Azimuthal Anisotropy And Longitudinal Property Of Charge Balance Function In Relativistic Heavy Ion Collisions

A Quark-Gluon Plasma(QGP) is a phase of quantum chromodynamics (QCD) which consists of (almost) free quarks and gluons. It only exists at extremely high temperature and/or density, and is believed to indwell in the first few microseconds after the Big Bang. The goal of the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is to create the condition which may lead to the formation of the QGP and study the property of the new kind of matter.Collective flow and jet quenching are two main results to claim the discovery of QGP at RHIC. They described the collective motions of soft partons and the energy loss of hard partons traversing trough the medium, respectively. The productions of soft and hard paxtons dominate in different period of a collision, and result in the different behaviors of the observations. In this thesis, we study the azimuthal anisotropy in different pT range, which can offer the connection and transition between the soft and hard processes. Thus it may help us to map the time line of the heavy ion collisions and give the insight information of the dynamics.Usually, the azimuthal anisotropy is described by Fourier coefficients of the particle momentum distribution. It comes from the collective expansion of the bulk matter, arising from the density gradient of the overlap region of two colliding nuclei in non-central collision. At low pT, the 2nd harmonic called elliptic flow, v2, comes close to values predicted by hydrodynamics, which indicates that the medium behaves like ideal liquid. While at intermediate pT, the so called number of constituent quark (NCQ) scaling is found, and it implies that hadrons are produced out of a deconfined partonic state by coalescence or recombination. However, the models that take the realistic effects into account, e.g., adding sea quarks and gluons to the hadron structure and considering the momentum distribution of quarks inside hadrons, may lead to the violation of NCQ scaling. At high pT, when hard partons, resulting from initial hard scatterings, transverse the asymmetrical overlap region, they experience different path lengths and therefore different energy loss which leads to an azimuthal anisotropy.In this thesis, we measure elliptic flow of identified particles (π, p (p), KSO,∧(∧)) up to 6 GeV/c in Au+Au collisions (?)=200 GeV. A deviation from the exact NCQ of pions compared to baryons by approximately 20% from 0.5 up to pT/nq(?)1.5 GeV/c, while models with realistic effects included can only explain a deviation up to 5% from a meson-baryon difference.It is so far the first observation of breaking of NCQ scaling in experiment. Since the Coalescence models require a significant fragmentation contribution to account for the large deviation from scaling at the upper end of the measured pT/nq and (mT-m)/nq range. This suggests that fragmentation may kick in and becomes more dominant in this region. We also measure v2 for charged particles up to 15 GeV/c. The sizable v2 has been observed up to pT=10 GeV/c. This is consistent with the scenario of parton energy loss, which is also the evidence for the formation of very dense matter.The ratio v4/v22 is proposed as a probe of ideal hydrodynamic behavior, and it is directly related to the degree of thermalization. The measured ratio v4/v22 is studied for both charged particle and identified particles. We find that the ratio v4/v22 is about 1 when pT is about 2 GeV/c for all the particles, which is larger than the ideal hydrody-namic prediction. This may be due to the fluctuation of the measured v2 and v4, but also may indicate the incomplete thermalization of the system.The charge balance function (BF) is an observable specifically designed to measure the charge balance. It is sensitive to the mechanisms of charge formation and the subsequent relative diffusion of the balancing charges. Therefore, it can provide insight into the particle production processes in elementary collisions.In this thesis, it is the first time to observed the boost invariance of BF in both hadron-hadron and nuclear-nuclear collisions. Inπ+p and K+p collisions from NA22/EHS at (?)=22 GeV, the BF is found to be invariant under longitudinal boost over the whole rapidity (y) range of produced particles (-5 (<Δη>)), can be considered as a probe of late hadronization. Inπ+p and K+p collisions from NA22/EHS at (?)= 22 GeV, where no QGP phase space is expected, (Δy) is found to be narrower as multi-plicity increasing. To investigate this trivial effect, we studied (Δy) in p+p collisions at (?)= 22,64,130,200 GeV using PYTHIA Monte-Carlo generator. The result shows that the width of BF first decreases with increasing multiplicity, and it changes little when multiplicity is about larger than 20. When the same size of observation window is used, the width of BF is independent of colliding energy, which is consistent with expec-tation of instantaneous hadronization in hadron-hadron collisions. Also, (Δy) is found sensitive to the size of observed windows, and it is consistent with charge correlation and fluctuation. In Au+Au collisions from STAR/RHIC at (?)=200 GeV, <Δη> decreases with increasing transverse momentum and increasing centrality. The origin of these narrowings is associated with transverse radial flow and their possible connections should provide more insight into the particle production dynamics in relativistic heavy ion collisions.