53 research outputs found
Two-Proton Correlations near Midrapidity in p+Pb and S+Pb Collisions at the CERN SPS
Correlations of two protons emitted near midrapidity in p+Pb collisions at
450 GeV/c and S+Pb collisions at 200A GeV/c are presented, as measured by the
NA44 Experiment. The correlation effect, which arises as a result of final
state interactions and Fermi-Dirac statistics, is related to the space-time
characteristics of proton emission. The measured source sizes are smaller than
the size of the target lead nucleus but larger than the sizes of the
projectiles. A dependence on the collision centrality is observed; the source
size increases with decreasing impact parameter. Proton source sizes near
midrapidity appear to be smaller than those of pions in the same interactions.
Quantitative agreement with the results of RQMD (v1.08) simulations is found
for p+Pb collisions. For S+Pb collisions the measured correlation effect is
somewhat weaker than that predicted by the model simulations, implying either a
larger source size or larger contribution of protons from long-lived particle
decays.Comment: 10 pages (LaTeX) text, 4 (EPS) figures; accepted for publication in
Phys. Lett.
Strange Meson Enhancement in PbPb Collisions
The NA44 Collaboration has measured yields and differential distributions of
K+, K-, pi+, pi- in transverse kinetic energy and rapidity, around the
center-of-mass rapidity in 158 A GeV/c Pb+Pb collisions at the CERN SPS. A
considerable enhancement of K+ production per pi is observed, as compared to
p+p collisions at this energy. To illustrate the importance of secondary hadron
rescattering as an enhancement mechanism, we compare strangeness production at
the SPS and AGS with predictions of the transport model RQMD.Comment: 11 pages, including 4 figures, LATE
One and two dimensional analysis of 3pi correlations measured in Pb+Pb interactions
3pi- correlations from Pb+Pb collisions at 158 GeV/c per nucleon are
presented as measured by the focusing spectrometer of the NA44 experiment at
CERN. The three-body effect is found to be stronger for PbPb than for SPb. The
two-dimensional three-particle correlation function is also measured and the
longitudinal extension of the source is larger than the transverse extension
Two-kaon correlations in central Pb + Pb collisions at 158 A GeV/c
Two-particle interferometry of positive kaons is studied in Pb + Pb
collisions at mean transverse momenta and 0.91 GeV/c. A
three-dimensional analysis was applied to the lower data, while a
two-dimensional analysis was used for the higher data. We find that the
source size parameters are consistent with the scaling curve observed in
pion correlation measurements in the same collisions, and that the duration
time of kaon emission is consistent with zero within the experimental
sensitivity.Comment: 4 pages incl. 1 table and 3 fig's; RevTeX; accepted for publication
in PR
Antideuteron production in 158 AGeV/c Pb + Pb collisions
The invariant cross section as a function of transverse momentum for antideuterons produced in 158 A GeV/c per nucleon Pb+Pb central collisions has been measured by the NA44 experiment at CERN. This measurement, together with a measurement of antiprotons, allows for the determination of the antideuteron coalescence parameter. The extracted coalescence radius is found to agree with the deuteron coalescence radius and radii determined from two particle correlations. (27 refs)
Search for critical phenomena in Pb - Pb collisions
NA44 uses a 512 channel Si pad array covering to study charged hadron production in Pb+Pb collisions at the CERN SPS. We apply a multiresolution analysis, based on a Discrete Wavelet Transformation, to probe the texture of particle distributions event-by-event, by simultaneous localization of features in space and scale. Scanning a broad range of multiplicities, we look for a possible critical behaviour in the power spectra of local density fluctuations. The data are compared with detailed simulations of detector response, using heavy ion event generators, and with a reference sample created via event mixing.NA44 uses a 512 channel Si pad array covering to study charged hadron production in Pb+Pb collisions at the CERN SPS. We apply a multiresolution analysis, based on a Discrete Wavelet Transformation, to probe the texture of particle distributions event-by-event, by simultaneous localization of features in space and scale. Scanning a broad range of multiplicities, we look for a possible critical behaviour in the power spectra of local density fluctuations. The data are compared with detailed simulations of detector response, using heavy ion event generators, and with a reference sample created via event mixing
Identified Particle Elliptic Flow in Au+Au Collisions at GeV}
We report first results on elliptic flow of identified particles at
mid-rapidity in Au+Au collisions at GeV using the STAR
TPC at RHIC. The elliptic flow as a function of transverse momentum and
centrality differs significantly for particles of different masses. This
dependence can be accounted for in hydrodynamic models, indicating that the
system created shows a behavior consistent with collective hydrodynamical flow.
The fit to the data with a simple model gives information on the temperature
and flow velocities at freeze-out.Comment: REVTeX style include
Mid-rapidity anti-proton to proton ratio from Au+Au collisions at GeV
We report results on the ratio of mid-rapidity anti-proton to proton yields
in Au+Au collisions at \rts = 130 GeV per nucleon pair as measured by the
STAR experiment at RHIC. Within the rapidity and transverse momentum range of
and 0.4 1.0 GeV/, the ratio is essentially independent of
either transverse momentum or rapidity, with an average of for minimum bias collisions. Within errors, no
strong centrality dependence is observed. The results indicate that at this
RHIC energy, although the -\pb pair production becomes important at
mid-rapidity, a significant excess of baryons over anti-baryons is still
present.Comment: 5 pages, 3 figures, accepted by Phys. Rev. Let
Event texture search for phase transitions in Pb+Pb collisions
NA44 uses a 512-channel Si pad array covering 1.5<eta<3.3 to study charged hadron production in 158A GeV Pb+Pb collisions at the CERN SPS. We apply a multiresolution analysis, based on a discrete wavelet transformation, to probe the texture of particle distributions event by event, allowing a simultaneous localization of features in space and scale. Scanning a broad range of multiplicities, we search for signals of clustering and of critical behavior in the power spectra of local density fluctuations. The data are compared with detailed simulations of detector response, using heavy-ion event generators, and with a reference sample created via event mixing. An upper limit is set on the probability and magnitude of dynamical fluctuations
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