Heavy-flavour production and nuclear modification factor in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}}=2.76 TeV with ALICE

The measurement of heavy-flavour production and nuclear modification factor in heavy-ion collisions provides insights into the mechanisms of parton energy loss in the hot and dense medium formed in these collisions. ALICE results on heavy-flavour decay electrons and muons and on D mesons are presented.Comment: 5 pages, 7 figures, proceedings of the XXIV Quark Matter conference, May 19-24 2014, Darmstadt (Germany

Measurement of D-meson production in Pb-Pb collisions at the LHC with ALICE

The measurement of D-meson production in heavy-ion collisions at LHC energy provides insights into the mechanisms of interaction of charm quarks in the hot and dense medium formed in these collisions. ALICE results on the D-meson nuclear modification factor and azimuthal anisotropy in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV are presented

Measurement of the D0 meson production in Pb-Pb and p-Pb collisions with the ALICE experiment at the LHC

This thesis presents the measurement of the charmed D0 meson production relative to the reaction plane in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon collision of sqrt(sNN) = 2.76 TeV, and the measurement of the D0 production in p–Pb collisions at sqrt(sNN) = 5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. The D0 azimuthal anisotropy with respect to the reaction plane is sensitive to the interaction of the charm quarks with the high-density strongly-interacting medium formed in ultra-relativistic heavy-ion collisions and, thus, to the properties of this state of matter. In particular, this observable allows to establish whether low-momentum charm quarks participate in the collective expansion of the system and whether they can reach thermal equilibrium with the medium constituents. The azimuthal anisotropy is quantified in terms of the second coefficient v2 in a Fourier expansion of the D0 azimuthal distribution and in terms of the nuclear modification factor RAA, measured in the direction of the reaction plane and orthogonal to it. The measurement of the D0 production in p–Pb collisions is crucial to disentangle the effects induced by cold nuclear matter from the final state effects induced by the hot medium formed in Pb–Pb collisions. The D0 production is measured in both systems by reconstructing the two-prong hadronic decay D0 → K−π+ in the central rapidity region, exploiting the separation of the decay vertex from the primary vertex. The raw signal is obtained with an invariant mass analysis, and corrected for selection and reconstruction efficiency. A positive elliptic flow v2 is observed in Pb–Pb collisions in the centrality class 30–50%, with a mean value of 0.204 + 0.099 - 0.036 in the interval 2 < pT < 6 GeV/c, which decreases towards more central collisions. Consequently, the nuclear modification factor shows a stronger suppression in the direction orthogonal to the reaction plane. The v2 and the RAA measured in two azimuthal regions with respect to the reaction plane are compared to theoretical calculations of charm quark transport and energy loss in high-density strongly-interacting matter. The models that include substantial elastic interactions with an expanding medium provide a good description of the observed anisotropy. The D0 nuclear modification factor RpPb in p–Pb collisions is compatible with unity within uncertainties. The measured RpPb is compared to theoretical models including initial state effects, as well as to the nuclear modification factor measured in central Pb–Pb collisions. The D0 RpPb results are consistent with the modification of the nucleon parton distribution functions induced by the nuclear environment, and provide experimental evidence that the modification of the D meson momentum spectrum observed in Pb–Pb with respect to pp collisions is due to strong final state effects induced by the hot medium

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