2,194 research outputs found
Search for the QCD critical point in nuclear collisions at the CERN SPS
Pion production in nuclear collisions at the SPS is investigated with the aim
to search, in a restricted domain of the phase diagram, for power-laws in the
behavior of correlations which are compatible with critical QCD. We have
analyzed interactions of nuclei of different size (p+p, C+C, Si+Si, Pb+Pb) at
158 GeV adopting, as appropriate observables, scaled factorial moments in a
search for intermittent fluctuations in transverse dimensions. The analysis is
performed for pairs with invariant mass very close to the two-pion
threshold. In this sector one may capture critical fluctuations of the sigma
component in a hadronic medium, even if the -meson has no well defined
vacuum state. It turns out that for the Pb+Pb system the proposed analysis
technique cannot be applied without entering the invariant mass region with
strong Coulomb correlations. As a result the treatment becomes inconclusive in
this case. Our results for the other systems indicate the presence of power-law
fluctuations in the freeze-out state of Si+Si approaching in size the
prediction of critical QCD.Comment: 31 pages, 11 figure
Energy Dependence of Multiplicity Fluctuations in Heavy Ion Collisions at the CERN SPS
Multiplicity fluctuations of positively, negatively and all charged hadrons
in the forward hemisphere were studied in central Pb+Pb collisions at 20A, 30A,
40A, 80A and 158A GeV. The multiplicity distributions and their scaled
variances are presented in dependence of collision energy as well as of
rapidity and transverse momentum. The distributions have bell-like shape and
their scaled variances are in the range from 0.8 to 1.2 without any significant
structure in their energy dependence. No indication of the critical point in
fluctuations are observed. The string-hadronic model UrQMD significantly
overpredicts the mean, but approximately reproduces the scaled variance of the
multiplicity distributions. The predictions of the statistical hadron-resonance
gas model obtained within the grand-canonical and canonical ensembles disagree
with the measured scaled variances. The narrower than Poissonian multiplicity
fluctuations measured in numerous cases may be explained by the impact of
conservation laws on fluctuations in relativistic systems.Comment: 26 pages, 34 figures, updated version including referee comment
Upper Limit of D0 Production in Central Pb-Pb Collisions at 158A GeV
Results are presented from a search for the decays D0 -> Kmin piplus and
D0bar -> Kplus pimin in a sample of 3.8x10^6 central Pb-Pb events collected
with a beam energy of 158A GeV by NA49 at the CERN SPS. No signal is observed.
An upper limit on D0 production is derived and compared to predictions from
several models.Comment: REVTEX 5 pages, 4 figure
High p_T Spectra of Identified Particles Produced in Pb+Pb Collisions at 158GeV/nucleon Beam Energy
Transverse momentum spectra of pi^{+/-}, p, pbar, K^{+/-}, K^0_s and Lambda
at midrapidity were measured at high p_T in Pb+Pb collisions at 158GeV/nucleon
beam energy by the NA49 experiment. Particle yield ratios (p/pi, K/pi and
Lambda/K^0_s) show an enhancement of the baryon/meson ratio for p_T>2GeV/c. The
nuclear modification factor R_{CP} is extracted and compared to RHIC
measurements and pQCD calculations.Comment: Quark Matter 2005 parallel section proceeding
Bose-Einstein correlations of pion pairs in central Pb+Pb collisions at CERN SPS energies
Measurements of Bose-Einstein correlations of pion pairs in central Pb+Pb
collisions were performed with the NA49 detector at the CERN SPS for beam
energies of 20A, 30A, 40A, 80A, and 158A GeV. Correlation functions were
measured in the longitudinally co-moving ``out-side-long'' reference frame as a
function of rapidity and transverse momentum in the forward hemisphere of the
reaction. Radius and correlation strength parameters were obtained from fits of
a Gaussian parametrization. The results show a decrease of the radius
parameters with increasing transverse momentum characteristic of strong radial
flow in the pion source. No striking dependence on pion-pair rapidity or beam
energy is observed. Static and dynamic properties of the pion source are
obtained from simultaneous fits with a blast-wave model to radius parameters
and midrapidity transverse momentum spectra. Predictions of hydrodynamic and
microscopic models of Pb+Pb collisions are discussed.Comment: 22 pages, 23 figure
Electric charge fluctuations in central Pb+Pb collisions at 20, 30, 40, 80 and 158 AGeV
Results are presented on event-by-event electric charge fluctuations in
central Pb+Pb collisions at 20, 30, 40, 80 and 158 AGeV. The observed
fluctuations are close to those expected for a gas of pions correlated by
global charge conservation only. These fluctuations are considerably larger
than those calculated for an ideal gas of deconfined quarks and gluons. The
present measurements do not necessarily exclude reduced fluctuations from a
quark-gluon plasma because these might be masked by contributions from
resonance decays.Comment: 19 pages, 8 figure
Energy dependence of particle ratio fluctuations in central Pb+Pb collisions from ~6.3 to 17.3 GeV
We present measurements of the energy dependence of event-by-event
fluctuations in the K/pi and (p + \bar{p})/pi multiplicity ratios in heavy ion
collisions at the CERN SPS. The particle ratio fluctuations were obtained for
central Pb+Pb collisions at five collision energies, \sqrt{s_{_{NN}}}, between
6.3 and 17.3 GeV. After accounting for the effects of finite-number statistics
and detector resolution, we extract the strength of non-statistical
fluctuations at each energy. For the K/pi ratio, larger fluctuations than
expected for independent particle production are found at all collision
energies. The fluctuations in the (p + \bar{p})/pi ratio are smaller than
expectations from independent particle production, indicating correlated pion
and proton production from resonance decays. For both ratios, the deviation
from purely statistical fluctuations shows an increase towards lower collision
energies. The results are compared to transport model calculations, which fail
to describe the energy dependence of the K/pi ratio fluctuations.Comment: 11 pages, 10 figures, update to published versio
High p_T Spectra of Identified Particles Produced in Pb+Pb Collisions at 158A GeV Beam Energy
Results of the NA49 collaboration on the production of hadrons with large
transverse momentum in Pb+Pb collisions at 158A GeV beam energy are presented.
A range up to p_T = 4 GeV/c is covered. The nuclear modification factor R_CP is
extracted for pions, kaons and protons, and the baryon to meson ratios p/pi+,
pbar/pi- and Lambda/K^0_s are studied. All results are compared to other
measurements at SPS and RHIC and to theoretical calculations.Comment: Submitted to J. Phys. G (Proceedings of the 9th International
Conference on Strangeness in Quark Matter, Los Angeles, USA, March 26-31,
2006). 5 pages, 3 figure
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