The stuff nuclear matter is made off
More than 99.9% of the mass of an atom is found in the nucleus. As a consequence,
nuclear matter, the stuff nuclei are made of is more than 1014 times denser
than normal matter, e.g., water. A piece the size of a lump of sugar would
weigh about 300 million tons.
How does nuclear matter react when it is compressed and heated? Can one
produce new forms or phases of matter? To answer these questions, physicists
want to collide heavy nuclei at more than 95% of the velocity of light.
In such nucleus-nucleus collisions, highly compressed and heated matter
is produced for a very tiny time-span of less than 10-22 seconds. The compression
phase is followed by an explosive expansion phase with many hundreds of
particles being emitted. The traces of all these particles which can be
measured by huge detectors, provide new insights into the dynamics of supernova
explosions and the behavior of neutron stars.
Of special interest is the possible transition to a new form of matter that might exist in the
interior of neutron stars. At very high densities and temperatures, the nucleons are expected to
dissolve into their constituents and to form a plasma, consisting of quarks, gluons, and other
particles - the so-called quark-gluon plasma. Physicists suspect that in the early universe,
about 1 millisecond after the Big Bang, such a phase transition occurred in the opposite direction
from the quark-gluon plasma into hadronic matter, i.e. into our present-day matter, which is governed
by protons and neutrons (and electrons).
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Computer simulation of the collision of two uranium nuclei at the maximum energy privided by the new facility.
- Quicktime
version (4.9MB)
- AVI
version (8.5MB)
The illustration shows the phase diagram of hadronic matter as predicted by theory.
It plots the temperature in units of one million electronvolt against the density in units of normal nuclear density ρ0.
At very high temperatures and densities, physicists expect that the quarks and their bonding particles, the
gluons - normally locked up inside the nucleons - become liberated from their confinement
and move as free particles in a so-called quark-gluon plasma.
The detectors designed for the FAIR-facility must be capable of identifying and measuring the path of up to
thousand different particles that emerge from a single nucleus-nucleus collision event - at a
repetition rate of one million per second. These specifications and the extremely high data rates involved
represent a challenge for new developments in detector instrumentation, electronics and information technology.
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