The Relativistic Heavy Ion Collider at the Brookhaven National Laboratory (BNL) took first collision data in June-September, 2000. The collider has two intersecting rings with counterpropagating beams. Below you see some initial images from head-on collisions of gold nuclei with a total energy of 26 TeV (65 GeV/nucleon in each beam). In such a collision most of the nucleons dissolve into a fireball of hot vacuum. A total of up to 5000 particles is ejected from this tiny but extremely hot region of the vacuum as it expands and cools. Temperatures achieved are comparable to that of the universe about 10 microseconds after the Big Bang. The experimental program studies matter at such extremes of temperature and pressure that nucleons melt into a quark-gluon plasma (QGP) in which the quantum number `color' used to describe the fundamental structure of the nuclear force is liberated from its ordinary confinement within nuclear particles.
The images below were made by Tom Trainor and Duncan Prindle of the University of Washington using data obtained by the STAR detector (Solenoidal Tracker at RHIC). Particles passing through a gas mixture inside a TPC (Time Projection Chamber) leave tenuous trails of ionization. These trails or particle tracks drift in an electric field to the ends of the chamber and are amplified and digitized in 100 nanosecond slices. The resulting data (20 MB/collision - 1 collision/second) are processed on a farm of PCs to reconstruct the particle tracks, which can then be visualized as you see below. The colors represent the momenta of the particles in analogy with the solar spectrum: red - low momentum through violet - high momentum. The active volume of the STAR dector is a cylinder 4 meters long and 4 meters in diameter represented below by the wire frames.
Charged particles in the magnetic field follow curved trajectories whose shapes indicate the particle momenta. The momenta of the particles are analyzed in many ways by about 200 STAR physicists. The UW group specializes in applying information theory and other statistical techniques to each event to search for subtle structures which can inform us about the process of nuclear melting and the process of reforming nuclear particles from the color-deconfined plasma. A significant analysis may involve 1 million events and a total data volume of about 1 Terabyte.