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The elliptic, triangular, quadrangular and pentagonal anisotropic flow coefficients for π ± , K ± and p+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.

Section: Scalar Product Methodsmentioning

confidence: 99%

“…The results are obtained with the Scalar Product method described in section 4, and in detail in refs. [23,[34][35][36]. In this article, the identified hadron under study and the charged reference particles are obtained from different, non-overlapping pseudorapidity regions.…”

Section: Jhep09(2016)164mentioning

confidence: 99%

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

Adam¹,

Adamová²,

Aggarwal³

et al. 2016

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“…Results corresponding to |∆η| > 1 (denoted with v n {2, |∆η| > 1}) are obtained with the two-particle cumulant correlating tracks from opposite sides of the TPC acceptance, −0.8 < η < −0.5 and 0.5 < η < 0.8. Results corresponding to |∆η| > 2 (and reported as v n {2, |∆η| > 2}) are obtained with the scalar product method [46], correlating all tracks at mid-rapidity (|η| < 0.8) with the n-th harmonic Q-vector Q V0A n calculated from the azimuthal distribution of the energy deposition measured in the V0A detector [2,47] …”

Section: Jhep07(2018)103mentioning

confidence: 99%

Energy dependence and fluctuations of anisotropic flow in Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ and 2.76 TeV

Acharya

Acosta

Adamová

et al. 2018

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Measurements of anisotropic flow coefficients with two-and multi-particle cumulants for inclusive charged particles in Pb-Pb collisions at √ s NN = 5.02 and 2.76 TeV are reported in the pseudorapidity range |η| < 0.8 and transverse momentum 0.2 < p T < 50 GeV/c. The full data sample collected by the ALICE detector in 2015 (2010), corresponding to an integrated luminosity of 12.7 (2.0) µb −1 in the centrality range 0-80%, is analysed. Flow coefficients up to the sixth flow harmonic (v 6 ) are reported and a detailed comparison among results at the two energies is carried out. The p T dependence of anisotropic flow coefficients and its evolution with respect to centrality and harmonic number n are investigated. An approximate power-law scaling of the form v n (p T ) ∼ p n/3 T is observed for all flow harmonics at low p T (0.2 < p T < 3 GeV/c). At the same time, the ratios v n /v n/m m are observed to be essentially independent of p T for most centralities up to about p T = 10 GeV/c. Analysing the differences among higher-order cumulants of elliptic flow (v 2 ), which have different sensitivities to flow fluctuations, a measurement of the standardised skewness of the event-by-event v 2 distribution P (v 2 ) is reported and constraints on its higher moments are provided. The Elliptic Power distribution is used to parametrise P (v 2 ), extracting its parameters from fits to cumulants. The measurements are compared to different model predictions in order to discriminate among initial-state models and to constrain the temperature dependence of the shear viscosity to entropy-density ratio.

“…The measurement of the elliptic flow with the scalar product method [66,67], a two particle correlation technique, is given by:…”

Section: Jhep09(2016)028mentioning

confidence: 99%

Elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity in Pb-Pb collisions at s N N = 2.76 $$ \sqrt{{\mathrm{s}}_{\mathrm{NN}}}=2.76 $$ TeV

Adam¹,

Adamová²,

Aggarwal³

et al. 2016

Self Cite

Abstract:The elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity (|y| < 0.7) is measured in Pb-Pb collisions at √ s NN = 2.76 TeV with ALICE at the LHC. The particle azimuthal distribution with respect to the reaction plane can be parametrized with a Fourier expansion, where the second coefficient (v 2 ) represents the elliptic flow. The v 2 coefficient of inclusive electrons is measured in three centrality classes (0-10%, 10-20% and 20-40%) with the event plane and the scalar product methods in the transverse momentum (p T ) intervals 0.5-13 GeV/c and 0.5-8 GeV/c, respectively. After subtracting the background, mainly from photon conversions and Dalitz decays of neutral mesons, a positive v 2 of electrons from heavy-flavour hadron decays is observed in all centrality classes, with a maximum significance of 5.9σ in the interval 2 < p T < 2.5 GeV/c in semicentral collisions (20-40%). The value of v 2 decreases towards more central collisions at low and intermediate p T (0.5 < p T < 3 GeV/c). The v 2 of electrons from heavy-flavour hadron decays at mid-rapidity is found to be similar to the one of muons from heavy-flavour hadron decays at forward rapidity (2.5 < y < 4). The results are described within uncertainties by model calculations including substantial elastic interactions of heavy quarks with an expanding strongly-interacting medium. The ALICE collaboration 34 Keywords: Heavy Ion Experiments IntroductionThe main goal of the ALICE [1] experiment is the study of strongly-interacting matter at the high energy density and temperature reached in ultra-relativistic heavy-ion collisions at the Large Hadron Collider (LHC). In these collisions the formation of a deconfined state of quarks and gluons, the Quark-Gluon Plasma (QGP), is predicted by Quantum ChromoDynamic (QCD) calculations on the lattice [2][3][4][5][6]. Because of their large masses, heavy quarks, i.e. charm (c) and beauty (b) quarks, are produced at the initial stage of the collision, almost exclusively in hard partonic scattering processes. Therefore, they interact with the medium in all phases of the system evolution, propagating through the hot and dense medium and losing energy via radiative [7,8] and collisional scattering [9][10][11] processes. Heavy-flavour hadrons and their decay products are thus effective probes to study the properties of the medium created in heavy-ion collisions. Heavy-quark energy loss in strongly-interacting matter can be studied via the modification of the transverse momentum (p T ) spectra of heavy-flavour hadrons and their decay products in heavy-ion collisions with respect to the proton-proton yield scaled by the number of binary nucleon-nucleon collisions, quantified by the nuclear modification factor (R AA ). A strong suppression of open charm hadrons and heavy-flavour decay leptons is observed for p T > 3 GeV/c in central collisions, both at RHIC ( √ s NN = 200 GeV) [12][13][14][15][16] -1 - JHEP09(2016)028and LHC ( √ s NN = 2.76 TeV) [17][18][19][20] energies. The PHENIX and STAR Collabor...