75 research outputs found
Multi-strange baryon measurements at LHC energies, with the ALICE experiment
The status of the charged multi-strange baryon analysis (Xi-, anti-Xi+,
Omega-, anti-Omega+) at LHC energies is presented. This report is based on the
results obtained with ALICE (A Large Ion Collider Experiment), profiting from
the characteristic cascade-decay topology. A special attention is drawn to the
early pp data-taking period (2009-2010) and subsequently, on the uncorrected
pT-spectra extracted at mid-rapidity for centre of mass energies of 0.9 TeV and
7 TeV.Comment: 4 pages, 5 figures, Hot Quarks 2010 proceedings, La Londe Les Maures,
France, June 2010 (to be published in Journal of Physics: Conference Series
Correlations and fluctuations studied with ALICE
The measurement of particle correlations and event-by-event fluctuations of
physical observables allows to study a large variety of properties of the
matter produced in ultra relativistic heavy-ion collisions. We will present
results for two-particle correlations, mean transverse momentum fluctuations,
and net charge fluctuations in Pb-Pb collisions at 2.76 TeV.Comment: 7 pages, 5 figures, Proceedings submitted for the 28th Winter
Workshop on Nuclear Dynamics, Puerto Rico, April 7-14, 2012; corrected typo
Cross section normalization in proton-proton collisions at = 2.76 TeV and 7 TeV, with ALICE at LHC
Measurements of the cross sections of the reference processes seen by the
ALICE trigger system were obtained based on beam properties measured from van
der Meer scans. The measurements are essential for absolute cross section
determinations of physics processes.
The paper focuses on instrumental and technical aspects of detectors and
accelerators, including a description of the extraction of beam properties from
the van der Meer scan. As a result, cross sections of reference processes seen
by the ALICE trigger system are given for proton-proton collisions at two
energies; =2.76 TeV and 7 TeV, together with systematic uncertainties
originating from beam intensity measurements and other detector effects.
Consistency checks were performed by comparing to data from other experiments
in LHC.Comment: Quark Matter 2011 Conference Proceedings, 4 pages, 2 figure
Two particle correlations: a probe of the LHC QCD medium
The properties of --jet pairs emitted in heavy-ion collisions provide
an accurate mean to perform a tomographic measurement of the medium created in
the collision through the study of the medium modified jet properties. The idea
is to measure the distribution of hadrons emitted on the opposite side of the
%oppositely by tagging the direct photon. The feasibility of such measurements
is studied by applying the approach on the simulation data, we have
demonstrated that this method allows us to measure, with a good approximation,
both the jet fragmentation and the back-to-back azimuthal alignment of the
direct photon and the jet. Comparing these two observables measured in pp
collisions with the ones measured in AA collisions reveals the modifications
induced by the medium on the jet structure and consequently allows us to infer
the medium properties. In this contribution, we discuss a first attempt of such
measurements applied to real proton-proton data from the ALICE experiment.Comment: 4 pages, 4 figures, Proceedings for Hot Quark 2010 Conferenc
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
Measurement of heavy-flavor production in Pb-Pb collisions at the LHC with ALICE
A Large Ion Collider Experiment (ALICE) at the Large Hadron Collider (LHC)
has been built in order to study the Quark-Gluon Plasma (QGP) created in
high-energy nuclear collisions. As heavy-flavor quarks are produced at the
early stage of the collision, they serve as sensitive probes for the QGP. The
ALICE detector with its capabilities such as particle identification, secondary
vertexing and tracking in a high multiplicity environment can address, among
other measurements, the heavy-flavor sector in heavy-ion collisions. We present
latest results on the measurement of the nuclear modification factor of open
heavy-flavors as well as on the measurement of open heavy-flavor azimuthal
anisotropy v2 in Pb-Pb collisions at sqrt(s) = 2.76 TeV. Open charmed hadrons
are reconstructed in the hadronic decay channels D0->Kpi, D+->Kpipi, and
D*+->D0pi applying a secondary decay-vertex topology. Complementary
measurements are performed by detecting electrons (muons) from semi-leptonic
decays of open heavy-flavor hadrons in the central (forward) rapidity region.Comment: 10 pages, 6 figures. Talk given by Robert Grajcarek at the 11th
International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio,
Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in
Journal of Physics: Conference Series (JPCS
K0s-K0s correlations in 7 TeV pp collisions from the ALICE experiment at the LHC
Identical neutral kaon pair correlations are measured in 7 TeV pp collisions
in the ALICE experiment. K0s-K0s correlation functions are formed in 3
multiplicity X 4 kT bins. The femtoscopic kaon source parameters Rinv and
lambda are extracted from these correlation functions by fitting a (femtoscopy)
X (PYTHIA) model to them, PYTHIA accounting for the non-flat baseline found in
pp collisions. Source parameters are obtained from a fit which includes quantum
statistics and final-state interactions of the a0/f0 resonance. K0s-K0s
correlations show a systematic increase in Rinv for increasing multiplicity bin
and decreasing Rinv for increasing kT bin as seen in pi-pi correlations in the
pp system, as well as seen in heavy-ion collisions. Also, K0s-K0s correlations
are observed to smoothly extend this pi-pi Rinv behavior for the pp system up
to about three times higher kT than the kT range measured in pi-pi
correlations.Comment: Proceedings of the Quark Matter 2011 Conference, 4 pages, 5 figure
Charged particle jet measurements with the ALICE experiment in proton-proton collisions at the LHC
We present preliminary results of measurements of charged particle jet
properties in proton-proton collisions at = 7 TeV using the ALICE
detector. Jets are reconstructed using and SISCone jet
finding algorithms with resolution parameter in the range of transverse
momentum from 20 to 100 GeV/ in the midrapidity region
(\mid\eta\mid\textless 0.5). The uncorrected charged jet spectra obtained
using the three different jet finders show good agreement. The data are
compared to predictions from PYTHIA-Perugia0, PYTHIA-Perugia2011, and PHOJET.
The mean charged particle multiplicity in leading jets increases with
increasing jet and is consistent with model predictions. The radial
distributions of transverse momentum about the jet direction and the
distributions of the average radius containing 80% of the total jet
found in the jet cone ( in this analysis), indicate that high jets are more collimated than low jets.Comment: 6 pages, 6 figures, Conference Proceedings submitted for the 28th
Winter Workshop on Nuclear Dynamics, Puerto Rico, April 7-14, 201
Triggered di-hadron correlations in Pb--Pb collisions from the ALICE experiment
Angular correlations between unidentified hadron trigger and associated
particles are measured by the ALICE experiment for GeV,
where \ptt \geq \pta. The pair correlation shapes are examined in a variety
of centrality categories for pairs in . A series of two-particle Fourier components are extracted from the long-range azimuthal correlation
functions. The sum of terms match the data. For each , a fit is
applied over all bins simultaneously to test the collectivity
hypothesis . The factorization holds at
below approximately 4 GeV but breaks progressively at higher
momenta. The divergence between the data and the global fit quantifies the
onset of nonflow dominance in long-range correlations due to the away side jet.
The values from the global fit are in close agreement with results from
more established methods. At higher \pt where jet correlations dominate, the
modification of conditional yields in central Pb--Pb collisions is measured
with respect to () and with respect to peripheral events
(). Significant suppression is observed on the side opposing the
trigger, while a moderate enhancement is measured on the near side
Event-by-event mean p_T fluctuations in pp and Pb-Pb collisions measured by the ALICE experiment at the LHC
Non-statistical event-by-event fluctuations of the mean transverse momentum
of charged particles in pp and Pb-Pb collisions are studied using the ALICE
experiment at the LHC. Little collision energy dependence is observed in pp.
The data indicate a common scaling behaviour with event multiplicity from pp to
semi-central Pb-Pb collisions. In central Pb-Pb, the results deviate from this
trend, exhibiting a significant reduction of the fluctuation strength. The
results are compared with measurements in Au-Au collisions at lower energies
and with Monte Carlo simulations.Comment: 4 pages, 3 figures, proceedings to Quark Matter 2011; only minor
changes in the new version (e.g. description of error bars of fig.3 in more
detail, ref.5 updated), figures not changed, this is the published versio
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