29 research outputs found
Femtoscopic scales in central A+A collisions at RHIC and LHC energies in hydrokinetic model
A study of the energy behavior of the interferometry radii is carried out for
the RHIC and LHC energies within the hydrokinetic model (HKM). The hydrokinetic
predictions for the HBT radii at LHC energies are compared with the recent
results of the ALICE Collaboration. The role of non-equilibrium and
non-hydrodynamic stage of the matter evolution in formation of the femtoscopy
scales at the LHC energies is analyzed. For this aim we develop the hybrid
hydrokinetic model.Comment: Talk presented by Yuri Sinyukov at "Quark Matter - 2011", May 23-28
2011, Annecy, France. 4 pages, 1 figur
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.
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
The CERES/NA45 Radial Drift Time Projection Chamber
The design, calibration, and performance of the first radial drift Time
Projection Chamber (TPC) are presented. The TPC was built and installed at the
CERES/NA45 experiment at the CERN SPS in the late nineties, with the objective
to improve the momentum resolution of the spectrometer. The upgraded experiment
took data twice, in 1999 and in 2000. After a detailed study of residual
distortions a spatial resolution of 340 um in the azimuthal and 640 um in the
radial direction was achieved, corresponding to a momentum resolution of Dp/p =
sqrt{(1% * p/GeV)^2 + (2%)^2}.Comment: 57 pages, 59 figure
Modification of jet-like correlations in Pb-Au collisions at 158A GeV/c
Results of a two-particle correlation analysis of high- charged
particles in Pb-Au collisions at 158 GeV/ are presented. The data have
been recorded by the CERES experiment at the CERN-SPS. The correlations are
studied as function of transverse momentum, particle charge and collision
centrality. We observe a jet-like structure in the vicinity of a high-
trigger particle and a broad back-to-back distribution. The yields of
associated particles per trigger show a strong dependence on the
trigger/associate charge combination. A comparison to PYTHIA confirms the
jet-like pattern at the near-side but suggests a strong modification at the
away-side, implying significant energy transfer of the hard-scattered parton to
the medium.Comment: 4 figure
Scale-dependence of transverse momentum correlations in Pb-Au collisions at 158A GeV/c
We present results on transverse momentum correlations of charged particle
pairs produced in Pb-Au collisions at 158 GeV/ at the Super Proton
Synchrotron. The transverse momentum correlations have been studied as a
function of collision centrality, angular separation of the particle pairs,
transverse momentum and charge sign. We demonstrate that the results are in
agreement with previous findings in scale-independent analyses at the same beam
energy. Employing the two-particle momentum correlator and the cumulative variable , we identify, using the
scale-dependent approach presented in this paper, different sources
contributing to the measured correlations, such as quantum and Coulomb
correlations, elliptic flow and mini-jet fragmentation.Comment: Revised versio
Transverse momentum spectra of charged particles in proton-proton collisions at GeV with ALICE at the LHC
The inclusive charged particle transverse momentum distribution is measured
in proton-proton collisions at GeV at the LHC using the ALICE
detector. The measurement is performed in the central pseudorapidity region
over the transverse momentum range GeV/.
The correlation between transverse momentum and particle multiplicity is also
studied. Results are presented for inelastic (INEL) and non-single-diffractive
(NSD) events. The average transverse momentum for is (stat.) (syst.) GeV/ and
\left_{\rm NSD}=0.489\pm0.001 (stat.) (syst.)
GeV/, respectively. The data exhibit a slightly larger than measurements in wider pseudorapidity intervals. The results are
compared to simulations with the Monte Carlo event generators PYTHIA and
PHOJET.Comment: 20 pages, 8 figures, 2 tables, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/390
Non-identical particle correlations in central Pb+Au collisions at 158 AGeV
Two-dimensional pion-proton correlation functions were analyzed in the central Pb+Au collision data taken by CERES at the top SPS energy. The correlations between the same- and the opposite-sign particles exhibit a minimum and a peak, respectively, at low relative momentum, caused by the mutual Coulomb interaction. The clearly visible asymmetry of the peak in the direction parallel to the pair momentum indicates that protons, on average, freeze-out at larger radii or at earlier times than pions. A similar result was obtained previously by the STAR experiment and was connected to the transverse flow. The high statistics of the CERES data set and the power of the two-dimensional analysis allow one to study how the observed displacement between the sources of pions and protons evolves with the transverse momentum