An even stronger signature of strangeness enhancement is the highly enhanced production of strange antibaryons. This means that the abundance of strange quarks is sensitive to the conditions, structure and dynamics of the deconfined matter phase, and if their number is large it can be assumed that deconfinement conditions were reached. Conveniently, the mass of strange quarks and antiquarks is equivalent to the temperature or energy at which protons, neutrons and other hadrons dissolve into quarks. Therefore, any strange quarks or antiquarks observed in experiments have been "freshly" made from the kinetic energy of colliding nuclei, with gluons being the catalyst. Unlike the up and down quarks, strange quarks are not brought into the reaction by the colliding nuclei. This was the first observable of quark–gluon plasma proposed in 1980 by Johann Rafelski and Rolf Hagedorn. The experimental and theoretical work relies on the idea of strangeness enhancement. The diagnosis and the study of the properties of quark–gluon plasma can be undertaken using quarks not present in matter seen around us. Recent work by the ALICE collaboration at CERN has opened a new path to study of QGP and strangeness production in very high energy pp collisions. Comprehensive experimental evidence about its properties is being assembled. Strangeness as a signature of QGP was first explored in 1983. New experimental facilities, FAIR at the GSI Helmholtz Centre for Heavy Ion Research (GSI) and NICA at JINR, are under construction. Preparatory work, allowing for these discoveries, was carried out at the Joint Institute for Nuclear Research (JINR) and Lawrence Berkeley National Laboratory (LBNL) at the Bevalac. In this way, it is possible to study conditions akin to those in the early Universe at the age of 10–40 microseconds.ĭiscovery of this new QGP state of matter has been announced both at CERN and at Brookhaven National Laboratory (BNL). This is so since practically all QGP components flow out at relativistic speed. After this brief time the hot drop of quark plasma evaporates in a process called hadronization. Scientists achieve this using particle collisions at extremely high speeds, where the energy released in the collision can raise the subatomic particles' energies to an exceedingly high level, sufficient for them to briefly form a tiny amount of quark–gluon plasma that can be studied in laboratory experiments for little more than the time light needs to cross the QGP fireball, thus about 10 −22 s. In order to recreate this deconfined phase of matter in the laboratory it is necessary to exceed a minimum temperature, or its equivalent, a minimum energy density. This is possible because at a high temperature the early universe is in a different vacuum state, in which normal matter cannot exist but quarks and gluons can they are deconfined (able to exist independently as separate unbound particles). This gas is called quark–gluon plasma (QGP), since the quark-interaction charge ( color charge) is mobile and quarks and gluons move around. The collisions happened at such extreme velocities that the nuclei are "pancaked" because of Lorentz contraction.įree quarks probably existed in the extreme conditions of the very early universe until about 30 microseconds after the Big Bang, in a very hot gas of free quarks, antiquarks and gluons. Similar considerations are at present made for the heavier charm flavor, which is made at the beginning of the collision process in the first interactions and is only abundant in the high-energy environments of CERN's Large Hadron Collider.Ĭollision between two highly-energetic nuclei create an extremely dense environment, in which quarks and gluons may interact as free particles for brief moments. When quark–gluon plasma disassembles into hadrons in a breakup process, the high availability of strange antiquarks helps to produce antimatter containing multiple strange quarks, which is otherwise rarely made. The dominant mechanism of production involves gluons only present when matter has become a quark–gluon plasma. The abundance of strange quarks is formed in pair-production processes in collisions between constituents of the plasma, creating the chemical abundance equilibrium. The word plasma signals that color charged particles (quarks and/or gluons) are able to move in the volume occupied by the plasma. QGP (also known as quark matter) is an interacting localized assembly of quarks and gluons at thermal (kinetic) and not necessarily chemical (abundance) equilibrium. Unlike up and down quarks, from which everyday matter is made, heavier quark flavors such as strangeness and charm typically approach chemical equilibrium in a dynamic evolution process. Strangeness production in relativistic heavy ion collisions is a signature and a diagnostic tool of quark–gluon plasma (QGP) formation and properties.
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