1,920 research outputs found
Solid-phase synthesis and crystal structure of 5(3-nitrophenyl)-3,7-diphenyl-4H,6H-1,2-diazepine
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Search for DCC in 158A GeV Pb+Pb Collisions
A detailed analysis of the phase space distributions of charged particles and
photons have been carried out using two independent methods. The results
indicate the presence of nonstatistical fluctuations in localized regions of
phase space.Comment: Talk at the PANIC99 Conference, June 9-16, 199
Particle density fluctuations
Event-by-event fluctuations in the multiplicities of charged particles and
photons at SPS energies are discussed. Fluctuations are studied by controlling
the centrality of the reaction and rapidity acceptance of the detectors.
Results are also presented on the event-by-event study of correlations between
the multiplicity of charged particles and photons to search for DCC-like
signals.Comment: Talk presented at Quark Matter 2002, Nantes, Franc
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
Pion Freeze-Out Time in Pb+Pb Collisions at 158 A GeV/c Studied via pi-/pi+ and K-/K+ Ratios
The effect of the final state Coulomb interaction on particles produced in
Pb+Pb collisions at 158 A GeV/c has been investigated in the WA98 experiment
through the study of the pi-/pi+ and K-/K+ ratios measured as a function of
transverse mass. While the ratio for kaons shows no significant transverse mass
dependence, the pi-/pi+ ratio is enhanced at small transverse mass values with
an enhancement that increases with centrality. A silicon pad detector located
near the target is used to estimate the contribution of hyperon decays to the
pi-/pi+ ratio. The comparison of results with predictions of the RQMD model in
which the Coulomb interaction has been incorporated allows to place constraints
on the time of the pion freeze-out.Comment: 9 pages, 12 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
Centrality Dependence of Neutral Pion Production in 158 A GeV Pb + Pb Collisions
The production of neutral pions in 158AGeV Pb+Pb collisions has been studied
in the WA98 experiment at the CERN SPS. Transverse momentum spectra are studied
for the range 0.3 GeV/c < mT-m0 < 4.0 GeV/c. The results for central collisions
are compared to various models. The centrality dependence of the neutral pion
spectral shape and yield is investigated. An invariance of the spectral shape
and a simple scaling of the yield with the number of participating nucleons is
observed for centralities with greater than about 30 participating nucleons
which is most naturally explained by assuming an equilibrated system.Comment: 5 pages, Latex, including 3 eps figures, submitted to Phys.Rev.Lett;
updated pQCD comparison due to new input from the author, updated references,
corrected plotting error in figure
Present Status and Future of DCC Analysis
Disoriented Chiral Condensates (DCC) have been predicted to form in high
energy heavy ion collisions where the approximate chiral symmetry of QCD has
been restored. This leads to large imbalances in the production of charged to
neutral pions. Sophisticated analysis methods are being developed to
disentangle DCC events out of the large background of events with
conventionally produced particles. We present a short review of current
analysis methods and future prospects.Comment: 12 pages, 5 figures. Invited talk presented at the 13th International
Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 97),
Tsukuba, Japan, 1-5 Dec 199
Event-by-Event Fluctuations in Particle Multiplicities and Transverse Energy Produced in 158.A GeV Pb+Pb collisions
Event-by-event fluctuations in the multiplicities of charged particles and
photons, and the total transverse energy in 158 GeV Pb+Pb collisions
are studied for a wide range of centralities. For narrow centrality bins the
multiplicity and transverse energy distributions are found to be near perfect
Gaussians. The effect of detector acceptance on the multiplicity fluctuations
has been studied and demonstrated to follow statistical considerations. The
centrality dependence of the charged particle multiplicity fluctuations in the
measured data has been found to agree reasonably well with those obtained from
a participant model. However for photons the multiplicity fluctuations has been
found to be lower compared to those obtained from a participant model. The
multiplicity and transverse energy fluctuations have also been compared to
those obtained from the VENUS event generator.Comment: To appear in Physical Review C; changes : more detailed discussion on
errors and few figures modifie
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