52 research outputs found
Event-by-event fluctuations at SPS
Results on event-by-event fluctuations of the mean transverse momentum and
net charge in Pb-Au collisions, measured by the CERES Collaboration at
CERN-SPS, are presented. We discuss the centrality and beam energy dependence
and compare our data to cascade calculations.Comment: 4 pages, 4 figures, proceedings to INPC2004 Goteborg, Swede
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.
Transition Radiation Spectroscopy with Prototypes of the ALICE TRD
We present measurements of the transition radiation (TR) spectrum produced in
an irregular radiator at different electron momenta. The data are compared to
simulations of TR from a regular radiator.Comment: 4 pages, 5 Figures, Proceedings for "TRDs for the 3rd millennium"
(Sept. 4-7, 2003, Bari, Italy
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
Energy loss of pions and electrons of 1 to 6 GeV/c in drift chambers operated with Xe,CO2(15%)
We present measurements of the energy loss of pions and electrons in drift
chambers operated with a Xe,CO2(15%) mixture. The measurements are carried out
for particle momenta from 1 to 6 GeV/c using prototype drift chambers for the
ALICE TRD. Microscopic calculations are performed using input parameters
calculated with GEANT3. These calculations reproduce well the measured average
and most probable values for pions, but a higher Fermi plateau is required in
order to reproduce our electron data. The widths of the measured distributions
are smaller for data compared to the calculations. The electron/pion
identification performance using the energy loss is also presented.Comment: 15 pages, 10 figures, accepted for publication in Nucl.Instrum.Meth.
Space charge in drift chambers operated with the Xe,CO2(15%) mixture
Using prototype modules of the ALICE Transition Radiation Detector we
investigate space charge effects and the dependence of the pion rejection
performance on the incident angle of the ionizing particle. The average pulse
height distributions in the drift chambers operated with the Xe,CO2(15%)
mixture provide quantitative information on the gas gain reduction due to space
charge accumulating during the drift of the primary ionization. Our results
demonstrate that the pion rejection performance of a TRD is better for tracks
which are not at normal incidence to the anode wires. We present detailed
simulations of detector signals, which reproduce the measurements and lend
strong support to our interpretation of the measurements in terms of space
charge effects.Comment: 18 pages, 10 figures, accepted for publication in Nucl.Instrum.Meth.
A. Data files available at http://www-alice.gsi.de/tr
Event-by-event fluctuations of the mean transverse momentum in 40, 80, and 158 A GeV/c Pb-Au collisions
Measurements of event-by-event fluctuations of the mean transverse momentum
in Pb-Au collisions at 40, 80, and 158 A GeV/c are presented. A significant
excess of mean p_T fluctuations at mid-rapidity is observed over the
expectation from statistically independent particle emission. The results are
somewhat smaller than recent measurements at RHIC. A possible non-monotonic
behaviour of the mean p_T fluctuations as function of collision energy, which
may have indicated that the system has passed the critical point of the QCD
phase diagram in the range of mu_B under investigation, has not been observed.
The centrality dependence of mean p_T fluctuations in Pb-Au is consistent with
an extrapolation from pp collisions assuming that the non-statistical
fluctuations scale with multiplicity. The results are compared to calculations
by the RQMD and UrQMD event generators.Comment: 28 pages, 10 figure
Universal Pion Freeze-out in Heavy-Ion Collisions
Based on an evaluation of data on pion interferometry and on particle yields
at mid-rapidity, we propose a universal condition for thermal freeze-out of
pions in heavy-ion collisions. We show that freeze-out occurs when the mean
free path of pions lambda_f reaches a value of about 1 fm, which is much
smaller than the spatial extent of the system at freeze-out. This critical mean
free path is independent of the centrality of the collision and beam energy
from AGS to RHIC.Comment: 5 pages, 3 figures, revised version resubmitted to PR
Position Reconstruction in Drift Chambers operated with Xe, CO2 (15%)
We present measurements of position and angular resolution of drift chambers
operated with a Xe,CO(15%) mixture. The results are compared to Monte Carlo
simulations and important systematic effects, in particular the dispersive
nature of the absorption of transition radiation and non-linearities, are
discussed. The measurements were carried out with prototype drift chambers of
the ALICE Transition Radiation Detector, but our findings can be generalized to
other drift chambers with similar geometry, where the electron drift is
perpendicular to the wire planes.Comment: 30 pages, 18 figure
The ALICE experiment at the CERN LHC
ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries. Its overall dimensions are 161626 m3 with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008
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