Relativistic Heavy Ion Collider Totally Explained

Everything about The Relativistic Heavy Ion Collider totally explained

The Relativistic Heavy Ion Collider (RHIC, pronounced like "rick", ) is a heavy-ion collider located at and operated by Brookhaven National Laboratory (BNL) in Upton, New York. By using RHIC to collide ions traveling at relativistic speeds, physicists study the primordial form of matter that existed in the universe shortly after the Big Bang, and also the structure of protons.
At present, RHIC is the most powerful heavy-ion collider in the world. It is also distinctive in its capability to collide spin-polarized protons.

The accelerator

RHIC is an intersecting storage ring (ISR) particle accelerator. Two independent rings (arbitrarily denoted as "blue" and "yellow" rings, see also the photograph) allow a virtually free choice of colliding projectiles. The RHIC double storage ring is itself hexagonally shaped and 3834 m long in circumference, with curved edges in which stored particles are deflected by 1,740 superconducting niobium titanium magnets. The six interaction points are at the middle of the six relatively straight sections, where the two rings cross, allowing the particles to collide. The interaction points are enumerated by clock positions, with the injection point at 6 o'clock. Two interaction points are unused and left for further expansion (refer also to the RHIC Complex diagram

).
A particle passes through 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, gold nuclei leaving the Tandem Van de Graaff have an energy of about 1 MeV per nucleon and have an electric charge Q = +32 (32 electrons stripped from the gold atom). The particles are then accelerated by the Booster Synchrotron to 95 MeV per nucleon, which injects the projectile now with Q = +77 into the Alternating Gradient Synchrotron (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 main types of particle 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

sqrt/A propto 1/alpha_s(Q_s^2)

, supporting the predictions of the color glass condensate model. For a detailed discussion, see for example Kharzeev et al.; for an overview of color glass condensates, see for example Iancu & Venugopalan.

Particle ratios. The particle ratios predicted by statistical models allow the calculation of parameters such as the temperature at chemical freeze-out T_ch and hadron chemical potential

mu_B

. The experimental value T_ch varies a bit with the model used, with most authors giving a value of 160 MeV < T_ch < 180 MeV, which is very close to the expected QCD phase transition value of approximately 170 MeV obtained by lattice QCD calculations (see for example Karsch). While in the first years, theorists were eager to claim that RHIC has discovered the quark-gluon plasma (for example Gyulassy & McLarren), though the experimental groups were more careful not to jump to conclusions, citing various variables still in need of further measurement. The present results shows that the matter created is a fluid with a viscosity near the quantum limit, but is unlike a weakly interacting plasma (a widespread yet not quantitatively unfounded belief on how quark gluon plasma looks).
A recent overview of the physics result is for example provided by 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 collection at RHIC.

The future

RHIC began operation in 2000 and is currently the most powerful heavy-ion collider in the world. It is expected, however, that the Large Hadron Collider (LHC) of CERN will provide significantly higher energies once completed, essentially superseding RHIC.
However, RHIC will likely remain unique in various fields that the LHC in the present state won't be able to cover. Unlike LHC, RHIC is able to accelerate spin polarized protons, which would leave RHIC as the world's highest energy accelerator for studying spin-polarized proton structure. And ALICE, the dedicated heavy ion detector at LHC, unlike STAR and PHENIX, lacks a calorimeter for jet tomographic studies. As a result, heavy ion studies with the hadronic detectors of LHC has been proposed, also a calorimeter upgrade with partial angular coverage has been proposed for ALICE.
Two planned upgrades should enhance the future scientific output of RHIC in these areas:

RHIC-II: An upgrade that will increase the luminosity by a further factor of 10, together with upgrades to the detectors STAR and PHENIX.

eRHIC: Construction of a 10 GeV high intensity electron/positron beam facility, allowing electron-ion collisions. At least one new detector will have to be built to study the collisions. A recent review is given by A. Deshpande et al.. In October 2006, the Interim Director of BNL, Sam Aronson has contested the claim in a Physics Today report that "Tevatron is unlikely to outlive the decade. Neither is ... the Relativistic Heavy Ion Collider", referring to a report of the National Research Council.

Fears among the public

Before RHIC started operation, there were 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 (see false vacuum)

RHIC creates strange matter that's more stable than ordinary matter These hypothetical theories are complex, but they predict that at least the Earth would be destroyed within seconds, to years, to millenia, depending on the theories. However, the fact that objects of the Solar System (for example, the Moon) have been bombarded with cosmic particles of significantly higher energies than that of RHIC for billions of years, without any harm to the Solar System, were among the most striking arguments that these hypotheses were unfounded., and F. Wilczek, Institute for Advanced Study, in response to a previous article by M. Mukerjee. The media attention unfolded with an article in U.K. Sunday Times of July 18, 1999 by J. Leake, closely followed by articles in 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, ostensibly ruling out the catastrophic scenarios depicted. However, the report left open the possibility that relativistic cosmic ray impact products might behave differently while transiting earth compared to "at rest" RHIC products; and the possibility that the qualitative difference between high-E proton collisions with earth or the moon might be different than Gold on Gold collisions at the RHIC. Wagner tried subsequently to stop full energy collision at RHIC by filing Federal lawsuits in San Francisco and New York, but without success.. The New York suit was dismissed on the technicality that the San Francisco suit was the preferred forum. The San Francisco suit was dismissed, but with leave to refile if additional information was developed and presented to the court.
On March 17, 2005, the BBC published an article implying that researcher Horaţiu Năstase believes black holes have been created at RHIC. However, the original papers of H. Năstase and the New Scientist article cited by the BBC state 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; in other words, it's similar mathematically. Therefore, RHIC collisions might be useful to study quantum gravity behavior within AdS/CFT, but the described physical phenomena are not the same.

Financial Information

The RHIC project is sponsored by the United States Department of Energy, Office of Science, Office of Nuclear Physics. It had a line-item budget of 616.6 million U.S. dollars. The annual operational budgets were:

fiscal year 2005: 131.6 million U.S. dollars

fiscal year 2006: 115.5 million U.S. dollars

fiscal year 2007, requested: 143.3 million U.S. dollars The total investment by 2005 is approximately 1.1 billion U.S. dollars. Though operation under the fiscal year 2006 federal budget cut was uncertain, a key portion of the operational cost (13 million U.S. dollars) was contributed privately by a group close to Renaissance Technologies of East Setauket, New York.

RHIC in fiction

The novel Cosm (ISBN 0-380-79052-1) 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.

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