........ published in NEWSLETTER # 64
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........ published in NEWSLETTER # 64
CORRELATIONS AND CLUSTERING PHENOMENA IN SUBATOMIC PHYSICS
by Professors M.N. Harakeh, J.H. Koch and O. Scholten, Rijksuniversiteit/K.V.I., Groningen (The Netherlands)
In many areas of physics the major outstanding problem is to obtain a firm grasp of correlation phenomena. In many cases, average properties are fairly well understood, but the correlations in the system, which are crucial for its properties, are only poorly understood. It is the aim of the present volume (NATO ASI SERIES B359) to set out the similarities and differences in the treatment and effects of correlation phenomena in the various fields of physics with emphasis on the field of nuclear physics.
In order to calculate accurately the binding energies of A<8 nuclei at the keV level, it is important to take into account two- and even three-body correlations in the wave function. Pandharipande has shown how the required accuracy can be achieved by first optimising a variational wave function which contains Jastrow correlations as well as three-body correlations and by cooling this trial wave function in a second stage by a Greens-function Monte-Carlo technique. For heavier nuclei and even nuclear reactions, a different variational approach is developed by Horiuchi which is built on the ideas of the cluster models.
Maltfliet emphasised the importance of correlation phenomena in the description of non-equilibrium processes which are responsible for phenomena such as Anderson localization. A quantum transport equation is derived that includes two-nucleon correlation effects.
As explained by Grabmayr, the correlations in the nucleus can be determined fairly precisely in nucleon knockout reactions with real or virtual photons. In his lectures, Trautman showed that another manifestation of these nucleon correlations is through fragmentation in nuclear reactions.
An interesting speculation for many years has been the possible existence of di-baryon resonances. In his contribution, Clement discusses its first possible observation in double-charge-exchange reactions.
Correlation physics on a quark scale was presented by Koch, Carlson and Schukraft. In perturbative QCD the quark correlations related to hard processes, i.e. short-length scales, are investigated. At longer-length scales much of the physics related to the pion is governed by chiral symmetry and its spontaneous breaking in the basic QCD Lagrangian. A phase transition is predicted to occur at high nuclear temperatures, which are within experimental reach at the large accelerators, corresponding to the restoration of the chiral symmetry. The thus-created Disoriented Chiral Condensate gives rise to definite observables. The size of the hot fire-ball formed in nuclear reactions can be measured by exploiting Hanburry-Brown Twiss correlations (Heinz).
In the contribution by Icke, physics on extremely large (the universe) and extremely small (the Planck scale) scales are described.
Reference books: B35, B318, B359