Relativistic Heavy Ion Collider
Encyclopedia
The Relativistic Heavy Ion Collider (RHIC, ˈ) is one of two existing heavy-ion
collider
s, and the only spin
-polarized proton
collider in the world. It is located at Brookhaven National Laboratory
(BNL) in Upton, New York
and operated by an international team of researchers. By using RHIC to collide ion
s traveling at relativistic
speeds, physicists study the primordial form of matter that existed in the universe
shortly after the Big Bang
. By colliding spin-polarized protons, the spin structure of the proton
is explored.
RHIC is now the second-highest-energy heavy-ion collider in the world. As of 7 November 2010, the LHC
has collided heavy ions of lead at higher energies than RHIC.
In 2010, RHIC physicists published results of temperature measurements from earlier experiments which concluded that temperatures in excess of 4 trillion kelvins (7 trillion degrees Fahrenheit) had been achieved in gold ion collisions, and that these collision temperatures resulted in the breakdown of "normal matter" and the creation of a liquid-like quark-gluon plasma
.
particle accelerator
. Two independent rings (arbitrarily denoted as "Blue" and "Yellow" rings, see also the photograph) circulate heavy ion
s and/or proton
s in opposite directions and allow a virtually free choice of colliding positively charged particle
s (the eRHIC upgrade will allow collisions between positively and negatively charged particles). The RHIC double storage ring is itself hexagonally shaped and long in circumference, with curved edges in which stored particles are deflected and focused by 1,740 superconducting niobium-titanium
magnet
s. The dipole magnet
s operate at . The six interaction points (between the particles circulating in the two rings) 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 near 6 o'clock. Two large experiments, STAR and PHENIX, are located at 6 and 8 o'clock respectively.
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 linear accelerator (Linac) is used. As an example, gold nuclei leaving the Tandem Van de Graaff have an energy of about per nucleon and have an electric charge Q = +31 (31 of 79 electrons stripped from the gold atom). The particles are then accelerated by the Booster Synchrotron to per nucleon, which injects the projectile now with Q = +77 into the Alternating Gradient Synchrotron
(AGS), before they finally reach 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).
The main types of particle combinations explored at RHIC are , , and . The projectiles typically travel at a speed of 99.995% of the speed of light
. For collisions, the center-of-mass
energy is typically (or per nucleon
); an average luminosity
of was targeted during the planning. The current average luminosity of the collider is , 10 times the design value. For polarized collision, Run-9 achieved center-of-mass energy of on 12 February 2009.
One unique characteristic of RHIC is its capability to produce polarized protons. RHIC holds the record of highest energy polarized protons. Polarized protons are injected into RHIC and preserve this state throughout the energy ramp. This is a difficult task that can only be accomplished with the aid of Siberian snakes (a chain of solenoid
s and quadrupole
s for aligning particles) and AC dipoles. The AC dipoles have been also used in non-linear machine diagnostics for the first time in RHIC.
There are four detectors at RHIC: STAR
(6 o'clock, and near the AGS-to-RHIC Transfer Line), PHENIX (8 o'clock), PHOBOS (10 o'clock), and BRAHMS (2 o'clock). Two of them are still active, with PHOBOS having completed its operation after 2005 and Run-05, and BRAHMS after 2006 and Run-06.
Among the two larger detectors, STAR
is aimed at the detection of hadron
s with its system of time projection chamber
s covering a large solid angle
and in a conventionally generated solenoidal magnetic field
, while PHENIX
is further specialized in detecting rare and electromagnetic particles, using a partial coverage detector system in a superconductively generated axial magnetic field. The smaller detectors have larger pseudorapidity coverage, PHOBOS has the largest pseudorapidity coverage of all detectors, and tailored for bulk particle multiplicity measurement, while BRAHMS is designed for momentum spectroscopy, in order to study the so called "small-x" and saturation physics. There is an additional experiment, PP2PP, investigating spin
dependence in p + p scattering
.
The spokespersons for each of the experiments are:
.
For the experimental objective of creating and studying the quark-gluon plasma, RHIC has the unique ability to provide baseline measurements for itself. This consists of the both lower energy and also lower mass number
projectile combinations that do not result in the density of 200 GeV Au + Au collisions, like the p + p and d + Au collisions of the earlier runs, and also Cu + Cu collisions in Run-5.
Using this approach, important results of the measurement of the hot QCD matter created at RHIC are:
While in the first years, theorists were eager to claim that RHIC has discovered the quark-gluon plasma (e.g. 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 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.
New results were published in Physical Review Letters
on February 16, 2010, stating the discovery of the first hints of symmetry transformations, and that the observations may suggest that bubbles formed in the aftermath of the collisions created in the RHIC may break parity symmetry
, which normally characterizes interactions
between quarks and gluons.
The RHIC physicists announced new temperature measurements for these experiments of up to 7.2 trillion kelvins, the highest temperature ever achieved in a laboratory. It is described as a recreation of the conditions that existed during the birth of the Universe.
of CERN
, while used mainly for colliding protons, will operate with heavy ions for about one month per year. LHC will eventually operate 28 times higher ion energies, although current LHC operation is at half this energy.
Due to the longer operating time per year, a greater number of colliding ion species and collision energies can be studied at RHIC. In addition and unlike the 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.
A planned major upgrade is eRHIC: The 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, then 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
.
such as creating a black hole
, a transition into a different quantum mechanical
vacuum
(see false vacuum
), or the creation of strange matter
that is more stable than ordinary matter
. These hypotheses are complex, but many predict that the Earth
would be destroyed in a time frame from seconds to millennia, depending on the theory considered. However, the fact that objects of the Solar System (e.g., the Moon
) have been bombarded with cosmic particles
of significantly higher energies than that of RHIC and other man made colliders for billions of years, without any harm to the Solar System, were among the most striking arguments that these hypotheses were unfounded.
The other main controversial issue was a demand by critics for physicist
s to reasonably exclude the probability
for such a catastrophic scenario. Physicists are unable to demonstrate experimental and astrophysical
constraints of zero probability of catastrophic events, nor that tomorrow Earth will be struck with a "doomsday
" cosmic ray
(they can only calculate an upper limit for the likelihood). The result would be the same destructive scenarios described above, although obviously not caused by humans. According to this argument of upper limits, RHIC would still modify the chance for the Earth's survival by an infinitesimal amount.
Concerns were raised in connection with the RHIC particle accelerator, both in the media and in the popular science media. The risk of a doomsday scenario was indicated by Martin Rees, with respect to the RHIC, as being at least a 1 in 50,000,000 chance. With regards to the production of strangelets, Frank Close
, professor of physics at the University of Oxford
, indicates that "the chance of this happening is like you winning the major prize on the lottery 3 weeks in succession; the problem is that people believe it is possible to win the lottery 3 weeks in succession." After detailed studies, scientists reached such conclusions as "beyond reasonable doubt, heavy-ion experiments at RHIC will not endanger our planet" and that there is "powerful empirical evidence against the possibility of dangerous strangelet production."
The debate started in 1999 with an exchange of letters in Scientific American
between Walter L. Wagner, 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 is similar mathematically. Therefore, RHIC collisions might be described by mathematics relevant to theories of quantum gravity
within AdS/CFT, but the described physical phenomena are not the same.
, 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:
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.
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
collider
Collider
A collider is a type of a particle accelerator involving directed beams of particles.Colliders may either be ring accelerators or linear accelerators.-Explanation:...
s, and the only spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
-polarized proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
collider in the world. It is located at Brookhaven National Laboratory
Brookhaven National Laboratory
Brookhaven National Laboratory , is a United States national laboratory located in Upton, New York on Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base...
(BNL) in Upton, New York
Upton, New York
Upton, New York is a hamlet on Long Island in the town of Brookhaven. It is the home of Brookhaven National Laboratory, and a National Weather Service station.Upton is located in Suffolk County, New York in the USA....
and operated by an international team of researchers. By using RHIC to collide ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s traveling at relativistic
Special relativity
Special relativity is the physical theory of measurement in an inertial frame of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".It generalizes Galileo's...
speeds, physicists study the primordial form of matter that existed in the universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
shortly after the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
. By colliding spin-polarized protons, the spin structure of the proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
is explored.
RHIC is now the second-highest-energy heavy-ion collider in the world. As of 7 November 2010, the LHC
LHC
LHC may refer to:* Large Hadron Collider, a particle accelerator and collider located on the Franco-Swiss border near Geneva, SwitzerlandLHC also may refer to:* La hora Chanante, a Spanish comedy television show...
has collided heavy ions of lead at higher energies than RHIC.
In 2010, RHIC physicists published results of temperature measurements from earlier experiments which concluded that temperatures in excess of 4 trillion kelvins (7 trillion degrees Fahrenheit) had been achieved in gold ion collisions, and that these collision temperatures resulted in the breakdown of "normal matter" and the creation of a liquid-like quark-gluon plasma
Quark-gluon plasma
A quark–gluon plasma or quark soup is a phase of quantum chromodynamics which exists at extremely high temperature and/or density. This phase consists of asymptotically free quarks and gluons, which are several of the basic building blocks of matter...
.
The accelerator
RHIC is an intersecting storage ringStorage ring
A storage ring is a type of circular particle accelerator in which a continuous or pulsed particle beam may be kept circulating for a long period of time, up to many hours. Storage of a particular particle depends upon the mass, energy and usually charge of the particle being stored...
particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
. Two independent rings (arbitrarily denoted as "Blue" and "Yellow" rings, see also the photograph) circulate heavy ion
Heavy ion
Heavy ion refers to an ionized atom which is usually heavier than helium. Heavy-ion physics is devoted to the study of extremely hot nuclear matter and the collective effects appearing in such systems, differing from particle physics, which studies the interactions between elementary particles...
s and/or proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s in opposite directions and allow a virtually free choice of colliding positively charged particle
Charged particle
In physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its...
s (the eRHIC upgrade will allow collisions between positively and negatively charged particles). The RHIC double storage ring is itself hexagonally shaped and long in circumference, with curved edges in which stored particles are deflected and focused by 1,740 superconducting niobium-titanium
Niobium-titanium
Niobium-titanium is an alloy of niobium and titanium, used industrially as a type II superconductor wire for superconducting magnets...
magnet
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
s. The dipole magnet
Dipole magnet
A dipole magnet, in particle accelerators, is a magnet constructed to create a homogeneous magnetic field over some distance. Particle motion in that field will be circular in a plane perpendicular to the field and collinear to the direction of particle motion and free in the direction orthogonal...
s operate at . The six interaction points (between the particles circulating in the two rings) 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 near 6 o'clock. Two large experiments, STAR and PHENIX, are located at 6 and 8 o'clock respectively.
Tandem
Tandem is an arrangement where a team of machines, animals or people are lined up one behind another, all facing in the same direction....
Van de Graaff
Van de Graaff generator
A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate very high voltages on a hollow metal globe on the top of the stand. It was invented in 1929 by American physicist Robert J. Van de Graaff. The potential differences achieved in modern Van de Graaff...
accelerator, while for protons, the linear accelerator (Linac) is used. As an example, gold nuclei leaving the Tandem Van de Graaff have an energy of about per nucleon and have an electric charge Q = +31 (31 of 79 electrons stripped from the gold atom). The particles are then accelerated by the Booster Synchrotron to per nucleon, which injects the projectile now with Q = +77 into the Alternating Gradient Synchrotron
Alternating Gradient Synchrotron
The Alternating Gradient Synchrotron is a particle accelerator located at the Brookhaven National Laboratory in Long Island, New York, USA....
(AGS), before they finally reach 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).
The main types of particle combinations explored at RHIC are , , and . The projectiles typically travel at a speed of 99.995% of the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
. For collisions, the center-of-mass
Center of mass
In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
energy is typically (or per nucleon
Nucleon
In physics, a nucleon is a collective name for two particles: the neutron and the proton. These are the two constituents of the atomic nucleus. Until the 1960s, the nucleons were thought to be elementary particles...
); an average luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
of was targeted during the planning. The current average luminosity of the collider is , 10 times the design value. For polarized collision, Run-9 achieved center-of-mass energy of on 12 February 2009.
One unique characteristic of RHIC is its capability to produce polarized protons. RHIC holds the record of highest energy polarized protons. Polarized protons are injected into RHIC and preserve this state throughout the energy ramp. This is a difficult task that can only be accomplished with the aid of Siberian snakes (a chain of solenoid
Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
s and quadrupole
Quadrupole magnet
Quadrupole magnets consist of groups of four magnets laid out so that in the multipole expansion of the field the dipole terms cancel and where the lowest significant terms in the field equations are quadrupole. Quadrupole magnets are useful as they create a magnetic field whose magnitude grows...
s for aligning particles) and AC dipoles. The AC dipoles have been also used in non-linear machine diagnostics for the first time in RHIC.
The experiments
STAR detector
The STAR detector is one of the four experiments at the Relativistic Heavy Ion Collider in Brookhaven National Laboratory, United States....
(6 o'clock, and near the AGS-to-RHIC Transfer Line), PHENIX (8 o'clock), PHOBOS (10 o'clock), and BRAHMS (2 o'clock). Two of them are still active, with PHOBOS having completed its operation after 2005 and Run-05, and BRAHMS after 2006 and Run-06.
Among the two larger detectors, STAR
STAR detector
The STAR detector is one of the four experiments at the Relativistic Heavy Ion Collider in Brookhaven National Laboratory, United States....
is aimed at the detection of hadron
Hadron
In particle physics, a hadron is a composite particle made of quarks held together by the strong force...
s with its system of time projection chamber
Time projection chamber
In physics, a time projection chamber is a particle detector invented by David R. Nygren, an American physicist, at Lawrence Berkeley Laboratory in the late 1970s...
s covering a large solid angle
Solid angle
The solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point...
and in a conventionally generated solenoidal magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
, while PHENIX
Phénix
Phénix was a small-scale prototype fast breeder reactor, located at the Marcoule nuclear site, near Orange, France. It was a pool-type liquid-metal fast breeder reactor cooled with liquid sodium...
is further specialized in detecting rare and electromagnetic particles, using a partial coverage detector system in a superconductively generated axial magnetic field. The smaller detectors have larger pseudorapidity coverage, PHOBOS has the largest pseudorapidity coverage of all detectors, and tailored for bulk particle multiplicity measurement, while BRAHMS is designed for momentum spectroscopy, in order to study the so called "small-x" and saturation physics. There is an additional experiment, PP2PP, investigating spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
dependence in p + p scattering
Scattering
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...
.
The spokespersons for each of the experiments are:
- STAR: Nu Xu (Lawrence Berkeley Laboratory, Nuclear Science Division)
- PHENIX: Barbara Jacak (Stony Brook University, Department of Physics and Astronomy)
- PHOBOS: Wit Busza (Massachusetts Institute of TechnologyMassachusetts Institute of TechnologyThe Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
Department of Physics and MIT Laboratory for Nuclear Science) - BRAHMS: Flemming Videbaek (Brookhaven National LaboratoryBrookhaven National LaboratoryBrookhaven National Laboratory , is a United States national laboratory located in Upton, New York on Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base...
, Physics Department) - PP2PP: Włodek Guryn (Brookhaven National LaboratoryBrookhaven National LaboratoryBrookhaven National Laboratory , is a United States national laboratory located in Upton, New York on Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base...
, Physics Department)
Current results
For a complementary discussion, see also quark-gluon plasmaQuark-gluon plasma
A quark–gluon plasma or quark soup is a phase of quantum chromodynamics which exists at extremely high temperature and/or density. This phase consists of asymptotically free quarks and gluons, which are several of the basic building blocks of matter...
.
For the experimental objective of creating and studying the quark-gluon plasma, RHIC has the unique ability to provide baseline measurements for itself. This consists of the both lower energy and also lower mass number
Mass number
The mass number , also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion...
projectile combinations that do not result in the density of 200 GeV Au + Au collisions, like the p + p and d + Au collisions of the earlier runs, and also Cu + Cu collisions in Run-5.
Using this approach, important results of the measurement of the hot QCD matter created at RHIC are:
- Collective anisotropy, or elliptic flowElliptic flowThe elliptic flow is described as one of the most important observations measured at the Relativistic Heavy Ion Collider . It is one of the strongest evidences for the Quark-gluon plasma discovery. It describes the azimuthal momentum space anisotropy of particle emission from non-central heavy-ion...
. The multiplicityMultiplicity (chemistry)Multiplicity in quantum chemistry is used to distinguish between several degenerate wavefunctions that differ only in the orientation of their angular spin momenta. It is defined as 2S+1, where S is the angular spin momentum....
of the particles' bulkBulk-Industry:* Bulk cargo* Bulk liquids* Bulk mail* Bulk material handling* Bulk pack, packaged bulk materials/products* Bulk purchasing- Physics :*Bulk density*Bulk modulus...
with lower momentaMomentumIn classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
exhibits a dependency as
(pT is the transverse momentum, 
angle with the reaction plane). This is a direct result of the elliptic shape of the nucleus overlap region during the collision and hydrodynamical property of the matter created.
- JetJet (particle physics)A jet is a narrow cone of hadrons and other particles produced by the hadronization of a quark or gluon in a particle physics or heavy ion experiment. Because of QCD confinement, particles carrying a color charge, such as quarks, cannot exist in free form. Therefore they fragment into hadrons...
quenching. In the heavy ion collision event, scattering with a high transverse pT can serve as a probe for the hot QCD matter, as it loses its energy while traveling through the medium. Experimentally, the quantity RAA (A is the mass number) being the quotient of observed jet yield in A + A collisions and Nbin × yield in p + p collisions shows a strong damping with increasing A, which is an indication of the new properties of the hot QCD matter created.
- Color glass condensateColor glass condensateThe color glass condensate is an extreme type of matter theorized to exist in atomic nuclei travelling near the speed of light.According to Einstein’s theory of relativity, a high-energy nucleus appears length contracted, or compressed, along its direction of motion...
saturationSaturation (chemistry)In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...
. The Balitsky–Fadin–Kuraev–Lipatov (BFKL) dynamics which are the result of a resummation of large logarithmic terms in Q² for deep inelastic scattering with small Bjorken-x, saturate at a unitarity limit
, with Npart/2 being the number of participant nucleons in a collision (as opposed to the number of binary collisions). The observed charged multiplicity follows the expected dependency of 
, supporting the predictions of the color glass condensateColor glass condensateThe color glass condensate is an extreme type of matter theorized to exist in atomic nuclei travelling near the speed of light.According to Einstein’s theory of relativity, a high-energy nucleus appears length contracted, or compressed, along its direction of motion...
model. For a detailed discussion, see e.g. Kharzeev et al.; for an overview of color glass condensates, see e.g. Iancu & Venugopalan.
- Particle ratios. The particle ratios predicted by statistical models allow the calculation of parameters such as the temperature at chemical freeze-out Tch and hadron chemical potential
. The experimental value Tch varies a bit with the model used, with most authors giving a value of 160 MeV < Tch < 180 MeV, which is very close to the expected QCD phase transition value of approximately 170 MeV obtained by lattice QCD calculations (see e.g. Karsch).
While in the first years, theorists were eager to claim that RHIC has discovered the quark-gluon plasma (e.g. 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 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.
New results were published in Physical Review Letters
Physical Review Letters
Physical Review Letters , established in 1958, is a peer reviewed, scientific journal that is published 52 times per year by the American Physical Society...
on February 16, 2010, stating the discovery of the first hints of symmetry transformations, and that the observations may suggest that bubbles formed in the aftermath of the collisions created in the RHIC may break parity symmetry
Parity (physics)
In physics, a parity transformation is the flip in the sign of one spatial coordinate. In three dimensions, it is also commonly described by the simultaneous flip in the sign of all three spatial coordinates:...
, which normally characterizes interactions
Color charge
In particle physics, color charge is a property of quarks and gluons that is related to the particles' strong interactions in the theory of quantum chromodynamics . Color charge has analogies with the notion of electric charge of particles, but because of the mathematical complications of QCD,...
between quarks and gluons.
The RHIC physicists announced new temperature measurements for these experiments of up to 7.2 trillion kelvins, the highest temperature ever achieved in a laboratory. It is described as a recreation of the conditions that existed during the birth of the Universe.
The future
RHIC began operation in 2000 and until November 2010 was the most powerful heavy-ion collider in the world. The Large Hadron Collider (LHC)Large Hadron Collider
The Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
of CERN
CERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
, while used mainly for colliding protons, will operate with heavy ions for about one month per year. LHC will eventually operate 28 times higher ion energies, although current LHC operation is at half this energy.
Due to the longer operating time per year, a greater number of colliding ion species and collision energies can be studied at RHIC. In addition and unlike the 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.
A planned major upgrade is eRHIC: The 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, then Interim Director of BNL, Sam Aronson, has contested the claim in a Physics Today
Physics Today
Physics Today, created in 1948, is the membership journal of the American Institute of Physics. It is provided to 130,000 members of twelve physics societies, including the American Physical Society...
report that "Tevatron
Tevatron
The Tevatron is a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory , just east of Batavia, Illinois, and is the second highest energy particle collider in the world after the Large Hadron Collider...
is unlikely to outlive the decade. Neither is ... the Relativistic Heavy Ion Collider", referring to a report of the National Research Council
United States National Research Council
The National Research Council of the USA is the working arm of the United States National Academies, carrying out most of the studies done in their names.The National Academies include:* National Academy of Sciences...
.
Critics of high energy experiments
Before RHIC started operation, critics postulated that the extremely high energy could produce catastrophic scenarios,such as creating a black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
, a transition into a different quantum mechanical
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
vacuum
Vacuum state
In quantum field theory, the vacuum state is the quantum state with the lowest possible energy. Generally, it contains no physical particles...
(see false vacuum
False vacuum
In quantum field theory, a false vacuum is a metastable sector of space that appears to be a perturbative vacuum, but is unstable due to instanton effects that may tunnel to a lower energy state. This tunneling can be caused by quantum fluctuations or the creation of high-energy particles...
), or the creation of strange matter
Strange matter
Strange matter is a particular form of quark matter, usually thought of as a "liquid" of up, down, and strange quarks. It is to be contrasted with nuclear matter, which is a liquid of neutrons and protons , and with non-strange quark matter, which is a quark liquid containing only up and down quarks...
that is more stable than ordinary matter
Matter
Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...
. These hypotheses are complex, but many predict that the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
would be destroyed in a time frame from seconds to millennia, depending on the theory considered. However, the fact that objects of the Solar System (e.g., the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
) have been bombarded with cosmic particles
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
of significantly higher energies than that of RHIC and other man made colliders for billions of years, without any harm to the Solar System, were among the most striking arguments that these hypotheses were unfounded.
The other main controversial issue was a demand by critics for physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
s to reasonably exclude the probability
Probability
Probability is ordinarily used to describe an attitude of mind towards some proposition of whose truth we arenot certain. The proposition of interest is usually of the form "Will a specific event occur?" The attitude of mind is of the form "How certain are we that the event will occur?" The...
for such a catastrophic scenario. Physicists are unable to demonstrate experimental and astrophysical
Astrophysics
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...
constraints of zero probability of catastrophic events, nor that tomorrow Earth will be struck with a "doomsday
Doomsday event
A doomsday event is a specific, plausibly verifiable or hypothetical occurrence which has an exceptionally destructive effect on the human race...
" cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
(they can only calculate an upper limit for the likelihood). The result would be the same destructive scenarios described above, although obviously not caused by humans. According to this argument of upper limits, RHIC would still modify the chance for the Earth's survival by an infinitesimal amount.
Concerns were raised in connection with the RHIC particle accelerator, both in the media and in the popular science media. The risk of a doomsday scenario was indicated by Martin Rees, with respect to the RHIC, as being at least a 1 in 50,000,000 chance. With regards to the production of strangelets, Frank Close
Frank Close
Francis Edwin Close OBE is a noted particle physicist who is currently Professor of Physics at the University of Oxford and a Fellow of Exeter College, Oxford.-Early life:...
, professor of physics at the University of Oxford
University of Oxford
The University of Oxford is a university located in Oxford, United Kingdom. It is the second-oldest surviving university in the world and the oldest in the English-speaking world. Although its exact date of foundation is unclear, there is evidence of teaching as far back as 1096...
, indicates that "the chance of this happening is like you winning the major prize on the lottery 3 weeks in succession; the problem is that people believe it is possible to win the lottery 3 weeks in succession." After detailed studies, scientists reached such conclusions as "beyond reasonable doubt, heavy-ion experiments at RHIC will not endanger our planet" and that there is "powerful empirical evidence against the possibility of dangerous strangelet production."
The debate started in 1999 with an exchange of letters in Scientific American
Scientific American
Scientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...
between Walter L. Wagner, and F. Wilczek
Frank Wilczek
Frank Anthony Wilczek is a theoretical physicist from the United States and a Nobel laureate. He is currently the Herman Feshbach Professor of Physics at the Massachusetts Institute of Technology ....
, Institute for Advanced Study
Institute for Advanced Study
The Institute for Advanced Study, located in Princeton, New Jersey, United States, is an independent postgraduate center for theoretical research and intellectual inquiry. It was founded in 1930 by Abraham Flexner...
, in response to a previous article by M. Mukerjee. The media attention unfolded with an article in U.K.
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
Sunday Times
The Sunday Times (UK)
The Sunday Times is a Sunday broadsheet newspaper, distributed in the United Kingdom. The Sunday Times is published by Times Newspapers Ltd, a subsidiary of News International, which is in turn owned by News Corporation. Times Newspapers also owns The Times, but the two papers were founded...
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
Committee
A committee is a type of small deliberative assembly that is usually intended to remain subordinate to another, larger deliberative assembly—which when organized so that action on committee requires a vote by all its entitled members, is called the "Committee of the Whole"...
convened by the director
Board of directors
A board of directors is a body of elected or appointed members who jointly oversee the activities of a company or organization. Other names include board of governors, board of managers, board of regents, board of trustees, and board of visitors...
of Brookhaven National Laboratory, J. H. Marburger
John Marburger
John Harmen Marburger, III was an American physicist who directed the Office of Science and Technology Policy in the administration of President George W. Bush, thus serving as the Science Advisor to the President...
, 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
Federal government of the United States
The federal government of the United States is the national government of the constitutional republic of fifty states that is the United States of America. The federal government comprises three distinct branches of government: a legislative, an executive and a judiciary. These branches and...
lawsuits in San Francisco and New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
, 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
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
published an article implying that researcher Horaţiu Năstase
Horatiu Nastase
Horaţiu Năstase is a Romanian physicist and professor in the String Theory group at Instituto de Física Teórica of the Universidade Estadual Paulista in São Paulo, Brazil....
believes black holes have been created at RHIC. However, the original papers of H. Năstase and the New Scientist
New Scientist
New Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...
article cited by the BBC state that the correspondence of the hot dense QCD matter
QCD matter
Quark matter or QCD matter refers to any of a number of theorized phases of matter whose degrees of freedom include quarks and gluons. These theoretical phases would occur at extremely high temperatures and densities, billions of times higher than can be produced in equilibrium in laboratories...
created in RHIC to a black hole is only in the sense of a correspondence of QCD
Quantum chromodynamics
In theoretical physics, quantum chromodynamics is a theory of the strong interaction , a fundamental force describing the interactions of the quarks and gluons making up hadrons . It is the study of the SU Yang–Mills theory of color-charged fermions...
scattering in Minkowski space
Minkowski space
In physics and mathematics, Minkowski space or Minkowski spacetime is the mathematical setting in which Einstein's theory of special relativity is most conveniently formulated...
and scattering in the AdS5 × X5 space in AdS/CFT; in other words, it is similar mathematically. Therefore, RHIC collisions might be described by mathematics relevant to theories of quantum gravity
Quantum gravity
Quantum gravity is the field of theoretical physics which attempts to develop scientific models that unify quantum mechanics with general relativity...
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 EnergyUnited States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
, Office of Science
Science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...
, Office of Nuclear Physics
Nuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
. 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
Renaissance Technologies
Renaissance Technologies is a hedge fund management company of about 275 employees and more than $ billion in assets under management in three funds...
of East Setauket, New York.
RHIC in fiction
- The novel Cosm (ISBN 0-380-79052-1) by the American author Gregory BenfordGregory BenfordGregory Benford is an American science fiction author and astrophysicist who is on the faculty of the Department of Physics and Astronomy at the University of California, Irvine...
takes place at RHIC. The science fictionScience fictionScience fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...
setting describes the main character Alicia Butterworth, a physicist at the BRAHMS experiment, and a new universeUniverseThe Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
being created in RHIC by accident, while running with uraniumUraniumUranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
ions.
- The zombie apocalypseZombie apocalypseA zombie apocalypse is a particular scenario of apocalyptic literature that customarily has a science fiction/horror rationale. In a zombie apocalypse, a widespread rise of zombies hostile to human life engages in a general assault on civilization....
novel The Rising by the American author Brian KeeneBrian KeeneBrian Keene is an American author, primarily of horror, crime fiction, and comic books. He has won two Bram Stoker Awards.- Background :Keene was born in 1967. He grew up in both Pennsylvania and West Virginia, and many of his books take place in these locales. After graduating high school, he...
referenced the media concerns of activating the RHIC raised by the article in The Sunday TimesThe Sunday Times (UK)The Sunday Times is a Sunday broadsheet newspaper, distributed in the United Kingdom. The Sunday Times is published by Times Newspapers Ltd, a subsidiary of News International, which is in turn owned by News Corporation. Times Newspapers also owns The Times, but the two papers were founded...
of July 18, 1999 by J. Leake,. As revealed very early in the story, side effects of the collider experiments of the RHIC (located at "Havenbrook National Laboratories") were the cause of the zombie uprising in the novel and its sequel City of the DeadCity of the Dead (novel)City of the Dead by Brian Keene was first published in 2005. It is the sequel to The Rising.-Plot summary:Jim finds Danny alive as the book opens but the living dead soon converge on their location. Frankie and Martin join Jim in the house and they are soon trapped in the attic. As they see...
.