Measurement of the nuclear modification factor of electrons from heavy-flavour decays at mid-rapidity in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV with ALICE

We present results on inclusive electrons for 1.5 $< p_{\rm T} <$ 6 GeV/$c$ in {Pb-Pb} collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV measured with ALICE at the LHC and compare these to a cocktail of background electron sources. The excess of electrons beyond the cocktail at high momenta ({$p_{\rm T} >$ 3.5 GeV/$c$}) is attributed to electrons from heavy-flavour decays. The corresponding nuclear modification factor indicates heavy-flavour suppression by a factor of 1.5-4.Comment: 4 pages; 4 figures; QM 2011 proceeding

Neutral Pions and Eta Mesons as Probes of the Hadronic Fireball in Nucleus-Nucleus Collisions around 1A GeV

Chemical and thermal freeze-out of the hadronic fireball formed in symmetric collisions of light, intermediate-mass, and heavy nuclei at beam energies between 0.8A GeV and 2.0A GeV are discussed in terms of an equilibrated, isospin-symmetric ideal hadron gas with grand-canonical baryon-number conservation. For each collision system the baryochemical potential mu_B and the chemical freeze-out temperature T_c are deduced from the inclusive neutral pion and eta yields which are augmented by interpolated data on deuteron production. With increasing beam energy mu_B drops from 800 MeV to 650 MeV, while T_c rises from 55 MeV to 90 MeV. For given beam energy mu_B grows with system size, whereas T_c remains constant. The centrality dependence of the freeze-out parameters is weak as exemplified by the system Au+Au at 0.8A GeV. For the highest beam energies the fraction of nucleons excited to resonance states reaches freeze-out values of nearly 15 %, suggesting resonance densities close to normal nuclear density at maximum compression. In contrast to the particle yields, which convey the status at chemical freeze-out, the shapes of the related transverse-mass spectra do reflect thermal freeze-out. The observed thermal freeze-out temperatures T_th are equal to or slightly lower than T_c, indicative of nearly simultaneous chemical and thermal freeze-out.Comment: 42 pages, 12 figure

An assessment of J/Psi formation in the light of initial RHIC data

Predictions of J/Psi formation at RHIC via "off-diagonal" combinations of charm and anticharm quarks in a region of color deconfinement are confronted with initial data from the PHENIX collaboration. We find that the measured centrality behavior places significant constraints on the various parameters which control model calculations of J/Psi formation. Within present statistical and systematic uncertainties, one can map out a region of parameter space within which the contribution of formation in a deconfined phase is allowed. As these uncertainties decrease and new data from d-Au interactions becomes available, it is expected that definitive tests for the presence of this formation mechanism will be possible. We anticipate that the rapidity and transverse momentum spectra will prove decisive for a final determination.Comment: 6 pages, 5 figures, presented at SQM2003, March 12-17, 2003. To be published in J. Phys.

D meson nuclear modification factors in Pb-Pb collisions at {\surd}sNN = 2.76 TeV, measured with the ALICE detector

The ALICE experiment has measured the D meson production in pp and Pb-Pb collisions at the LHC at {\surd}s = 7 and 2.76 TeV and {\surd}sNN = 2.76 TeV respectively, via the exclusive reconstruction of hadronic decay channels. The analyses of the D0{\to}K-pi+ and D+{\to}K-pi+pi+ channels will be described and the preliminary results for the D0 and D+ nuclear modification factor will be presented.Comment: Proceedings of Quark Matter 2011 conference. 4 pages, 4 figures. The slides of the talk can be found at the link: http://indico.cern.ch/materialDisplay.py?contribId=591&sessionId=53&materialId=slides&confId=3024

Heavy-flavour production in Pb-Pb collisions at the LHC, measured with the ALICE detector

We present the first results from the ALICE experiment on the nuclear modification factors for heavy-flavour hadron production in Pb-Pb collisions at sqrt{s_NN}=2.76 TeV. Using proton-proton and lead-lead collision samples at sqrt{s}=7 TeV and sqrt{s_NN}=2.76 TeV, respectively, nuclear modification factors R_AA(pt) were measured for D mesons at central rapidity (via displaced decay vertex reconstruction), and for electrons and muons, at central and forward rapidity, respectively.Comment: 8 pages, 5 figures, plenary talk at Quark Matter 2011, Annecy, Franc

Reinforcement learning in populations of spiking neurons

Population coding is widely regarded as a key mechanism for achieving reliable behavioral responses in the face of neuronal variability. But in standard reinforcement learning a flip-side becomes apparent. Learning slows down with increasing population size since the global reinforcement becomes less and less related to the performance of any single neuron. We show that, in contrast, learning speeds up with increasing population size if feedback about the populationresponse modulates synaptic plasticity in addition to global reinforcement. The two feedback signals (reinforcement and population-response signal) can be encoded by ambient neurotransmitter concentrations which vary slowly, yielding a fully online plasticity rule where the learning of a stimulus is interleaved with the processing of the subsequent one. The assumption of a single additional feedback mechanism therefore reconciles biological plausibility with efficient learning

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

The Vector Probe in Heavy-Ion Reactions

We review essential elements in using the $J^P=1^-$ channel as a probe for hot and dense matter as produced in (ultra-) relativistic collisions of heavy nuclei. The uniqueness of the vector channel resides in the fact that it directly couples to photons, both real and virtual (dileptons), enabling the study of thermal radiation and in-medium effects on both light ($\rho, \omega, \phi$) and heavy ($\Psi, \Upsilon$) vector mesons. We emphasize the importance of interrelations between photons and dileptons, and characterize relevant energy/mass regimes through connections to Quark-Gluon-Plasma emission and chiral symmetry restoration. Based on critical analysis of our current understanding of data from fixed-target energies, we identify open key questions to be addressed.Comment: Invited Talk at the Hot Quarks 2004 Workshop, July 18-24, 2004 (Taos Valley, NM, USA), 15 pages latex incl 14 figs and iop style files, to appear in the proceeding