The Elliptic Flow Study In Proton-proton Collisions At Ultra-high Energy

Quantum Chromodynamics predicted that, when the temperature of the matter is extremely high, or when the baryon number density is extremely large, there will be a phase transition from the confined phase to the deconfined phase, thus quarks and gluons are then deconfined to form a Quark-Gluon-Plasma (QGP). This could be accomplished in the high energy heavy ion collision experiments, where lots of energy deposited by the colliding nuclear matter cumulated in a very limited space.Currently, experiments at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RⅢC), have tentatively reported that a quark-gluon plasma in the Au+Au collisions at (?)= 200GeV has been created. However, this QGP has small viscosity, just like the state of strongly coupled plasma (sQGP). There are several signals which could be used to indicate the formation of QGP matter, the elliptic flow is described as one of the most important signals, it has already been detected in heavy ion collision experiments.Yet, till now, no such signals have been detected in the proton-proton collision experiments. In November of 2010, the experiment of proton-proton collisions at (?)= 7TeV in the Large Hadron Collider (LHC) reported that, at the final state, multiplicities have reached to dN/dη≥30. This may suggest that, in higher en-ergy proton-proton collision experiment, the charged particle multiplicities may be higher, thus the elliptic flow may be detected. Some theoretical work indicate that the elliptic flow would be detected in the future experiment of proton-proton collisions at (?)=14TeV in LHC.The PACIAE model, which includes the process of parton rescattering before hadronization and the hadron rescattering after hadronization, is employed to study the relationship between elliptic flow and eccentricity, we find that the larger eccen-tricity could result in the larger elliptic flow, which reflects the anisotropy in trans-verse moumentum space. Also, the elliptic flow would increase with the increasing of colliding energy or transverse momentum, untill it reaches the maximum value, 2.5%, and then turns to saturation. This is similar to the other predictions.Meanwhile, by analyzing the relationship between the elliptic flow and the mul-tiplicity of charged particles, we predicted the relationship between the elliptic flow and the impact parameter, the results show that, the elliptic flow increases, as the in-crease of the multiplicities of the charged particles, that is, the more central collision would produce the greater value of elliptic flow. For comparision, the elliptic flow is also studied by using the PYTHIA model, we find that the elliptic flow is very small, just independent of the charged particle multiplicities. We deem that, this could be attributed to the effects of the parton and hadron rescattering mechanism in PACIAE model, since the parton and hadron rescattering may play an important role in the high energy heavy ion collisions.