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.
The Accelerator
RHIC is an intersecting storage ring (ISR) accelerator. 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 (also refer the RHIC Complex diagram).
Main types of projectile combinations used at RHIC are: p + p, d + Au,
Cu + Cu 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 
is currently up to 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).
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.
The Experiments
RHIC consists of four detectors: STAR (6 o'clock and near the ATR), 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" and saturation physics. There is a further experiment PP2PP, investigating spin dependence in p + p scattering.
The spokespersons for each of the experiments are:
Current Results
While theorists are more eager to claim RHIC having discovered the quark-gluon plasma (e.g. Gyulassy & McLarren, 2004), the experimental groups are more careful to jump to a conclusion, citing various variables still in need of further measurement. A recent overview of the physics result is e.g. provided by Adcox, et al. (2004), part of the RHIC Experimental Evaluations 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.
The Future
RHIC began its operation in 2000 and is currently the most powerful heavy-ion collider in the world. It is expected, however, that the Large Hadron Collider of the Conseil Européenne pour la Recherche Nucléaire (CERN) will provide significantly higher energy once completed, essentially superseding RHIC. It is expected, however, that RHIC will remain unique in various fields that Large Hadron Collider will not be able to cover, like tomographic study of quark-gluon plasma, spin physics and saturation physics. Two planned upgrades should enhance the future scientific output of RHIC in these fields:
- RHIC-II: An upgrade that increase the luminosity by a further factor 10, together with upgrades to the detectors STAR and PHENIX.
- eRHIC: Construction of a 20 GeV electron storage ring together with a specialized eRHIC detector, allowing electron-ion collisions.
Fears among the public
Before RHIC started its operation, there have been fears among the public, that the extremely high energy could produce one of the following catastrophic scenarios:
The hypothetical 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, were among the most strking arguments that these hypotheses were unfounded.
The other main issue in the controversy is the demand by the critics of RHIC to physicists to show an exactly zero probability for such a catastrophic scenario, which the physics cannot provide. However, by following the same argument of the critics, and using the same experimental and astrophysical constraints, the phyiscs is also not able to demonstrate a zero probability, but just a upper limit for the likelihood that tomorrow Earth will be striken with a "doomsday" cosmic ray, resulting in the same destructive scenarios. By choosing the standpoint to argue with upper limits, RHIC would still modify the chance for the Earth's survival by a extremely marginal amount.
The debate started in 1999 with an exchange of letters in Scientific American between W. L. Wagner, World Botanical Gardens, Inc. and F. Wilczek, Institute for Advanced Study to an previous article by M. Mukerjee (1999) in Scientific American. The media attention unfolded with the article in U.K. Sunday Times of July 18, 1999 by J. Leake [1], closely followed by the U.S. media. The controversy mostly ended with the report of a committee convened by the director of Brookhaven National Laboratory, J. H. Marburger, ruling out the catastrophic scenarios depited (R. Jaffe et al., 2000). W. L. Wagner tried subsequently – as he attempted with various accelerators before – to stop full energy collision at RHIC by filing federal lawsuits in San Francisco and New York, but without success (see e.g. [2]).
On March 17, 2005, the BBC reported that researcher Horatiu Nastase believes this has indeed occurred. [3] However, the report is very likely to be the product of the journalist's misconception. Both the original papers of H. Nastase [4] and the New Scientist article [5] cited by the BBC states that the correspondence of the hot dense QCD matter created in RHIC to a black hole is only in the sense of a correspondence of QCD scattering in Minkowski space and scattering in the AdS5 × X5 space in AdS/CFT. RHIC collisions therefore might be useful to study various quantum gravity behaviors within the AdS/CFT, but the described physical phenomena are not the same.
RHIC in the Fictional Literature
The novel "Cosm" by the american author Gregory Benford takes place at RHIC. The science fiction setting describes the main character Alicia Butterworth, a physicist at the BRAHMS experiment, and a new universe being created in RHIC by accident, while running with Uranium ions (see [6], page 2).
References
- K. D. Adcox, et al., "Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration", nucl-ex/0410003 (2004), to be submitted to Nucl. Phys. A.
- K. Filimonov, for the STAR Collaboration, "Overview of results from the STAR experiment at RHIC", Report LBNL-53085 (2003).
- M. Gyulassy & L. McLerran, "New Forms of QCD Matter Discovered at RHIC", nucl-th/0405013 (2004), accepted by Nucl. Phys. A.
- M. Harrison, T. Ludlam, & S. Ozaki (Eds.), Nucl. Instr. Meth. Phys. Res. A 499(2–3), 235–880 (2003).
- R. Jaffe, et al., "Review of Speculative 'Disaster Scenarios' at RHIC", Rev. Mod. Phys. 72, 1125–1140 (2000).
- T. Ludlam & L. McLerran, "What Have We Learned From the Relativistic Heavy Ion Collider?", Phys. Today October 2003.
- K. McNulty Walsh, "Latest RHIC Results Make News Headlines at Quark Matter 2004", Discover Brookhaven 2(1), 14–17 (2004).
- M. Mukerjee, "A little big-bang", Scientific American 280(March), 60–66 (1999).
- W.A. Zajc, for the PHENIX Collaboration, "Overview of PHENIX Results from the First RHIC Run", Nucl. Phys. A 698, 39–53 (2002).
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