Influence of Temperature and Humidity on Bakelite Resistivity

Presentation made at RPC99 and submitted to Elsevier PreprintThe use of phenolic or melaminic bakelite as RPC electrodes is widespread. The electrode resistivity is an important parameter for the RPC performance. As recent studies have pointed out, the bakelite resistivity changes with temperature and is influenced by humidity. In order to gain a quantitative understanding on the influence of temperature and humidity on RPC electrodes, we assembled an apparatus to measure resistivity in well-controlled conditions. A detailed description of the experimental set-up as well as the first resistivity measurements for various laminates in different environmental conditions are presented

Study of the Resistive Plate Chambers for the ALICE Dimuon Arm

Presentation made at RPC99 and submitted to Elsevier PreprintThe trigger system for the ALICE Dimuon Arm will be based on Resistive Plate Chambers. An RPC prototype, with electrodes made of low resistivity bakelite (rho ~ 3.109 Ωcm) has been tested both at the SPS and at the GIF. The results for operation in streamer mode are presented here

Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets

The multiplicity of inclusive photons has been measured on an event-by-event basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The systematics of the pseudorapidity densities at midrapidity (rho_max) and the width of the pseudorapidity distributions have been studied for varying centralities for these collisions. A power law fit to the photon yield as a function of the number of participating nucleons gives a value of 1.13+-0.03 for the exponent. The mean transverse momentum, , of photons determined from the ratio of the measured electromagnetic transverse energy and photon multiplicity, remains almost constant with increasing rho_max. Results are compared with model predictions.Comment: 16 pages including 4 figure

Scaling of Particle and Transverse Energy Production in 208Pb+208Pb collisions at 158 A GeV

Transverse energy, charged particle pseudorapidity distributions and photon transverse momentum spectra have been studied as a function of the number of participants (N_{part}) and the number of binary nucleon-nucleon collisions (N_{coll}) in 158 A GeV Pb+Pb collisions over a wide impact parameter range. A scaling of the transverse energy pseudorapidity density at midrapidity as N_{part}^{1.08 \pm 0.06} and N_{coll}^{0.83 \pm 0.05} is observed. For the charged particle pseudorapidity density at midrapidity we find a scaling as N_{part}^{1.07 \pm 0.04} and N_{coll}^{0.82 \pm 0.03}. This faster than linear scaling with N_{part} indicates a violation of the naive Wounded Nucleon Model.Comment: 13 pages, 16 figures, submitted to European Physical Journal C (revised results for scaling exponents

Freeze-Out Parameters in Central 158AGeV Pb+Pb Collisions

Neutral pion production in central 158AGeV Pb+Pb collisions has been studied in the WA98 experiment at the CERN SPS. The pi0 transverse mass spectrum has been analyzed in terms of a thermal model with hydrodynamic expansion. The high accuracy and large kinematic coverage of the measurement allow to limit previously noted ambiguities in the extracted freeze-out parameters. The results are shown to be sensitive to the shape of the velocity distribution at freeze-out.Comment: 5 pages including 3 figures, small changes due to review process, accepted for publication in Phys.Rev.Let

Direct Photon Production in 158 AGeV Pb+Pb Collisions

A measurement of direct photon production in Pb+Pb collisions at 158 AGeV has been carried out in the CERN WA98 experiment. The invariant yield of direct photons in central collisions is extracted as a function of transverse momentum in the interval 0.5 < pT < 4 GeV/c. A significant direct photon signal, compared to statistical and systematical errors, is seen at pT > 1.5 GeV/c. The results constitute the first observation of direct photons in ultrarelativistic heavy-ion collisions which could be significant for diagnosis of quark gluon plasma formation.Comment: Talk presented at Nucleus-Nucleus 2000, Strasbourg, Franc

Étude des chambres de trajectographie CPC du spectromètre dimuon d'ALICE

L'objectif de l'expérience ALICE est d'étudier le comportement de la matière nucléaire à de hautes densité et température, pour mettre en évidence une possible transition de phase de la matière hadronique vers un plasma de quarks et de gluons. Le spectromètre dimuon est un sous-détecteur d'ALICE. Son rôle est de détecter les paires de muons produites lors de la désintégration des résonances de saveurs lourdes dans les collisions d'ions lourds. La suppression de ces résonances est une des indications de la formation du plasma. Des tests sous faisceau ont été effectués au CERN, dans le but de valider le fonctionnement des chambres de trajectographie du spectromètre, vis-à-vis de la résolution spatiale et de l'efficacité. Une simulation détaillée de la réponse des chambres a été réalisée pour reproduire les données, et pour introduire l'effet des traces inclinées sur la résolution spatiale dans le code d'ALICE. Cet effet contribue à dégrader la résolution en masse des résonances.NANTES-BU Sciences (441092104) / SudocSTRASBOURG-Bib.Central Recherche (674822133) / SudocNANTES-ENS Mines (441092314) / SudocSudocFranceF