Abstract
The early universe consists of bacis particles like quarks and gluons. Their interactions are controlled by strong interactions. In order to produce this new kind of matters, one can collide heavy ions. Large amount of energy will be transformed into particles. These particles form a matter with extremely high temperature. Usually this kind of matter can only be produced in heavy ion collisions, not nucleon collisions. But the recent experimental data indicate that it may also generate this kind of matter. The signal in nucleon collisions are taken as a baseline for heavy ion collisions, and other theoretical and experimental studies are based on this assumption that no hot medium is produced in nucleon collisions. If this new matter is also produced in nucleon collisions, this will affect the signals in heavy ion collisions. This work studies the momentum correlations of heavy quark pairs in the small colliding system such as proton-proton collisions based on the Langevin equation. With the production of deconfined hot medium, heavy quarks moving in the opposite direction can suffer energy loss and random kicks from the thermal medium. Moving in different directions, heavy quark and its anti-quark will suffer different random kicks from the thermal medium, which will change their momentum randomly. Their momentum correlations will be modified after moving out of the hot medium. Finally when heavy quark and anti-quark move out of the hot medium, their momentum is not in the opposite direction. Insteand, they move with a angular less than pi. We propose the momentum correlation of D mesons as a probe of the early stage of the proton-proton collisions, where the deconfined medium may be produced.
Highlights
The concept of quark was first proposed by M
For the line of pT = 1 GeV c, the value of p(t) p0 in the later stage even becomes lager than unit, which means charm quarks with pT = 1 GeV c can reach kinetic thermalization at around 0.2 < t < 0.4 fm c, and they will pick up more energy from the bulk medium due to the random kicks in the Langevin equation
With the production of deconfined hot medium, heavy quarks moving in the opposite direction can suffer energy loss and their momentum correlations will be modified after moving out of the hot medium
Summary
The concept of quark was first proposed by M. Because the non-Abelian nature of QCD theory, quarks and gluons are confined (color confinement) within the hadrons at low energy scale, while asymptotic at high energy scale. For this reason, a new state of matter has been proposed, Quark Gluon Plasma (QGP). One amazing results in pp collisions is the long-range ridge structure in two particle azimuthal correlations with a large pseudo-rapidity in high multiplicities [20, 21] Such phenomenons have been discovered in AA collisions and interpreted as a signature of QGP collective motion.
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