J/Psi production as a function of charged particle multiplicity in pp collisions at sqrt{s}=7 TeV with the ALICE experiment

We report on the first measurement of J/Psi production as a function of charged particle pseudo-rapidity density dN_ch/d_eta in pp collisions at sqrt{s} = 7 TeV with the ALICE experiment at the LHC. J/Psi mesons are detected down to p_T = 0 via their decays into e+e- pairs at mid-rapidity (|y| < 0.9) and into mu+mu- pairs at forward rapidity (2.5<y<4). dN_ch/d_eta is measured within |eta| < 1. We compare results in the two different J/Psi rapidity ranges. Preliminary PYTHIA simulations are also presented.Comment: contribution to the MPI@LHC 2011 proceedings, 8 pages, 4 figure

Recent results from the ALICE experiment on open heavy flavours in hadronic collisions at the LHC

ALICE is the LHC experiment devoted to the study of the Quark-Gluon Plasma (QGP). To probe this high energy density state of strongly interacting matter expected to be produced in heavy-ion collisions at high energies, measurements performed in various systems (pp, p-Pb and Pb-Pb) are compared to each other. Heavy quarks are produced in initial hard partonic scatterings on a short time scale and participate in the subsequent evolution of the medium. This makes them sensitive probes of the QGP. With ALICE, open heavy flavours are studied using D mesons (D$^0$, D$^+$, D$^{*+}$) reconstructed via their hadronic decay channels in the mid-rapidity region ($|y|<0.5$) and with heavy-flavour decay leptons reconstructed in the electronic (muonic) channel in the central rapidity region $|y|<0.9$ (forward rapidity region $2.5<y<4$). We present ALICE measurements of the nuclear modification factor $R_{\rm{AA}}$ and the elliptic flow $v_2$ for D mesons and heavy-flavour decay leptons in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=2.76$ TeV. The corresponding measurements in p-Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ TeV are also discussed. First results on the azimuthal correlations between heavy-flavour particles and hadrons are presented as well as the charged-particle multiplicity dependence of heavy-flavour production in pp collisions at $\sqrt{s}=7$ TeV.Comment: Proceedings of 52nd International Winter Meeting on Nuclear Physics conference (Bormio 2014), 27-31 January 201

Collective flow in (anti)proton-proton collision at Tevatron and LHC

Collective flow as a consequence of hydrodynamical evolution in heavy ion collisions is intensively studied by theorists and experimentalists to understand the behavior of hot quark matter. Due to their large mass, heavy ions suffer collective effects even at low (SPS) or intermediate energies (RHIC). In case of light systems such as (anti)proton-proton interactions, collective effects was not expected. Within a global model such as EPOS, where light and heavy systems are treated using the same physics, it appears that Tevatron data are better described if a flow is introduced. Then the extrapolation to LHC can easily be done and we can compare to first data from ATLAS experiment.Comment: 4 pages, 6 figures, Proceeding of the 45th Rencontres de Moriond QC

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

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

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

Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at root(NN)-N-S=2.76 TeV

Peer reviewe

Elliptic flow of muons from heavy-flavour hadron decays at forward rapidity in Pb-Pb collisions at root s(NN)=2.76TeV

The elliptic flow, v(2), of muons from heavy-flavour hadron decays at forward rapidity (2.5 <y <4) is measured in Pb-Pb collisions at root s(NN)= 2.76TeVwith the ALICE detector at the LHC. The scalar product, two- and four-particle Q cumulants and Lee-Yang zeros methods are used. The dependence of the v(2) of muons from heavy-flavour hadron decays on the collision centrality, in the range 0-40%, and on transverse momentum, p(T), is studied in the interval 3 <p(T)<10 GeV/c. A positive v(2) is observed with the scalar product and two-particle Q cumulants in semi-central collisions (10-20% and 20-40% centrality classes) for the p(T) interval from 3 to about 5GeV/c with a significance larger than 3 sigma, based on the combination of statistical and systematic uncertainties. The v(2) magnitude tends to decrease towards more central collisions and with increasing pT. It becomes compatible with zero in the interval 6 <p(T)<10 GeV/c. The results are compared to models describing the interaction of heavy quarks and open heavy-flavour hadrons with the high-density medium formed in high-energy heavy-ion collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.Peer reviewe

Pseudorapidity and transverse-momentum distributions of charged particles in proton-proton collisions at root s=13 TeV

The pseudorapidity (eta) and transverse-momentum (p(T)) distributions of charged particles produced in proton-proton collisions are measured at the centre-of-mass energy root s = 13 TeV. The pseudorapidity distribution in vertical bar eta vertical bar <1.8 is reported for inelastic events and for events with at least one charged particle in vertical bar eta vertical bar <1. The pseudorapidity density of charged particles produced in the pseudorapidity region vertical bar eta vertical bar <0.5 is 5.31 +/- 0.18 and 6.46 +/- 0.19 for the two event classes, respectively. The transverse-momentum distribution of charged particles is measured in the range 0.15 <p(T) <20 GeV/c and vertical bar eta vertical bar <0.8 for events with at least one charged particle in vertical bar eta vertical bar <1. The evolution of the transverse momentum spectra of charged particles is also investigated as a function of event multiplicity. The results are compared with calculations from PYTHIA and EPOS Monte Carlo generators. (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