Relativistic nuclear collisions
Encyclopedia
When atomic nuclei, generally called heavy-ions,
collide at very high energies, such that the
kinetic energy
exceeds significantly the rest mass energy,
many strongly interacting particles
are produced. We refer to these
reactions as (ultra)relativistic heavy-ion, or nuclear, collisions.
The energy density
with which we are
concerned has a benchmark value of
.
The corresponding relativistic matter pressure
is
The
theoretical work on multiparticle
production by Enrico Fermi
in the USA, and Lev Landau
in the USSR paved the way to the development
in the early sixties of the statistical bootstrap model description of hadron
production by Rolf Hagedorn
.
The multiparticle production
work was primarily the domain of particle physics
However, since the early seventies interest in nuclear
`heavy-ion' (often not fully stripped heavy atoms)
collision experiments at
relativistic energies had been growing within the
nuclear physics
community. The initial experimental program
was launched at the Lawrence Berkeley National Laboratory
, LBNL,
at Berkeley
, USA, and at the Joint Institute for Nuclear Research,
JINR, in Dubna, USSR.
At the LBL, a transport line was built to carry heavy ions from
the heavy ion accelerator HILAC to
the Bevatron
which was made famous by the discovery of antiprotons
in the early fifties. This new BEVALAC facility
permitted the acceleration of nuclear projectiles to
about 1 A GeV/c. Lighter projectiles, which could be
completely ionized and had more favorable
charge over mass ratios, were
accelerated to above 2 A GeV
/c . At the JINR in Dubna,
a similar program of research with an acceleration capability
restricted to lighter ions has been developed.
More recently, another heavy-ion accelerator complex, the SIS
(Schwer\-IonenSynchrotron), of comparable energy to BEVELAC, has been erected at
the Gesellschaft für Schwerionenforschung
laboratory, GSI, in Darmstadt
,
Germany. About the time the more modern SIS started up,
the BEVELAC closed down in 1993.
The beam
energy or momentum in relativistic heavy ions collisions is presented per nucleon (proton or neutron)
present in the nucleus being considered. thus: 200 A GeV . implies
a projectile with the total energy 200 A GeV, or
momentum 200 A GeV/c , where A is the number of nucleons in
the projectile. Scientists rarely differentiate between the
units of mass GeV/c^2, of momentum GeV/c, and of energy GeV,
in the relativistic domain of interest. This corresponds to the commonly used convention which sets
the units of time such that c=1.
The energy scale at the level of 1-2 GeV per nucleon yields compressed nuclear
matter at few times normal nuclear density, and yields final-state particle (spectral) `temperatures'
at or below 100 MeV, conditions which are generally considered
inadequate for study of when the elementary quarks and gluons
begin to roam freely and are deconfined
in the reaction volume.
The success of the initial-heavy ion experimental
program, specifically the demonstration of the possibility of
studying the properties of compressed and excited nuclear matter, gave
birth to the research programs at much higher energies available at BNL
and CERN
. Much of
this interest has been driven by the hope and expectation that,
within the reach of existing elementary-particle-accelerator facilities,
one may find the point of transition to the new QGP phase.
The first oxygen
beam at 60 A GeV was
extracted from the Super Proton Synchrotron (SPS
)
accelerator at CERN and met the target in the late autumn of
1986, about the same time as the BNL started its experimental
program at the Alternate Gradient Synchrotron (AGS
) accelerator
with a 15 A GeV silicon
-ion beam. Very soon thereafter, the energy of
the SPS beam could be increased to 200 A GeV and a sulfur
-ion
source was added. In order to study the relatively large volumes
and longer lifetimes expected in dense matter formed in collisions
of the heaviest nuclei, an upgrade of the SPS injector system was
approved, which, as of 1994, allowed to accelerate lead (Pb
) ions
to 158 A GeV. At the BNL, a gold (Au
)-ion beam with energy up to
11 A GeV became available at that time. The smaller beam energy per nucleon of the heavier Pb ions compared
with that for sulfur
reflects their smaller ratio of particle charge to
particle mass, given a fixed magnetic field strength
used to bend the beam into a circular orbit in an accelerator.
At the BNL, the Relativistic Heavy Ion Collider (RHIC), was completed
in 1999 and it allowed the study of colliding nuclear beams at up
to 100 A GeV. This new energy domain achieved with colliding beams
has extended the reach of experiments considerably. in 2008 the Large Hadron
Collider (LHC
) set in the 27-km CERN-LEP tunnel was inaugurated. It comprises an
important heavy-ion program at energies about a factor of 30 greater
than those of the RHIC. heavy Ion data from the LHC will become available in 2010.
collide at very high energies, such that the
kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
exceeds significantly the rest mass energy,
many strongly interacting particles
Hadron
In particle physics, a hadron is a composite particle made of quarks held together by the strong force...
are produced. We refer to these
reactions as (ultra)relativistic heavy-ion, or nuclear, collisions.
The energy density
Energy density
Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
with which we are
concerned has a benchmark value of
.The corresponding relativistic matter pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
is
The
theoretical work on multiparticle
production by Enrico Fermi
Enrico Fermi
Enrico Fermi was an Italian-born, naturalized American physicist particularly known for his work on the development of the first nuclear reactor, Chicago Pile-1, and for his contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics...
in the USA, and Lev Landau
Lev Landau
Lev Davidovich Landau was a prominent Soviet physicist who made fundamental contributions to many areas of theoretical physics...
in the USSR paved the way to the development
in the early sixties of the statistical bootstrap model description of hadron
Hadron
In particle physics, a hadron is a composite particle made of quarks held together by the strong force...
production by Rolf Hagedorn
Rolf Hagedorn
Rolf Hagedorn was a German theoretical physicists working at CERN. He is known for the idea that hadronic matter has a "melting point". The Hagedorn temperature is named in his honor.-Early life:...
.
The multiparticle production
work was primarily the domain of particle physics
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
However, since the early seventies interest in nuclear
`heavy-ion' (often not fully stripped heavy atoms)
collision experiments at
relativistic energies had been growing within the
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...
community. The initial experimental program
was launched at the Lawrence Berkeley National Laboratory
Lawrence Berkeley National Laboratory
The Lawrence Berkeley National Laboratory , is a U.S. Department of Energy national laboratory conducting unclassified scientific research. It is located on the grounds of the University of California, Berkeley, in the Berkeley Hills above the central campus...
, LBNL,
at Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
, USA, and at the Joint Institute for Nuclear Research,
JINR, in Dubna, USSR.
At the LBL, a transport line was built to carry heavy ions from
the heavy ion accelerator HILAC to
the Bevatron
Bevatron
The Bevatron was a historic particle accelerator — specifically, a weak-focusing proton synchrotron — at Lawrence Berkeley National Laboratory, U.S.A., which began operating in 1954. The antiproton was discovered there in 1955, resulting in the 1959 Nobel Prize in physics for Emilio...
which was made famous by the discovery of antiprotons
in the early fifties. This new BEVALAC facility
permitted the acceleration of nuclear projectiles to
about 1 A GeV/c. Lighter projectiles, which could be
completely ionized and had more favorable
charge over mass ratios, were
accelerated to above 2 A GeV
GEV
GEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
/c . At the JINR in Dubna,
a similar program of research with an acceleration capability
restricted to lighter ions has been developed.
More recently, another heavy-ion accelerator complex, the SIS
Sis
- Places :* Sis * Sis, Armenia, a town* Sis, Azerbaijan, a village* Sis, Iran, a city* Kozan, Adana, Sis in Armenian* Mountains of Sis, a range of the Pre-Pyrenees- Other :...
(Schwer\-IonenSynchrotron), of comparable energy to BEVELAC, has been erected at
the Gesellschaft für Schwerionenforschung
Gesellschaft für Schwerionenforschung
The GSI Helmholtz Centre for Heavy Ion Research GmbH in the Wixhausen suburb of Darmstadt, Germany is a federally and state co-funded heavy ion research center. The current director of GSI is Horst Stöcker who succeeded Walter F...
laboratory, GSI, in Darmstadt
Darmstadt
Darmstadt is a city in the Bundesland of Hesse in Germany, located in the southern part of the Rhine Main Area.The sandy soils in the Darmstadt area, ill-suited for agriculture in times before industrial fertilisation, prevented any larger settlement from developing, until the city became the seat...
,
Germany. About the time the more modern SIS started up,
the BEVELAC closed down in 1993.
The beam
energy or momentum in relativistic heavy ions collisions is presented per nucleon (proton or neutron)
present in the nucleus being considered. thus: 200 A GeV . implies
a projectile with the total energy 200 A GeV, or
momentum 200 A GeV/c , where A is the number of nucleons in
the projectile. Scientists rarely differentiate between the
units of mass GeV/c^2, of momentum GeV/c, and of energy GeV,
in the relativistic domain of interest. This corresponds to the commonly used convention which sets
the units of time such that c=1.
The energy scale at the level of 1-2 GeV per nucleon yields compressed nuclear
matter at few times normal nuclear density, and yields final-state particle (spectral) `temperatures'
at or below 100 MeV, conditions which are generally considered
inadequate for study of when the elementary quarks and gluons
begin to roam freely and are deconfined
Deconfinement
In physics, deconfinement is the property of a phase in which certain particles are allowed to exist as free excitations, rather than only within bound states...
in the reaction volume.
The success of the initial-heavy ion experimental
program, specifically the demonstration of the possibility of
studying the properties of compressed and excited nuclear matter, gave
birth to the research programs at much higher energies available at BNL
BNL
BNL may refer to:* Barenaked Ladies, a rock band from Canada* Banca Nazionale del Lavoro, an Italian bank* Block nested loop, an algorithm used to join data in a relational database* British National League, a defunct ice hockey league...
and 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...
. Much of
this interest has been driven by the hope and expectation that,
within the reach of existing elementary-particle-accelerator facilities,
one may find the point of transition to the new QGP phase.
The first oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
beam at 60 A GeV was
extracted from the Super Proton Synchrotron (SPS
SPS
The abbreviation SPS stands for items in the following categories:-Computer and gaming hardware and software:*SharePoint Portal Server, a Microsoft Office product*Sleep Proxy Service, a power management enhancement to Multicast DNS...
)
accelerator at CERN and met the target in the late autumn of
1986, about the same time as the BNL started its experimental
program at the Alternate Gradient Synchrotron (AGS
Alternating Gradient Synchrotron
The Alternating Gradient Synchrotron is a particle accelerator located at the Brookhaven National Laboratory in Long Island, New York, USA....
) accelerator
with a 15 A GeV silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
-ion beam. Very soon thereafter, the energy of
the SPS beam could be increased to 200 A GeV and a sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
-ion
source was added. In order to study the relatively large volumes
and longer lifetimes expected in dense matter formed in collisions
of the heaviest nuclei, an upgrade of the SPS injector system was
approved, which, as of 1994, allowed to accelerate lead (Pb
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
) ions
to 158 A GeV. At the BNL, a gold (Au
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
)-ion beam with energy up to
11 A GeV became available at that time. The smaller beam energy per nucleon of the heavier Pb ions compared
with that for sulfur
reflects their smaller ratio of particle charge to
particle mass, given a fixed magnetic field strength
used to bend the beam into a circular orbit in an accelerator.
At the BNL, the Relativistic Heavy Ion Collider (RHIC), was completed
in 1999 and it allowed the study of colliding nuclear beams at up
to 100 A GeV. This new energy domain achieved with colliding beams
has extended the reach of experiments considerably. in 2008 the Large Hadron
Collider (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...
) set in the 27-km CERN-LEP tunnel was inaugurated. It comprises an
important heavy-ion program at energies about a factor of 30 greater
than those of the RHIC. heavy Ion data from the LHC will become available in 2010.