Quark–gluon plasma

The quark -gluon plasma ( QGP abbreviation ) is a state of matter in which the confinement of quarks and gluons is terminated; at high temperatures and / or Baryondichten they show a quasi- free behavior.

The quark -gluon plasma in nature

It is believed that the universe after the Big Bang went through this state in the first split seconds. In today's universe the QGP exists at most the center of neutron stars, some theories predict there another phase, to which are characterized by color superconductivity ( engl. color superconductivity ).

Production on earth

The use of heavy ion accelerators allows the exploration of the quark- gluon plasma ( QGPs ) in the laboratory. Corresponding experiments with particle accelerators are at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, the European nuclear research center CERN in Geneva and at the Relativistic Heavy Ion Collider ( RHIC ) on Long Iceland, New York (see press release below) performed. Here is the investigation of the phase transition from the confinement to the QGP is of particular interest.

At RHIC gold nuclei are brought to 99.9 % the speed of light in the accelerator ring and then successive shot. Particle with the resulting products are analyzed. The atomic nuclei disintegrate into tens of thousands of particles of matter due to the huge energies and temperatures (several trillion Kelvin). It can be shown that in the first nano- fraction of a second after impact pressure fluctuations inside the colliding particles in a manner to be compensated, which suggest a state of matter close like a liquid: a quark -gluon plasma is formed ( to form the QGPs see below).

Another indication of the occurrence of a QGP state analogous to a liquid in thermal equilibrium is a lower number of jets, ie conical Teilchenausbrüche from the colliding nuclei. This is explained with the fact that the particles so strongly decelerated by the QGP and thus be less energy, less energy for a jet remains.

Formation

The high energy density when penetrating two colliding nuclei can partons (ie quarks and gluons ) move quasi- freely. In this phase, the partons interact through inelastic collisions with each other until an equilibrium condition occurs; this is called a quark-gluon plasma. Due to the internal pressure of the plasma expands and cools down. If the critical temperature below which hadronization of partons begins. The so-called chemical equilibrium is reached when no further change the composition of the particle types. Find no inelastic interactions between the particles generated more instead, this is called thermal equilibrium.

Recent measurements at RHIC and LHC will take place at high energies and low particle densities ( baryochemischen potentials ). Present results suggest here a so-called "crossover " transition towards ( this is in contrast to a sharp " phase transition " only gradually, as it were " smeared "). Another indication of the existence of the QGP would be the detection of a first-order or second-order (critical point ) at higher potentials baryochemischen phase transition. The search for such transitions is carried out currently at RHIC or at the LHC and in the future at GSI.

Detection possibilities

Indirect detection options

The state of the Deco Fine Apartments, so the existence of the QGP is too short-lived to be detected directly without further can. In addition, the predictions of direct processes like energy density or temperature are strongly model-dependent. For this reason, indirect signatures have to be normally used.

One is the enrichment, ie the increased occurrence of strange quarks in the QGP or of strangeness -containing particles (eg, the φ - meson ) after hadronization ( Berndt Mueller, Johann Rafelski 1982). Reason: The energy required to produce a pair corresponds approximately to the temperature at which the resolution of nucleons and hadrons into quarks and gluons - and thus the formation of a QGP - is expected. Pairs are then propagated in the QGP produced by fusion of gluons. In addition, some energy states are occupied by lighter quarks, so that after a certain point the generation of pairs is preferred.

Other signatures include the suppression of relatively high-energy particles, which is caused by the high energy loss when traversing the QGPs, or the breaking up or melting of heavy quarkonia such as the J / ψ meson or the Υ - meson ( Helmut set, Tetsuo Matsui 1986).

A QGP detection requires measurement of many different signatures and a theoretical model for the QGP, which may explain these signatures. Based on numerical simulations and experimental results it is believed that the transition to the quark -gluon plasma takes place at a temperature of about 4.1012 Kelvin and belongs to the universality class of the three dimensional Ising model. Three-dimensional because of the four dimensions of special relativity at high temperatures eliminates the time variable; Ising model ( n = 1) because, as in this model ( up to sign ) dominates only one degree of freedom, for example, the strangeness and anti - strangeness degree of freedom. The given universality class have also ordinary liquids.

Direct evidence

Since the commissioning of the LHC at CERN in Geneva, an accelerator, which is currently ( early 2012 ) operating at 7 TeV and, among others, the production of quark-gluon plasmas due to collisions of Pb nuclei allowed, direct evidence became possible. It is reported in an article in the physics journal. The authors write: " The stopping power of the quark-gluon matter is so great that it can stop high-energy partons almost completely. This can already be seen in event images during data acquisition. "

Another probe are bound states of heavy quarks as the Bottoniums and their anti-quarks: Here you can see with the LHC in the comparison of the 1s, 2s and 3s states of the concrete, the plasma polarization as a change of the potential.

Molding

Earlier findings (as of August 2005 Source RHIC ) suggest that the cohesion between quarks and gluons in the quark-gluon plasma is not completely eliminated, but that there are strong interactions and mergers. The quark -gluon plasma behaves, at least at energies just above the energy of formation is more like a liquid ( but not like a superfluid! ) Than as a gas. Only at even higher energies the elementary particles gain complete freedom.

Since 2008 is also a discussion of a hypothetical precursor state of the quark-gluon plasma in progress, the so-called Glasma state. This corresponds to an amorphous ( glassy ) condensate, similar to so-called in solid state physics in some metals or metal alloys below the liquid state " metallic glasses " (ie amorphous metals ) gets.