A. Petridis

Negative Particle Production in Nuclear Collisions at 60-GeV/Nucleon and 200-GeV/Nucleon

The results on spectra of negative particles produced in16O+Au andp-Au collisions at 200 GeV/nucleon and16O+Au at 60 GeV/nucleon are presented. The correlations of average rapidity and average transverse momentum with event multiplicity are studied. Spectral shapes are similar for central16O+Au andp-Au collisions. The transverse momentum and rapidity distributions for central16O+Au andp-Au collisions differ strongly from corresponding distributions forp+p interactions. The FRITIOF model fails to describe the shapes of the transverse momentum distributions. The simple thermodynamical model of a single fireball does not fit the midrapidity transverse momentum distributions, and the rapidity distributions.

Transition Radiation Spectra of Electrons from 1 to 10 GeV/c in Regular and Irregular Radiators

Abstract We present measurements of the spectral distribution of transition radiation generated by electrons of momentum 1–10xa0GeV/c in different radiator types. We investigate periodic foil radiators and irregular foam and fiber materials. The transition radiation photons are detected by prototypes of the drift chambers to be used in the Transition Radiation Detector (TRD) of the ALICE experiment at CERN, which are filled with a Xe, CO2 (15%) mixture. The measurements are compared to simulations in order to enhance the quantitative understanding of transition radiation production, in particular the momentum dependence of the transition radiation yield.

Development of a RICH detector for ultrarelativistic heavy ion collisions

Abstract A single module of an intended RICH detector for ultrarelativistic heavy ion collisions (NA35 experiment at CERN) has been tested with 1.5–3 GeV/ c positive hadrons. The Cherenkov photons from a liquid freon (C 6 F 14 ) radiator have been focused by a spherical mirror into a multistep avalanche chamber equipped with an optical readout. The analysis of the events and the results of the reconstruction of the Cherenkov angle are presented. A good agreement between experiment and simulation was observed.

Multiplicity distributions in small phase-space domains in central nucleus-nucleus collisions

Multiplicity distributions of negatively charged particles have been studied in restricted phase space intervals for central S+S, O+Au and S+Au collisions at 200 GeV/nucleon. It is shown that multiplicity distributions are well described by a negative binomial form irrespectively of the size and dimensionality of phase space domain. A clan structure analysis reveals interesting similarities between complex nuclear collisions and a simple partonic shower. The lognormal distribution agrees reasonably well with the multiplicity data in large domains, but fails in the case of small intervals. No universal scaling function was found to describe the shape of multiplicity distributions in phase space intervals of varying size.

A new Coulomb correction method for Bose-Einstein correlations, based on the pi+pi- correlation measurements

We present the measured correlation functions for π+π−, π−π− and π+π+ pairs in central S+Ag collisions at 200 GeV per nucleon. The Gamov function, which has been traditionally used to correct the correlation functions of charged pions for the Coulomb interaction, is found to be inconsistent with all measured correlation functions. Certain problems which have been dominating the systematic uncertainty of the correlation analysis are related to this inconsistency. It is demonstrated that a new Coulomb correction method, based exclusively on the measured correlation function for π+π− pairs, may solve the problem.

Production of charged kaons in central S + S and O + Au collisions at 200 GeV/Nucleon

Abstract Product of charged kaons in central S + S and O + Au collisions at 200 GeV/nucleon has been studied in the NA 35 Streamer Chamber experiment. Mean multiplicities and transverse mass distributions were obtained. They were compared with nucleon-nucleon data and with model predictions.

A 50 × 50 CM2 rich detector prototype for ultrarelativistic heavy ion collisions

Abstract A 50 × 50 cm2 RICH detector was tested with hadron beams of 200 GeV/c to determine the resolution and efficiency of the system. Single photon detection has been achieved with a multistep avalanche chamber in conjunction with a CCD camera equipped with a 35 mm f 1.4 lens coupled to a two stage image intensifier. The results show that for the number of photons detected with the present setup and the geometry used in proximity focusing a standard deviation of 7.5 mrad per event has been achieved for the reconstruction of the Cherenkov angle.

Energy and rapidity dependence of the electric charge correlations at 20–158GeV beam energies at the CERN SPS (NA49)

Electric charge correlations are studied with the Balance Function method for central Pb + Pb collisions at the CERN — SPS. The results on centrality selected Pb + Pb interactions at 40 and 158 AGeV are presented for the first time for two different rapidity intervals:The mid‐rapidity region where a decrease of the width with increasing centrality of the collision is observed and the forward rapidity region where this effect vanishes. This could suggest a delayed hadronization scenario.In addition, the results from a first attempt to study the energy dependence of the Balance Function throughout the whole SPS energy range, will also be presented. The suitably scaled decrease of the width is approximately constant for the intermediate energies (30 to 80 AGeV) and gets stronger for the highest SPS and RHIC energies. On the other hand, both URQMD and HSD simulation results show no dependence on the collision energy.

Abnormal photonic energy — a signal of Quark matter possibly seen in exotic cosmic ray events

A phenomenological method is proposed to select possible Quark matter forming events in ultra-relativistic nucleus-nucleus interactions. We compare the released photonic and hadronic energies from a Quark matter forming event and from a normal Hadronic event and derive a relation, which may be used in an event-by-event analysis to differentiate the two phases. We determine thus two regions of QCD deconfinement. We also discuss the hadronic, photonic energy and multiplicity contents and the 〈PT〉 of several exotic cosmic ray events at ultra high energies. On the basis of the phenomenological model, we suggest that the “Centauro” type are Quark matter events near the projectile fragmentation region with very large baryochemical potential,μb. The “Anti-Centauro” type events are created by vacuum excitation in the central region with near zeroμb.

Using the Balance Function to study the charge correlations of hadrons

We present the recent Balance Function (BF) results obtained by the NA49 collaboration for the pseudo‐rapidity dependence of non‐identified charged particle correlations for two SPS energies. Experimental results indicate a clear centrality dependence only in the mid‐rapidity region. The results of an energy dependence study of the BF throughout the whole SPS energy range will also be discussed. In addition, the correlation of identified hadrons is studied and presented for the first time. The study of hadron correlation has also been extended in order to cope with the high multiplicity environment that is expected to be seen at LHC. We will present the latest results from simulations concerning the extension of these studies to the ALICE experiment.