whose dynamics is described by the hydrodynamics of an ideal liquid consisting of quarks and gluons.

Since detectors record the late expansion stages of quark-gluon plasma, it is possible to judge its characteristics by indirect indications (see Sect. 6.3); the most substantive of them are the data about the “streams” of expanding substance and “hard” processes corresponding to the high values of angular momentum. The hard processes include the production of quarks and the generation of highly collimated hadron jets due to quark collisions in the QGP. On the face of it, this contradicts the principle of asymptotic freedom [110], which predicts a weakening of interactions in the QGP with increase in temperature and density.

Nevertheless, experiments clearly show the formation of “elliptica” streams (Figs. 6.41 and 6.44) in off-center collisions, which are confidently reproduced by hydrodynamic collision simulations. This also is a verification for the description of relativistic collisions by the methods of continuum mechanics under local thermodynamic equilibrium.

In the motion through a dense QGP, the jets experience absorption (suppression), which signifies that the quark-gluon plasma is strongly opaque to them. This effect of jet suppression is illustrated by Fig. 6.58 borrowed from [110], where electrons are indicative of the decay of heavy quarks. Interestingly, since photons are not subject to strong interactions, they are hardly (see Fig. 6.58) absorbed by the QGP. They can therefore carry information about the QGP temperature, which turned out [110] to lie in the 300–600 MeV range and well above the temperature of the phase transition to the QGP, T c ≈ 170 MeV.

Fig. 6.58Suppression of jets and heavy-quark hadrons in a quark-gluon plasma (QGP) (a); plot of the suppression of pions and yield of electrons with a high transverse momentum p t in head-on collisions of gold nuclei. The suppression coefficient the ratio between the particle yield and those products which may be expected from a simple superposition of proton-proton collisions allowed in the QGP. Pions

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.