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Adam, J.

Publications and source records attributed to Adam, J..

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Higher harmonic flow coefficients of identified hadrons in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76 $ TeV

The elliptic, triangular, quadrangular and pentagonal anisotropic flow coefficients for π ± , K ± and p + $\bar{p}$ in Pb-Pb collisions at √s NN =2.76 TeV were measured with the ALICE detector at the Large Hadron Collider. The results were obtained with the Scalar Product method, correlating the identified hadrons with reference particles from a different pseudorapidity region. Effects not related to the common event symmetry planes (non-flow) were estimated using correlations in pp collisions and were subtracted from the measurement. The obtained flow coefficients exhibit a clear mass ordering for transverse momentum (p T ) values below ≈ 3 GeV/c. In the intermediate p T region (3 < p T < 6 GeV/c), particles group at an approximate level according to the number of constituent quarks, suggesting that coalescence might be the relevant particle production mechanism in this region. The results for p T < 3 GeV/c are described fairly well by a hydrodynamical model (iEBE-VISHNU) that uses initial conditions generated by A Multi-Phase Transport model (AMPT) and describes the expansion of the fireball using a value of 0.08 for the ratio of shear viscosity to entropy density (η/s), coupled to a hadronic cascade model (UrQMD). Finally, expectations from AMPT alone fail to quantitatively describe the measurements for all harmonics throughout the measured transverse momentum region. However, the comparison to the AMPT model highlights the importance of the late hadronic rescattering stage to the development of the observed mass ordering at low values of p T and of coalescence as a particle production mechanism for the particle type grouping at intermediate values of p T for all harmonics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Centrality dependence of ψ(2S) suppression in p-Pb collisions at s N N = 5.02 $$ {\sqrt{s}}_{\mathrm{NN}}=5.02 $$ TeV

The inclusive production of the ψ(2S) charmonium state was studied as a function of centrality in p-Pb collisions at the nucleon-nucleon center of mass energy √ s NN = 5.02 TeV at the CERN LHC. The measurement was performed with the ALICE detector in the center of mass rapidity ranges -4.46 < y cms < -2.96 and 2.03 < y cms < 3.53, down to zero transverse momentum, by reconstructing the ψ(2S) decay to a muon pair. The ψ(2S) production cross section σ ψ(2S) is presented as a function of the collision centrality, which is estimated through the energy deposited in forward rapidity calorimeters. The relative strength of nuclear effects on the ψ(2S) and on the corresponding 1S charmonium state J/ψ is then studied by means of the double ratio of cross sections [σ ψ(2S) /σ J/ψ ] pPb /[σ ψ (2S) /σ J/ψ ] pp between p-Pb and pp collisions, and by the values of the nuclear modification factors for the two charmonium states. The results show a large suppression of ψ(2S) production relative to the J/ψ at backward (negative) rapidity, corresponding to the flight direction of the Pb-nucleus, while at forward (positive) rapidity the suppressions of the two states are comparable. Finally, comparisons to results from lower energy experiments and to available theoretical models are presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Differential studies of inclusive J/ψ and ψ(2S) production at forward rapidity in Pb-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=2.76 $ TeV

The production of J/ψ and ψ(2S) was studied with the ALICE detector in Pb-Pb collisions at the LHC. The measurement was performed at forward rapidity (2.5 < y < 4) down to zero transverse momentum (p t ) in the dimuon decay channel. Inclusive J/ψ yields were extracted in different centrality classes and the centrality dependence of the average p t is presented. The J/ψ suppression, quantified with the nuclear modification factor (R AA ), was measured as a function of centrality, transverse momentum and rapidity. Comparisons with similar measurements at lower collision energy and theoretical models indicate that the J/ψ production is the result of an interplay between color screening and recombination mechanisms in a deconfined partonic medium, or at its hadronization. Results on the ψ(2S) suppression are provided via the ratio of ψ(2S) over J/ψ measured in pp and Pb-Pb collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Centrality dependence of charged jet production in p–Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV

Measurements of charged jet production as a function of centrality are presented for p–Pb collisions recorded at $\sqrt{s_\mathrm{NN}}$= 5.02 TeV with the ALICE detector. Centrality classes are determined via the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon–nucleon collisions is determined based on the particle production in the Pb-going rapidity region. Jets have been reconstructed in the central rapidity region from charged particles with the anti-k T algorithm for resolution parameters R = 0.2 and R = 0.4 in the transverse momentum range 20 to 120 GeV/c. The reconstructed jet momentum and yields have been corrected for detector effects and underlying-event background. In the five centrality bins considered, the charged jet production in p–Pb collisions is consistent with the production expected from binary scaling from pp collisions. The ratio of jet yields reconstructed with the two different resolution parameters is also independent of the centrality selection, demonstrating the absence of major modifications of the radial jet structure in the reported centrality classes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Production of K $^{*}$ (892) $^{0}$ and $\phi $ (1020) in p–Pb collisions at $\sqrt{s_{{\text {NN}}}}$= 5.02 TeV

The production of K* (892) 0 and Φ(1020) mesons has been measured in p–Pb collisions at √s NN = 5.02 TeV. K * 0 and Φ are reconstructed via their decay into charged hadrons with the ALICE detector in the rapidity range - 0.5 < y < 0. The transverse momentum spectra, measured as a function of the multiplicity, have a p T range from 0 to 15 GeV/c for K* 0 and from 0.3 to 21 GeV/c for Φ. Integrated yields, mean transverse momenta and particle ratios are reported and compared with results in pp collisions at √s= 7 TeV and Pb–Pb collisions at √s NN = 2.76 TeV. In Pb–Pb and p–Pb collisions, K * 0 and Φ probe the hadronic phase of the system and contribute to the study of particle formation mechanisms by comparison with other identified hadrons. For this purpose, the mean transverse momenta and the differential proton-to-Φ ratio are discussed as a function of the multiplicity of the event. The short-lived K * 0 is measured to investigate re-scattering effects, believed to be related to the size of the system and to the lifetime of the hadronic phase.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Inclusive quarkonium production at forward rapidity in pp collisions at √s = 8 TeV

In this paper, we report on the inclusive production cross sections of J/ψ, ψ(2S), Υ(1S), Υ(2S) and Υ(3S), measured at forward rapidity with the ALICE detector in pp collisions at a center-of-mass energy √s = 8 TeV. The analysis is based on data collected at the LHC and corresponds to an integrated luminosity of 1.23 pb -1 . Quarkonia are reconstructed in the dimuon-decay channel. The differential production cross sections are measured as a function of the transverse momentum p T and rapidity y, over the p T ranges 0 < p T < 20 GeV/c for J/ψ, 0 < p T < 12 GeV/c for all other resonances, and for 2.5 < y < 4. The cross sections, integrated over p T and y, and assuming unpolarized quarkonia, are σ J/ψ = 8.98 ± 0.04 ± 0.82 μb, σ ψ(2S) = 1.23 ± 0.08 ± 0.22 μb, σ Υ(1S) = 71 ± 6 ± 7 nb, σ Υ(2S) = 26 ± 5 ± 4 nb and σ Υ(3S) = 9 ± 4 ± 1 nb, where the first uncertainty is statistical and the second one is systematic. These values agree, within at most 1.4σ, with measurements performed by the LHCb collaboration in the same rapidity range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at s NN = 2.76 TeV

Here, we report on results obtained with the event-shape engineering technique applied to Pb-Pb collisions at root √s NN = 2.76 TeV. By selecting events in the same centrality interval, but with very different average flow, different initial-state conditions can be studied. We find the effect of the event-shape selection on the elliptic flow coefficient v 2 to be almost independent of transverse momentum p T , which is as expected if this effect is attributable to fluctuations in the initial geometry of the system. Charged-hadron, -pion, -kaon, and -proton transverse momentum distributions are found to be harder in events with higher-than-average elliptic flow, indicating an interplay between radial and elliptic flow.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗