Event by Event Net Charge Fluctuations

We present analyses of event-by-event dynamical net charge fluctuations measured in 130 and 200 GeV Au Au collisions with the STAR detector. The dynamical net charge fluctuations are evaluated using the $\nu_{+-,dyn}$ observable. Dynamical fluctuations measured in Au Au collisions at 130 and 200 GeV are finite, and exceed charge conservation limits. They deviate from a perfect 1/N scaling and provide an indication that the collision dynamics varies with collision centrality.Comment: 6 pages, 3 figures, Proc of 19th Nuclear Dynamics Conf at Breckenridge, Colorado, Feb 8-15, 200

Search for Conical Emission with Three-Particle Correlations

We present preliminary STAR results on 3-particle azimuthal angle correlation studies in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The studies are carried out at mid-rapidity between a trigger particle with 3 $\le p_{\perp} \le$ 4 GeV/c and two associated particles in 1 $\le p_{\perp} \le$ 2 GeV/c. A cumulant analysis reveals finite 3-particle azimuthal correlations, dominated by near and away side particle correlations consistent with jet production, and jet-flow correlations. We use a two-component model to remove underlying background correlations. This analysis indicates the presence of the conical emission signals in central Au+Au collisions within the model assumptions about background composition and normalization.Comment: Proceedings for STAR talk presented at Quark Matter 2006, 4 pages 2 figures, Version 2: typos corrected, references adde

Methods for the Study of Transverse Momentum Differential Correlations

We introduce and compare three differential correlation functions for the study of transverse momentum correlation in $p+p$ and $A+A$ collisions. These consist of {\it inclusive}, {\it event-wise} and a differential version of the correlation measure $\tilde C$ introduced by Gavin \cite{Gavin} for experimental study of the viscosity per unit entropy of the matter produced in $A+A$ collisions. We study the quantitative difference between the three observables on the basis of PYTHIA simulations of $p+p$ collisions and $A+A$ collisions consisting of an arbitrary superposition of $p+p$ collision events at $\sqrt{s} =$200 GeV. We observe that {\it inclusive} and {\it event-wise} correlation functions are remarkably identical to each other where as the observable $\tilde C$ differs from the two. We study the robustness and efficiency dependencies of these observables based on truncated Taylor expansions in efficiency in $p+p$ collisions and on the basis of Monte Carlo simulation using an adhoc detector efficiency parameterization. We find that all the three observables are essentially independent of detector efficiency. We additionally study the scaling of the correlation measures and find all the observables exhibit an approximate $1/N$ dependence of the number of participants ({\it N}) in $A+A$ collisions. Finally, we study the impact of flow-like anisotropy on the {\it inclusive} correlation function and find flow imparts azimuthal modulations similar to those observed with two-particle densities.Comment: 19 pages, 8 figure

Three-particle cumulant Study of Conical Emission

We discuss the sensitivity of the three-particle azimuthal cumulant method for a search and study of conical emission in central relativistic $A+A$ collisions. Our study is based on a multi-component Monte Carlo model which include flow background, Gaussian mono-jets, jet-flow, and Gaussian conical signals. We find the observation of conical emission is hindered by the presence of flow harmonics of fourth order ($v_4$) but remains feasible even in the presence of a substantial background. We consider the use of probability cumulants for the suppression of 2$^{nd}$ order flow harmonics. We find that while probability cumulant significantly reduce $v_2^2$ contributions, they also complicate the cumulant of jets, and conical emission. The use of probability cumulants is therefore not particularly advantageous in searches for conical emission. We find the sensitivity of the (density) cumulant method depends inextricably on strengths of $v_2$, $v_4$, background and non-Poisson character of particle production. It thus cannot be expressed in a simple form, and without specific assumptions about the values of these parameters.Comment: 12 figures, accepted for publication in PR

Transverse Radial Flow Effects on Two- and Three-Particle Angular Correlations

We use a simple a transverse radial boost scenario coupled to PYTHIA events to illustrate the impact radial flow may have on two- and three-particle correlation functions measured in heavy-ion collisions. We show that modest radial velocities can impart strong modifications to the correlation functions, some of which may be interpreted as same side ridge and away side structure that can mimic conical emission.Comment: 7 figures, 9 pages, Material presented in part by Pruneau at HOC 07, Montreal, Canada Accepted for publication in Nucl Phys A (Jan 2008

Covariance of Antiproton Yield and Source Size in Nuclear Collisions

We confront for the first time the widely-held belief that combined event-by-event information from quark gluon plasma signals can reduce the ambiguity of the individual signals. We illustrate specifically how the measured antiproton yield combined with the information from pion-pion HBT correlations can be used to identify novel event classes.Comment: 8 pages, 5 figures, improved title, references and readability; results unchange

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe