513 research outputs found
Prototype tests for the ALICE TRD
A Transition Radiation Detector (TRD) has been designed to improve the
electron identification and trigger capability of the ALICE experiment at the
Large Hadron Collider (LHC) at CERN. We present results from tests of a
prototype of the TRD concerning pion rejection for different methods of
analysis over a momentum range from 0.7 to 2 GeV/c. We investigate the
performance of different radiator types, composed of foils, fibres and foams.Comment: Presented at the IEEE Nuclear Science Symposium and Medical Imaging
Conference, Lyon, October 15-20, 2000 (accepted for publication in IEEE TNS),
Latex (IEEEtran.cls), 7 pages, 11 eps figure
Uranium on uranium collisions at relativistic energies
Deformation and orientation effects on compression, elliptic flow and
particle production in uranium on uranium collisions (UU) at relativistic
energies are studied within the transport model ART. The density compression in
tip-tip UU collisions is found to be about 30% higher and lasts approximately
50% longer than in body-body or spherical UU reactions. The body-body UU
collisions have the unique feature that the nucleon elliptic flow is the
highest in the most central collisions and remain a constant throughout the
reaction. We point out that the tip-tip UU collisions are more probable to
create the QGP at AGS and SPS energies while the body-body UU collisions are
more useful for studying properties of the QGP at higher energies.Comment: 8 pages + 4 figure
Hadron Correlations in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV with ALICE
Untriggered di-hadron correlations studies are shown which provide a map of
the bulk correlation structures in Pb-Pb collisions. Long-range correlations
are further studied by triggered correlations which address the dependence on
trigger and associated pT. Measured correlation functions are decomposed with a
multi-parameter fit and into Fourier coefficients. The jet-yield modification
factor I_AA is presented.Comment: Proceedings of plenary talk at the XXII International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 2011, Annec
Production of intermediate-mass dileptons in relativistic heavy ion collisions
The production of intermediate mass dileptons in ultrarelativistic nuclear
collisions at SPS energies is studied. The acceptance and detector resolution
inherent to measurements by the NA50 experimental collaboration are accurately
modeled. The measured centrality dependence of the intermediate mass lepton
pair excess is also addressed.Comment: 9 pages, 8 figures, ReVTe
Suppression of neutral pion production at large transverse momentum measured with the ALICE experiment in Pb-Pb collisions at TeV
The ALICE collaboration at the LHC has measured the transverse momentum
spectra of neutral pions via their two photon decay in pp and PbPb
collisions at TeV over a broad transverse momentum range
with different subsystems: with the electromagnetic calorimeters PHOS and EMCAL
and with photon conversions in the inner material of the detectors using
pairs reconstructed with the Central Tracking System. In this
report, neutral pions production is compared between pp and PbPb collisions
measured with conversion photons in terms of the nuclear modification factor,
, for different centrality selections of the PbPb data sample.Comment: 4 pages, 4 figures, proceedings of QM 201
Azimuthal dependence of pion source radii in Pb+Au collisions at 158 A GeV
We present results of a two-pion correlation analysis performed with the
Au+Pb collision data collected by the upgraded CERES experiment in the fall of
2000. The analysis was done in bins of the reaction centrality and the pion
azimuthal emission angle with respect to the reaction plane. The pion source,
deduced from the data, is slightly elongated in the direction perpendicular to
the reaction plane, similarly as was observed at the AGS and at RHIC.Comment: 5 pages, 2 figure
ALICE results from the first Pb-Pb run at the CERN LHC
After 20 years of preparation, the dedicated heavy ion experiment ALICE took
first data at the CERN LHC accelerator with proton collisions at the end of
2009 and with lead beams at the end of 2010. This article will give a brief
overview of the main results presented at the Quark Matter 2011 conference.Comment: Inited talk at the 22nd International Conference on
Ultra-relativistic Nucleus-Nucleus Collision (Quark Matter 2011), 23 - 28 May
2011, Annecy, Franc
The physics potential of proton-nucleus collisions at the TeV scale
The LHC brings nuclear collisions to the TeV scale for the first time and the
first data show the qualitative differences of this new regime. The
corresponding phase-space available encompasses completely uncharted regions of
QCD in which high-density or high-temperature domains can be identified.
Proton-nucleus runs are essential for a complete interpretation of the data and
for the study of new regimes dominated by large occupation numbers in the
hadronic wave function. I comment here the physics opportunities for p+Pb runs
at the LHC and d+Au runs at RHIC and the corresponding needs in view of the new
Pb+Pb data from the LHC.Comment: Proceedings of the conference Quark Matter 2011, Annecy (France) May
201
Particle identification in ALICE: a Bayesian approach
We present a Bayesian approach to particle identification (PID) within the ALICE experiment. The aim is to more effectively combine the particle identification capabilities of its various detectors. After a brief explanation of the adopted methodology and formalism, the performance of the Bayesian PID approach for charged pions, kaons and protons in the central barrel of ALICE is studied. PID is performed via measurements of specific energy loss () and time-of-flight. PID efficiencies and misidentification probabilities are extracted and compared with Monte Carlo simulations using high-purity samples of identified particles in the decay channels , , and in p-Pb collisions at TeV. In order to thoroughly assess the validity of the Bayesian approach, this methodology was used to obtain corrected spectra of pions, kaons, protons, and D mesons in pp collisions at TeV. In all cases, the results using Bayesian PID were found to be consistent with previous measurements performed by ALICE using a standard PID approach. For the measurement of D, it was found that a Bayesian PID approach gave a higher signal-to-background ratio and a similar or larger statistical significance when compared with standard PID selections, despite a reduced identification efficiency. Finally, we present an exploratory study of the measurement of in pp collisions at TeV, using the Bayesian approach for the identification of its decay products
Enhanced production of multi-strange hadrons in high-multiplicity proton-proton collisions
At sufficiently high temperature and energy density, nuclear matter undergoes a transition to a phase in which quarks and gluons are not confined: the quark-gluon plasma (QGP)(1). Such an exotic state of strongly interacting quantum chromodynamics matter is produced in the laboratory in heavy nuclei high-energy collisions, where an enhanced production of strange hadrons is observed(2-6). Strangeness enhancement, originally proposed as a signature of QGP formation in nuclear collisions(7), is more pronounced for multi-strange baryons. Several effects typical of heavy-ion phenomenology have been observed in high-multiplicity proton-proton (pp) collisions(8,9), but the enhanced production of multi-strange particles has not been reported so far. Here we present the first observation of strangeness enhancement in high-multiplicity proton-proton collisions. We find that the integrated yields of strange and multi-strange particles, relative to pions, increases significantly with the event charged-particle multiplicity. The measurements are in remarkable agreement with the p-Pb collision results(10,11), indicating that the phenomenon is related to the final system created in the collision. In high-multiplicity events strangeness production reaches values similar to those observed in Pb-Pb collisions, where a QGP is formed.Peer reviewe
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