37 research outputs found
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
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
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
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
Solving a Deconvolution Problem in Photon Spectrometry
We solve numerically a deconvolution problem to extract the undisturbed spectrum from the measured distribution contaminated by the finite resolution of the measuring device. A problem of this kind emerges when one wants to infer the momentum distribution of the neutral pions by detecting the it decay photons using the photon spectrometer of the ALICE LHC experiment at CERN {[}1]. The underlying integral equation connecting the sought for pion spectrum and the measured gamma spectrum has been discretized and subsequently reduced to a system of linear algebraic equations. The latter system, however, is known to be ill-posed and must be regularized to obtain a stable solution. This task has been accomplished here by means of the Tikhonov regularization scheme combined with the L-curve method. The resulting pion spectrum is in an excellent quantitative agreement with the pion spectrum obtained from a Monte Carlo simulation. (C) 2010 Elsevier B.V. All rights reserved
Direct photons in WA98
A measurement of direct photon production in /sup 208/Pb+/sup 208/Pb collisions at 158 A GeV has been carried out in the CERN WA98 experiment. The invariant yield of direct photons was extracted as a function of transverse momentum in the interval 0.51.5 GeV/c. the result constitutes the first observation of direct photons in ultrarelativistic heavy-ion collisions. (19 refs)
production in 158 A GeV interactions at the CERN SPS
The Delta /sup ++/-resonance production in central 158 A GeV /sup 208 /Pb+/sup 208/Pb collisions at the CERN SPS has been studied. The Delta /sup ++/ production was estimated from the invariant mass spectrum of p pi /sup +/-pairs by subtracting a mixed event background. The measured Delta /sup ++/ abundance is compared with the results from other experiments at lower energies, and with a model calculation assuming thermal and chemical equilibrium. (19 refs)