QUARK MATTER FORMATION AND ULTRA-RELATIVISTIC ION COLLISIONS

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Submitted on 1 Jan 1982

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QUARK MATTER FORMATION AND ULTRA-RELATIVISTIC ION COLLISIONS

L. van Hove

To cite this version:

L. van Hove. QUARK MATTER FORMATION AND ULTRA-RELATIVISTIC ION COLLISIONS.

Journal de Physique Colloques, 1982, 43 (C3), pp.C3-174-C3-174. �10.1051/jphyscol:1982339�. �jpa-

00221892�

JOURNAL DE PHYSIQUE

Colloque C3, suppZ4ment au n o 12, Tome 43, Gcembre 1982 page C3-174

QUARK

MATTER

FORMATION

AND

ULTRA-RELATIVISTIC ION COLLISIONS

L. Van Hove

TH Division, CERN, CH-1211,Geneva 23, Switzerland

Strong theoretical evidence, mainly based on lattice calculations, points to the existence of a new state of bulk hadronic matter, the quark-gluon plasma, at temp- eratures 2 200 MeV and/or net quark densities 2 3 f r 3 . The nature of the deconfine- ment transition from hadron gas to quark-gluon plasma is not known, but indications

-

are that it is sharp, has large latent heat and a large change of entropy density.

There is weaker theoretical evidence for the restoration of chiral symmetry in hadronic matter. The indications are that this chiral transition occurs at higher temperature and/or net quark density than the deconfinement transition.

Crude theoretical estimates based on extrapolations of the available data suggest that the accumulation

of

co-moving energy and the compression of nuclear matter in- near head-on ultra-relativistic collisions of heavy ions may be sufficient to reach the plasma phase of hadronic matter. To improve these estimates one needs systematic ion-ion data for a wide range of nucleon numbers A, A', at E

>

10-20 GeV (where E is the c.m. energy per nucleon-nucleon collision). Before such data become available, quantitative predictions as to the energies and nucleon numbers required for plasma formation are impossible to make. What is clear is that high energies are called for, despite the rather low deconfinement temperature.

For plasma formation in the central region, any increase of incident energy should increase the accumulation of co-moving energy. In contrast, a saturation effect is expected for the nuclear fireballs in the fragmentation regions. There is hope that plasma formation may be more likely in exceptional collisions characterized by high multiplicity and/or high transverse energy. This possibility deserves to be ex- plored theoretically and experimentally.

The most likely signals for plasma formatinn are believed to be direct dileptons and photons (which could be produced in the plasma throughout its lifetime), and strange particles (which could probe the strange to non-strange (anti) quark ratio in the plasma just before hadronization~).

T h e o r e t i c a l s should be continued on the space-time evolution of hadronic matter in ion-ion collisions at ultra-relativistic energies, including simple models for thermalization, entropy production, longitudinal and lateral expansion, hadroniza- tion. Experimental- on ultra-relativistic ion-ion collisions are needed to study the conditions f'or possible plasma formation, the dependence of the proposed signals on energy and baryon number of the incident ions, and the nature of the exceptional collisions mentioned above. Much work could be done with accelerators already ex- isting.(e.g., heavy target experiments at the CERN Super-Proton-Synchrotron accelerating light ions) or under construction (Brookhaven ISABELLE as heavy ion colliding beam machine )

.

For detailed reviews of the status of the field and of experimental possibilities we refer to the Proceedings of the Workshop on Quark Matter Formation and Heavy Ion Collisions (Bielefeld, 10-14 May 1982), M. Jacob and H. Satz, editors, World Scientific Singapore, to appear.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982339