A. M. Poskanzer

Methods for analyzing anisotropic flow in relativistic nuclear collisions

The strategy and techniques for analyzing anisotropic flow (directed, elliptic, etc.) in relativistic nuclear collisions are presented. The emphasis is on the use of the Fourier expansion of azimuthal distributions. We present formulae relevant for this approach, and in particular, show how the event multiplicity enters into the event plane resolution. We also discuss the role of non-flow correlations and a method for introducing flow into a simulation.

Collective phenomena in non-central nuclear collisions

Recent developments in the field of anisotropic flow in nuclear collision are reviewed. The results from the top AGS energy to the top RHIC energy are discussed with emphasis on techniques, interpretation, and uncertainties in the measurements.

Plastic Ball experiments

The Plastic Ball spectrometer is a 4 pi detector with particle identification for charged particles. It was first used at the Berkeley Bevalac to study nucleus-nucleus collisions at beam energies of hundreds of MeV per nucleon. Recently it has been moved to the CERN SPS for studies of target fragmentation at energies of hundreds of GeV per nucleon. The authors present a complete review of the spectrometer and the physics obtained at the Bevalac, with some recent additions from the work at CERN.

FastBit: interactively searching massive data

As scientific instruments and computer simulations produce more and more data, the task of locating the essential information to gain insight becomes increasingly difficult. FastBit is an efficient software tool to address this challenge. In this article, we present a summary of the key underlying technologies, namely bitmap compression, encoding, and binning. Together these techniques enable FastBit to answer structured (SQL) queries orders of magnitude faster than popular database systems. To illustrate how FastBit is used in applications, we present three examples involving a high-energy physics experiment, a combustion simulation, and an accelerator simulation. In each case, FastBit significantly reduces the response time and enables interactive exploration on terabytes of data.

Forward and transverse energy distributions in oxygen-induced reactions at 60 A GeV and 200 A GeV

Abstract Results are presented from reactions of 60 A GeV and 200 A GeV 16O projectiles with C, Cu, Ag, and Au nuclei. Energy spectra measured at zero degrees and transverse energy distributions in the pseudorapidity range from 2.4 to 5.5 are shown. The average transverse energy per participant is found to be nearly independent of target mass. Estimates of nuclear stopping and of attained energy densities are made.

The physics of the centrality dependence of elliptic flow

Abstract The centrality dependence of elliptic flow and how it is related to the physics of expansion of the system created in high energy nuclear collisions is discussed. Since in the hydro limit the centrality dependence of elliptic flow is mostly defined by the elliptic anisotropy of the overlapping region of the colliding nuclei, and in the low density limit by the product of the elliptic anisotropy and the multiplicity, we argue that the centrality dependence of elliptic flow should be a good indicator of the degree of equilibration reached in the reaction. Then we analyze experimental data obtained at AGS and SPS energies. The observed difference in the centrality dependence of elliptic flow could imply a transition from a hadronic to a partonic nature of the system evolution. Finally we exploit the multiplicity dependence of elliptic flow to make qualitative predictions for RHIC and LHC.

Elliptic flow in the Gaussian model of eccentricity fluctuations

Abstract We discuss a specific model of elliptic flow fluctuations due to Gaussian fluctuations in the initial spatial x and y eccentricity components { 〈 ( σ y 2 − σ x 2 ) / ( σ x 2 + σ y 2 ) 〉 , 〈 2 σ x y / ( σ x 2 + σ y 2 ) 〉 } . We find that in this model v 2 { 4 } , elliptic flow determined from 4-particle cumulants, exactly equals the average flow value in the reaction plane coordinate system, 〈 v RP 〉 , the relation which, in an approximate form, was found earlier by Bhalerao and Ollitrault in a more general analysis, but under the same assumption that v 2 is proportional to the initial system eccentricity. We further show that in the Gaussian model all higher order cumulants are equal to v 2 { 4 } . Analysis of the distribution in the magnitude of the flow vector, the Q-distribution, reveals that it is totally defined by two parameters, v 2 { 2 } , the flow from 2-particle cumulants, and v 2 { 4 } , thus providing equivalent information compared to the method of cumulants. The flow obtained from the Q-distribution is again v 2 { 4 } = 〈 v RP 〉 .

Charged-particle distributions in 16O induced nuclear reactions at 60 and 200 A GeV

Abstract Results from 16 O induced nuclear interactions with C, Cu, Ag and Au targets at 60 and 200 A GeV are presented. Multiplicity and pseudorapidity-density distributions of charged particles and their dependence on the target mass number are reported. The increase in the particle density with increasing centrality, characterized by the energy flux at zero degrees, is investigated. Comparisons with the Fritiof model reveal systematic differences.

The mid-rapidity calorimeter for the relativistic heavy-ion experiment WA80 at CERN

Abstract A sampling calorimeter designed for use at mid-rapidity in the relativistic heavy-ion experiment WA80 at CERN is described. Calibration and performance results are presented. Over the energy range of 2 to 50 GeV, the response of the mid-rapidity calorimeter was linear, and its energy resolution σ E was found to be given by 0.014 + 0.11 √E and 0.034+0.34 √E for electromagnetic and hadronic showers, respectively. Signal ratios of 1.2 and 1.4 were obtained for the e h ratio of the lead-scintillator electromagnetic section and the iron-scintillator hadronic section, respectively. The calorimeter provided an accurate transverse energy trigger. The response and resolution for high-energy heavy ions were slightly better than anticipated on the basis of the low-energy calibrations.

Strange particle production in nuclear collisions at 200 GeV per nucleon

AbstractMultiplicities and spectra of strange particles (