A dense form of matter is formed in relativistic heavy ion collisions. The constituent degrees of freedom in this dense matter are currently unknown. Long-range, forward-backward multiplicity correlations (LRC) are expected to arise due to multiple p
artonic interactions. Model independent and dependent arguments suggest that such correlations are due to multiple partonic interactions. These correlations are predicted in the context of the Dual Parton Model (DPM). The DPM describes soft partonic processes and hadronization. This model indicates that the underlying mechanism creating these long-range multiplicity correlations in the bulk matter is due to multiple partonic interactions. In this thesis, long-range multiplicity correlations have been studied in heavy ion (Au+Au and Cu+Cu) and hadron-hadron ({it pp}) collisions. The behavior has been studied as a function of pseudorapidity gap ($Deltaeta$) about $eta$ = 0, the centrality, atomic number, and incident energy dependence of the colliding particles. Strong, long-range correlations ($Deltaeta >$ 1.0) as a function of $Deltaeta$ are found for central collisions of %(full overlap) heavy ions at an energy of $sqrt{s_{NN}}$ = 200 GeV. This indicates substantial amounts of dense partonic matter are formed in central heavy ion collisions at an energy of $sqrt{s_{NN}}$ = 200 GeV.
A study of the first four moments (mean, variance, skewness, and kurtosis) and their products ($kappasigma^{2}$ and $Ssigma$) of the net-charge and net-proton distributions in Au+Au collisions at $sqrt{rm s_{NN}}$ = 7.7-200 GeV from HIJING simulation
s has been carried out. The skewness and kurtosis and the collision volume independent products $kappasigma^{2}$ and $Ssigma$ have been proposed as sensitive probes for identifying the presence of a QCD critical point. A discrete probability distribution that effectively describes the separate positively and negatively charged particle (or proton and anti-proton) multiplicity distributions is the negative binomial (or binomial) distribution (NBD/BD). The NBD/BD has been used to characterize particle production in high-energy particle and nuclear physics. Their application to the higher moments of the net-charge and net-proton distributions is examined. Differences between $kappasigma^{2}$ and a statistical Poisson assumption of a factor of four (for net-charge) and 40% (for net-protons) can be accounted for by the NBD/BD. This is the first application of the properties of the NBD/BD to describe the behavior of the higher moments of net-charge and net-proton distributions in nucleus-nucleus collisions.
Dynamical fluctuations in global conserved quantities such as baryon number, strangeness, or charge may be enhanced near a QCD critical point. Charge dependent results from new measurements of dynamical $K/pi$, $p/pi$, and $K/p$ ratio fluctuations ar
e presented. The STAR experiment has performed a comprehensive study of the energy dependence of these dynamical fluctuations in Au+Au collisions at the energies $sqrt{s_{NN}}$ = 7.7-200 GeV using the observable, $ u_{rm dyn}$. These results are compared to previous measurements and to theoretical predictions. Various proposed scaling scenarios that attempt to remove the intrinsic volume dependence of $ u_{rm dyn}$ and to simplify comparisons between experimental measurements are also considered. Constructing an intensive quantity allows for a direct connection to thermodynamic predictions.
The measurement of particle correlations and fluctuations has been suggested as a method to search for the existence of a phase transition in relativistic heavy ion collisions. If quark-gluon matter is formed in the collision of relativistic heavy io
ns, measuring these correlations could lead to a determination of the presence of partonic degrees of freedom within the collision. Additionally, non-statistical fluctuations in global quantities such as baryon number, strangeness, or charge may be observed near a QCD critical point. Results for short and long-range multiplicity correlations (forward-backward) are presented for several systems (Au+Au and Cu+Cu) and energies (e.g. $sqrt{s_{NN}}$ = 200, 62.4, and 22.4 GeV). For the highest energy central A+A collisions, the correlation strength maintains a constant value across the measurement region. In peripheral collisions, at lower energies, and in pp data, the maximum appears at midrapidity. Comparison to models with short-range (HIJING) and both short and long-range interactions (Parton String Model) do not fully reproduce central Au+Au data. Preliminary results for K/$pi$ fluctuations are also shown as a function of centrality in Cu+Cu collisions at $sqrt{s_{NN}}$ = 22.4 GeV.
A discussion of results for short and long-range multiplicity correlations (forward-backward) are presented for several systems (Au+Au, Cu+Cu, and pp) and energies (e.g. $sqrt{s_{NN}}$ = 200, 62.4, and $approx$ 20 GeV). These correlations are measure
d with increasing values of a gap in pseudorapidity, from no gap at midrapidity to a separation of 1.6 units ($|eta|$ = 0.8). For the highest energy, central A+A collisions, the forward-backward correlation strength maintains a constant value across the measurement region. In peripheral collisions, at lower energies, and in pp data, the maximum appears at midrapidity. This result may indicate the possible formation of high density matter for central A+A collisions at $sqrt{s_{NN}}$ = 200 GeV.
