1,071 research outputs found
Nuclear Transparency in Heavy Ion Collisions at 14.6 GeV/nucleon
The probability of a projectile nucleon to traverse a target nucleus without
interaction is calculated for central Si-Pb collisions and compared to the data
of E814. The calculations are performed in two independent ways, via Glauber
theory and using the transport code UrQMD. For central collisions Glauber
predictions are about 30 to 50% higher than experiment, while the output of
UrQMD does not show the experimental peak of beam rapidity particles.Comment: 9 pages, 4 figures. submitted to Nucl. Phys.
Semi-Hard Scattering Unraveled from Collective Dynamics by Two-Pion Azimuthal Correlations in 158 A GeV/c Pb + Au Collisions
Elliptic flow and two-particle azimuthal correlations of charged hadrons and
high- pions ( 1 GeV/) have been measured close to mid-rapidity in
158A GeV/ Pb+Au collisions by the CERES experiment. Elliptic flow ()
rises linearly with to a value of about 10% at 2 GeV/. Beyond
1.5 GeV/, the slope decreases considerably, possibly indicating
a saturation of at high . Two-pion azimuthal anisotropies for
1.2 GeV/ exceed the elliptic flow values by about 60% in mid-central
collisions. These non-flow contributions are attributed to near-side and
back-to-back jet-like correlations, the latter exhibiting centrality dependent
broadening.Comment: Submitted to Phys. Rev. Letters, 4 pages, 5 figure
Low-mass e+e- pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum
We report a measurement of low-mass electron pairs observed in 158
GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of
invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4
(stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As
observed previously in S-Au collisions, the enhancement is most pronounced in
the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong
increase of the enhancement with centrality. In addition, we show that the
enhancement covers a wide range in transverse momentum, but is largest at the
lowest observed pt.Comment: 17 pages, 4 figures, submitted to Phys.Lett.
Leptonic and charged kaon decay modes of the meson measured in heavy-ion collisions at the CERN SPS
We report a measurement of meson production in central Pb+Au
collisions at E/A=158 GeV. For the first time in heavy-ion collisions,
mesons were reconstructed in the same experiment both in the KK
and the dilepton decay channel. Near mid-rapidity, this yields rapidity
densities, corrected for production at the same rapidity value, of 2.05 +-
0.14(stat) +- 0.25(syst) and 2.04 +- 0.49(stat)+-{0.32}(syst), respectively.
The shape of the measured transverse momentum spectra is also in close
agreement in both decay channels. The data rule out a possible enhancement of
the yield in the leptonic over the hadronic channel by a factor larger
than 1.6 at 95% CL.Comment: 11 pages, 4 figures,submitted to Phys. Rev. Let
Recent results from Pb-Au collisions at 158 GeV/c per nucleon obtained with the CERES spectrometer
During the 1996 lead run time, CERES has accumulated 42 million events,
corresponding to a factor of 5 more statistics than in 1995 and 2.5 million
events of a special photon-run. We report on the results of the low-mass
ee-pair analysis. Since the most critical item is the poor
signal-to-background ratio we also discuss the understanding of this
background, in absolute terms, with the help of a detailed Monte Carlo
simulation. We show preliminary results of the photon analysis and summarize
the results of the hadron analysis preliminarily reported on already at QM'97Comment: 10 pages, 9 figures, Proceedings of the XIV Int. Conf. on
Nucleus-Nucleus Collisions,Quark Matter 99, Torino, Italy, May 10 - 15, 199
Elliptic flow of charged pions, protons and strange particles emitted in Pb+Au collisions at top SPS energy
Differential elliptic flow spectra v2(pT) of \pi-, K0short, p, \Lambda have
been measured at \sqrt(s NN)= 17.3 GeV around midrapidity by the
CERN-CERES/NA45 experiment in mid-central Pb+Au collisions (10% of
\sigma(geo)). The pT range extends from about 0.1 GeV/c (0.55 GeV/c for
\Lambda) to more than 2 GeV/c. Protons below 0.4 GeV/c are directly identified
by dE/dx. At higher pT, proton elliptic flow v2(pT) is derived as a
constituent, besides \pi+ and K+, of the elliptic flow of positive pion
candidates. The retrieval requires additional inputs: (i) of the particle
composition, and (ii) of v2(pT) of positive pions. For (i), particle ratios
obtained by NA49 were adapted to CERES conditions; for (ii), the measured
v2(pT) of negative pions is substituted, assuming \pi+ and \pi- elliptic flow
magnitudes to be sufficiently close. The v2(pT) spectra are compared to
ideal-hydrodynamics calculations. In synopsis of the series \pi- - K0short - p
- \Lambda, flow magnitudes are seen to fall with decreasing pT progressively
even below hydro calculations with early kinetic freeze-out (Tf= 160 MeV)
leaving not much time for hadronic evolution. The proton v2(pT) data show a
downward swing towards low pT with excursions into negative v2 values. The
pion-flow isospin asymmetry observed recently by STAR at RHIC, invalidating in
principle our working assumption, is found in its impact on proton flow
bracketed from above by the direct proton flow data, and not to alter any of
our conclusions. Results are discussed in perspective of recent viscous
dynamics studies which focus on late hadronic stages.Comment: 38 pages, 27 figures, 2 tables. Abstract and parts of introduction
made more comprehensible; corrected typos; acknowledgement added. To appear
in Nucl.Phys.
Lambda production in 40 A GeV/c Pb-Au collisions
During the 1999 lead run, CERES has measured hadron and electron-pair
production at 40 A GeV/c beam momentum with the spectrometer upgraded by the
addition of a radial TPC. Here the analysis of lambda and antilambda will be
presented.Comment: 8 pages, 8 figures. 6th International Conference on Strange Quarks in
Matter, Frankfurt 200
Flow and non-flow event anisotropies at the SPS
A study of differential elliptic event anisotropies (v_2) of charged
particles and high-pt pions in 158 AGeV/c Pb+Au collisions is presented.
Results from correlations with respect to the event plane and from two-particle
azimuthal correlations are compared. The latter give systematically higher v_2
values at pt>1.2GeV/c providing possibly an evidence of a non-flow semihard
component.Comment: 4 pages, 6 figures, Quark Matter 2002, Nantes, to appear in Nucl.
Phys.
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