DOE OSTI2013
At the most fundamental level, ordinary matter is composed of quarks and gluons bound together to form hadrons. The protons and neutrons that form atomic nuclei are members of this class. At most temperatures quarks are very tightly bound together by gluons, the particles which carry the strong force, however, at extremely high temperatures equal to approximately 100,000 times that at the sun’s core, the quarks possess the energy to separate and transition to a state of matter consisting of individual quarks and gluons. In this state the quarks and gluons are asymptotically free. This state is known as the Quark Gluon Plasma (QGP) is believed to be the state of matter a few microseconds after the Big Bang. \ Over the last thirty years several laboratories have been focused on creating the (QGP) in a controlled environment so that its properties can be more easily investigated. Programs at the “Relativistic Heavy Ion Collider (RHIC)” at Brookhaven National Laboratory (BNL) and more recently the Large Hadron Collider (LHC)’s “A Large Ion Collider Experiment (ALICE)” at the European Center for Nuclear Research (CERN) have been dedicated to exploring the physics of the QGP. In heavy ion collisions, experiment has shown that an indicator of the existence of the QGP is the enhancement of strange hadrons emanating from the collision. In understanding the enhancement of strange particles emitted from collisions it is noted that no strange quarks existed in the colliding nuclei prior to the collision, from which it follows that strange quarks are created during the collision. Since strangeness is a conserved quantity, strange quarks are created as quark-antiquark pairs ($s\overline{s}$) by strong or electro-weak interactions. Additionally, since the mass of the ($s\overline{s}$) pair is comparable to the critical temperature for QGP formation it can be expected that strange particle enhancement will occur. Using perturbative QCD it has been shown that two primary mechanisms exist for strange quark creation. They are annihilation of light quarks, $q\overline{q}$ →$s\overline{s}$, and gluon fusion, gg →$s\overline{s}$. The time associated with light quark annihilation was found to be too long when compared to the time needed to reach QGP equilibrium, thereby making the gluon fusion mechanism the dominant process for strange quark creation. Figure 1 illustrates strange quark creation by gluon fusion in QGP and the formation of strange hadrons.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗