Relativistic Heavy Ion Collider

The Relativistic Heavy Ion Collider (RHIC) is a heavy-ion collider located at and operated by the Brookhaven National Laboratory in Upton, New York. It is sponsored by the U.S. Department of Energy Office of Science, Office of Nuclear Physics. The RHIC project had a line-item budget of 616.6 million US dollar.

Main types of projectile combinations used at RHIC are: p + p, d + Au and Au + Au. The projectiles typically travel at a speed of 99.995% of the speed of light in vacuum. For Au + Au collision, the center-of-mass energy ${\sqrt {s}}$ is 200 GeV per nucleon (or 100 GeV per nucleon for each projectile), and a luminosity of 2 × 10²⁶ cm^-2 s^-1 was targeted during the planning. The current luminosity performance of the collider is 2.96 × 10²⁶ cm^-2 s^-1 (Run-4/PHENIX).

The RHIC double storage ring is itself hexagonally shaped and 3834 m long in circumference, with curved edges in which stored projectiles are deflected by 1,740 superconducting niobium titanium magnets. The 6 interaction points are at the middle of the 6 relatively straight sections, where the two rings crosses, allowing the projectiles to collide. The interaction points are enumerated by clock positions, with the injection point at "6 o'clock". 2 interaction points are unused and left for further expansion.

A projectiles passes several stages of boosters, before it reaches the RHIC storage ring. The first stage for ions is the Tandem Van de Graaff accelerator, while for protons, the 200 MeV linear accelerator (Linac) is used. As an example, Au nucleus leaving the Tandem Van de Graaff have a energy of about 1 MeV per nucleon and have Q = +32 (32 electrons stripped from the Au atom). The projectiles then are continued to be accelerated by the Booster Synchrotron to 95 MeV per nucleon, which injects the projectile now with Q = +77 into the Alternating Gradient Synchrontron (AGS), before they finally reach 8.86 GeV per nucleon and are injected in a Q = +79 state (no electrons left) into the RHIC storage ring over the AGS-To-RHIC Transfer Line (ATR), sitting at the 6 o'clock position, near the STAR detector.

RHIC consists of four detectors: STAR (6 o'clock), PHENIX (8 o'clock), PHOBOS (10 o'clock), and BRAHMS (2 o'clock). While the main objective of the two bigger detectors PHENIX and STAR, and also PHOBOS are the experimental detection and study of quark-gluon plasma, BRAHMS is mainly interested in the so called "small-x physics". There is a further experiment PP2PP, investigating spin dependence in p + p scattering.

The spokespersons for each of the experiments are:

STAR: Timothy Hallman (Brookhaven National Laboratory, Physics Department)
PHENIX: William A. Zajc (Columbia University, Department of Physics and Nevis Laboratories)
PHOBOS: Wit Busza (Massachusetts Institute of Technology Department of Physics and MIT Laboratory for Nuclear Science)
BRAHMS: Flemming Videbaek (Brookhaven National Laboratory, Physics Department)
PP2PP: Włodek Guryn (Brookhaven National Laboratory, Physics Department)

RHIC began its operation in 2000 and is currently the strongest heavy-ion collider in the world. It is expected, however, that the Large Hadron Collider of the Centre Européenne pour la Recherche Nucléaire (CERN) will provide significantly higher energy once completed, essentially superseding RHIC.

A recent overview of the physics result is provided by Adcox, et al. (2004), a community-wide effort of RHIC experiments to evaluate the current data in the context of implication for formation of a new state of matter. These results are from the first three years of data collections at the RHIC.

Fears among the Public

Before RHIC started its operation, there has been fears among the public, that the extremely high energy could produce one of the following catastrophic scenarios:

RHIC creates a black hole
RHIC creates a transition into a different quantum mechanical vacuum
RHIC creates strange matter that is more stable than ordinary matter

The detail of those hypothetic theories are complex, but they predict that at least the Earth and the Solar System would be destroyed within few seconds. However, the fact that objects of the Solar System (e.g. the Moon) are bombarded with cosmic particles of significantly higher energies than that of RHIC for billion of years, without any harm to the Solar System, are among the most strking arguments that these hypotheses were unfounded.

Fears among the Public

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