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

Simulation studies of R2(Δη,Δφ)\rm{R_{2}}(\Delta\eta, \Delta\varphi) and P2(Δη,Δφ)\rm{P_{2}}(\Delta\eta, \Delta\varphi) correlation functions in pp collisions with the PYTHIA and HERWIG models

We report studies of charge-independent (CI) and charge-dependent (CD) two-particle differential-number correlation functions, $\rm{R_{2}}(\Delta\eta, \Delta\varphi)$, and transverse momentum ($p_{\rm T}$) correlation functions, $\rm{P_{2}}(\Delta\eta, \Delta\varphi)$, of charged particles in $\sqrt{\textit{s}}$ = 2.76 TeV pp collisions with the PYTHIA and HERWIG models. Model predictions are presented for inclusive charged hadrons ($h^\pm$), as well as pions ($\pi^\pm$), kaons (K$^\pm$), and (anti-)protons ($\rm \bar{p}$/p) in the ranges $0.2 < \textit{p}_{\rm T} \le 2.0~\rm{GeV}/\textit{c}$, $2.0 < \textit{p}_{\rm T} \le 5.0~\rm{GeV}/\textit{c}$, and $5.0 < \textit{p}_{\rm T} \le 30.0~\rm{GeV}/\textit{c}$, with full azimuthal coverage in the range $|\eta|< 1.0$. We compare the model predictions for the strength and shape of the $\rm{R_{2}}$ and $\rm{P_{2}}$ correlators as these pertain to recent measurements by the ALICE collaboration. The $\rm{R_{2}}$ and $\rm{P_{2}}$ correlation functions estimated with PYTHIA and HERWIG exhibit qualitatively similar near-side and away-side correlation structures but feature important differences. Our analysis indicates that comparative studies of $\rm{R_{2}}$ and $\rm{P_{2}}$ correlation functions would provide valuable insight towards the understanding of particle production in pp collisions, and by extension, should also be useful in studies of heavy-ion collisions. Comparison of the $\Delta \eta$ dependence of $\rm{R_{2}}$ and $\rm{P_{2}}$ could contribute, in particular, to a better understanding and modeling of the angular ordering of particles produced by hadronization in jets, as well as a better description of jet fragmentation functions of identified species at low momentum fraction $(z)$.Comment: 22 pages, 24 captioned 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