706 research outputs found
Particle Identification in the ALICE Experiment
The particle identification capabilities of the ALICE experiment are unique
among the four major LHC experiments. The working principles and excellent
performance of the central barrel detectors in a high-multiplicity environment
are presented as well as two physics examples: the extraction of transverse
momentum spectra of charged pions, kaons, protons, and the observation of the
anti-4He-nucleus.Comment: Quark Matter 2011 Proceeding
Confronting fluctuations of conserved charges in central nuclear collisions at the LHC with predictions from Lattice QCD
We construct net baryon number and strangeness susceptibilities as well as
correlations between electric charge and strangeness from experimental data of
the ALICE Collaboration at the CERN LHC. The data were taken in Pb-Pb
collisions at =2.76 TeV. The resulting fluctuations and
correlations are consistent with Lattice QCD results at the chiral crossover
pseudocritical temperature MeV. This agreement lends strong
support to the assumption that the fireball created in these collisions is of
thermal origin and exhibits characteristic properties expected in QCD at the
transition from the quark gluon plasma to the hadronic phase. The volume of the
fireball for one unit of rapidity at is found to exceed 4000 fm. A
detailed discussion on uncertainties in the temperature and volume of the
fireball is presented. The results are linked to pion interferometry
measurements and predictions from percolation theory.Comment: 7 pages, 4 figures Accepted for publication in PL
On coalescence as the origin of nuclei in hadronic collisions
The origin of weakly-bound nuclear clusters in hadronic collisions is a key
question to be addressed by heavy-ion collision (HIC) experiments. The measured
yields of clusters are approximately consistent with expectations from
phenomenological statistical hadronisation models (SHMs), but a theoretical
understanding of the dynamics of cluster formation prior to kinetic freeze out
is lacking. The competing model is nuclear coalescence, which attributes
cluster formation to the effect of final state interactions (FSI) during the
propagation of the nuclei from kinetic freeze out to the observer. This
phenomenon is closely related to the effect of FSI in imprinting femtoscopic
correlations between continuum pairs of particles at small relative momentum
difference. We give a concise theoretical derivation of the
coalescence--correlation relation, predicting nuclear cluster spectra from
femtoscopic measurements. We review the fact that coalescence derives from a
relativistic Bethe-Salpeter equation, and recall how effective quantum
mechanics controls the dynamics of cluster particles that are nonrelativistic
in the cluster centre of mass frame. We demonstrate that the
coalescence--correlation relation is roughly consistent with the observed
cluster spectra in systems ranging from PbPb to pPb and pp collisions. Paying
special attention to nuclear wave functions, we derive the coalescence
prediction for hypertriton and show that it, too, is roughly consistent with
the data. Our work motivates a combined experimental programme addressing
femtoscopy and cluster production under a unified framework. Upcoming pp, pPb
and peripheral PbPb data analysed within such a programme could stringently
test coalescence as the origin of clusters.Comment: 24 pages, 10 figure
Asynchronous coupling of hybrid models for efficient simulation of multiscale systems
We present a new coupling approach for the time advancement of multi-physics models of multiscale systems. This extends the method of E et al. (2009) [5] to deal with an arbitrary number of models. Coupling is performed asynchronously, with each model being assigned its own timestep size. This enables accurate long timescale predictions to be made at the computational cost of the short timescale simulation. We propose a method for selecting appropriate timestep sizes based on the degree of scale separation that exists between models. A number of example applications are used for testing and benchmarking, including a comparison with experimental data of a thermally driven rarefied gas flow in a micro capillary. The multiscale simulation results are in very close agreement with the experimental data, but are produced almost 50,000 times faster than from a conventionally-coupled simulation
Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV
Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe
Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC
Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe
Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions
We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe
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