High energy nuclear physics

Last updated April 07, 2019

High-energy nuclear physics studies the behaviour of nuclear matter in energy regimes typical of high energy physics. The primary focus of this field is the study of heavy-ion collisions, as compared to lower atomic mass atoms in other particle accelerators. At sufficient collision energies, these types of collisions are theorized to produce the quark–gluon plasma. In peripheral nuclear collisions at high energies one expects to obtain information on the electromagnetic production of leptons and mesons which are not accessible in electron-positron colliders due to their much smaller luminosities.^[1]^[2]^[3]

A quark–gluon plasma (QGP) or quark soup is a state of matter in quantum chromodynamics (QCD) which exists at extremely high temperature and/or density. This state is thought to consist of asymptotically free strong-interacting quarks and gluons, which are ordinarily confined by color confinement inside atomic nuclei or other hadrons. This is in analogy with the conventional plasma where nuclei and electrons, confined inside atoms by electrostatic forces at ambient conditions, can move freely. Artificial quark matter, which has been produced at Brookhaven National Laboratory's Relativistic Heavy Ion Collider and CERN's Large Hadron Collider, can only be produced in minute quantities and is unstable and impossible to contain, and will radioactively decay within a fraction of a second into stable particles through hadronization; the produced hadrons or their decay products and gamma rays can then be detected. In the quark matter phase diagram, QGP is placed in the high-temperature, high-density regime, whereas ordinary matter is a cold and rarefied mixture of nuclei and vacuum, and the hypothetical quark stars would consist of relatively cold, but dense quark matter. It is believed that up to a few milliseconds after the Big Bang, known as the quark epoch, the Universe was in a quark–gluon plasma state.

Previous high-energy nuclear accelerator experiments have studied heavy-ion collisions using projectile energies of 1 GeV/nucleon up to 158 GeV/nucleon. Experiments of this type, called "fixed target" experiments, primarily accelerate a "bunch" of ions (typically around $10^{6}$ to $10^{8}$ ions per bunch) to speeds approaching the speed of light (0.999c) and smash them into a target of similar heavy ions. While all collision systems are interesting, great focus was applied in the late 1990s to symmetric collision systems of gold beams on gold targets at Brookhaven National Laboratory's Alternating Gradient Synchrotron (AGS) and uranium beams on uranium targets at CERN's Super Proton Synchrotron.

Particle accelerator device to propel charged particles to high speeds

A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.

The speed of light in vacuum, commonly denoted $c$ , is a universal physical constant important in many areas of physics. Its exact value is 299,792,458 metres per second. It is exact because by international agreement a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1/299792458 second. According to special relativity, $c$ is the maximum speed at which all conventional matter and hence all known forms of information in the universe can travel. Though this speed is most commonly associated with light, it is in fact the speed at which all massless particles and changes of the associated fields travel in vacuum. Such particles and waves travel at $c$ regardless of the motion of the source or the inertial reference frame of the observer. In the special and general theories of relativity, $c$ interrelates space and time, and also appears in the famous equation of mass–energy equivalence $E = mc 2$ .

Gold Chemical element with atomic number 79

Gold is a chemical element with symbol Au and atomic number 79, making it one of the higher atomic number elements that occur naturally. In its purest form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the native element silver and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium.

Currently, high-energy nuclear physics experiments are being conducted at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) and in CERN's new Large Hadron Collider. The four primary experiments at RHIC (PHENIX, STAR, PHOBOS, and BRAHMS) study collisions of highly relativistic nuclei. Unlike fixed target experiments, collider experiments steer two accelerated beams of ions toward each other at (in the case of RHIC) six interaction regions. At RHIC, ions can be accelerated (depending on the ion size) from 100 GeV/nucleon to 250GeV/nucleon. Since each colliding ion possesses this energy moving in opposite directions, the maximum energy of the collisions can achieve a center of mass collision energy of 200GeV/nucleon for gold and 500GeV/nucleon for protons.

Brookhaven National Laboratory United States Department of Energy national laboratory

Brookhaven National Laboratory (BNL) is a United States Department of Energy 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. Its name stems from its location within the Town of Brookhaven, approximately 60 miles east of New York City.

The Relativistic Heavy Ion Collider is the first and one of only two operating heavy-ion colliders, and the only spin-polarized proton collider ever built. Located at Brookhaven National Laboratory (BNL) in Upton, New York, and used by an international team of researchers, it is the only operating particle collider in the US. 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. By colliding spin-polarized protons, the spin structure of the proton is explored.

The European Organization for Nuclear Research, known as CERN, is a European research organization that operates the largest particle physics laboratory in the world. Established in 1954, the organization is based in a northwest suburb of Geneva on the Franco–Swiss border and has 23 member states. Israel is the only non-European country granted full membership. CERN is an official United Nations Observer.

The ALICE (A Large Ion Collider Experiment) detector at the LHC at CERN is specialized in studying Pb-Pb nuclei collisions at a centre of mass energy of 2.76 TeV per nucleon pair. Other LHC detectors like CMS, ATLAS, and LHCb also have heavy ion programs.

History

The exploration of hot hadron matter and of multiparticle production has a long history initiated by theoretical work on multiparticle production by Enrico Fermi in the USA, and Lev Landau in the USSR. These efforts paved the way to the development in the early sixties of the statistical bootstrap model description of hadron production by Rolf Hagedorn.

Enrico Fermi was an Italian and naturalized-American physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1. He has been called the "architect of the nuclear age" and the "architect of the atomic bomb". He was one of very few physicists to excel in both theoretical physics and experimental physics. Fermi held several patents related to the use of nuclear power, and was awarded the 1938 Nobel Prize in Physics for his work on induced radioactivity by neutron bombardment and for the discovery of transuranium elements. He made significant contributions to the development of statistical mechanics, quantum theory, and nuclear and particle physics.

Lev Davidovich Landau was a Soviet physicist who made fundamental contributions to many areas of theoretical physics.

In particle physics, a hadron is a composite particle made of two or more quarks held together by the strong force in a similar way as molecules are held together by the electromagnetic force. Most of the mass of ordinary matter comes from two hadrons, the proton and the neutron.

First collisions

The first heavy ion collisions at modestly relativistic conditions were undertaken 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. The energy scale at the level of 1-2 GeV per nucleon attained initially yields compressed nuclear matter at few times normal nuclear density. The demonstration of the possibility of studying the properties of compressed and excited nuclear matter motivated research programs at much higher energies in accelerators available at BNL and CERN with relativist beams targeting laboratory fixed targets. The first collider experiments started in 1999 at RHIC and LHC begun colliding heavy ions at one order of magnitude higher energy in 2010.

Lawrence Berkeley National Laboratory (LBNL), commonly referred to as Berkeley Lab, is a United States national laboratory that conducts scientific research on behalf of the United States Department of Energy (DOE). It is located in the Berkeley Hills near Berkeley, California, overlooking the main campus of the University of California, Berkeley. It is managed and operated by the University of California.

The University of California, Berkeley is a public research university in Berkeley, California. It was founded in 1868 and serves as the flagship institution of the ten research universities affiliated with the University of California system. Berkeley has since grown to instruct over 40,000 students in approximately 350 undergraduate and graduate degree programs covering numerous disciplines.

The Bevatron was a particle accelerator — specifically, a weak-focusing proton synchrotron — at Lawrence Berkeley National Laboratory, U.S., which began operating in 1954. The antiproton was discovered there in 1955, resulting in the 1959 Nobel Prize in physics for Emilio Segrè and Owen Chamberlain. It accelerated protons into a fixed target, and was named for its ability to impart energies of billions of eV.

CERN operation

The LHC collider at CERN operates one month a year in the nuclear collision mode, with Pb-nuclei colliding at 2.76 TeV per nucleon pair, about 1500 times the energy equivalent of the rest mass. Overall 1250 valance quarks collide generating a hot quark-gluon soup. Heavy atomic nuclei stripped of their electron cloud are called heavy-ions, and one speaks of (ultra)relativistic heavy-ions when the kinetic energy exceeds significantly the rest mass energy, as it is the case at LHC. The outcome of such collisions is production of very many strongly interacting particles.

In August 2012 ALICE scientists announced that their experiments produced quark–gluon plasma with temperature at around 5.5 trillion degrees, the highest temperature mass achieved in any physical experiments thus far.^[4] This temperature is about 38% higher than the previous record of about 4 trillion degrees, achieved in the 2010 experiments at the Brookhaven National Laboratory.^[4] The ALICE results were announced at the August 13 Quark Matter 2012 conference in Washington, D.C.. The quark–gluon plasma produced by these experiments approximates the conditions in the universe that existed microseconds after the Big Bang, before the matter coalesced into atoms.^[5]

Objectives

There are several scientific objectives of this international research program:

The formation and investigation of a new state of matter made of quarks and gluons, the quark gluon plasma QGP which prevailed in early Universe in first 30 micro seconds;
The study of color confinement and the transformation of color confining = quark confining vacuum state to the excited state physicists call perturbative vacuum, in which quarks and gluons can roam free which occurs at Hagedorn temperature;
The study the origins of hadron (proton, neutron etc.) matter mass believed to be related to the phenomenon of quark confinement and vacuum structure.

Experimental program

This experimental program follows on a decade of research at the RHIC collider at BNL and almost two decades of studies using fixed targets at SPS at CERN and AGS at BNL. This experimental program has already confirmed that the extreme conditions of matter necessary to reach QGP phase can be reached. A typical temperature range achieved in the QGP created

T=300{\mbox{MeV/k}}=3.3\times 10^{12}{\mbox{K}}

is more than 100 000 times greater than in the center of the Sun. This corresponds to an energy density

\epsilon =10{\mbox{GeV/fm}}^{3}=1.8\times 10^{16}{\mbox{g cm}}^{-3}

.

The corresponding relativistic matter pressure is

P\simeq {\frac {1}{3}}\epsilon =0.52\times 10^{31}\,{\mbox{bar}}.

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References

↑ "Rutgers University Nuclear Physics Home Page". www.physics.rutgers.edu. Retrieved 5 February 2019.
↑ "Publications - High Energy Nuclear Physics (HENP)". www.physics.purdue.edu. Retrieved 5 February 2019.
↑ http://www.er.doe.gov/np/
1 2 Eric Hand (13 Aug 2012). "Hot stuff: CERN physicists create record-breaking subatomic soup". Nature News Blog. Retrieved 5 Jan 2019.
↑ Will Ferguson (14 August 2012). "LHC primordial matter is hottest stuff ever made". New Scientist . Retrieved 15 August 2012.

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[1] "Rutgers University Nuclear Physics Home Page". www.physics.rutgers.edu. Retrieved 5 February 2019.

[2] "Publications - High Energy Nuclear Physics (HENP)". www.physics.purdue.edu. Retrieved 5 February 2019.

[3] ttp://www.er.doe.gov/np/

[NatureNews-4] 1 2 Eric Hand (13 Aug 2012). "Hot stuff: CERN physicists create record-breaking subatomic soup". Nature News Blog. Retrieved 5 Jan 2019.

[5] Will Ferguson (14 August 2012). "LHC primordial matter is hottest stuff ever made". New Scientist . Retrieved 15 August 2012.