Browsing by Subject "ELLIPTIC FLOW"

Sort by: Order: Results:

Now showing items 1-8 of 8
  • The ALICE collaboration; Acharya, S.; Brücken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2018)
    The first measurements of anisotropic flow coefficients v(n) for mid-rapidity charged particles in Xe-Xe collisions at root s(NN)=5.44TeV are presented. Comparing these measurements to those from Pb-Pb collisions at root s(NN)=5.02 TeV, v(2) is found to be suppressed for mid-central collisions at the same centrality, and enhanced for central collisions. The values of v(3) are generally larger in Xe-Xe than in Pb-Pb at a given centrality. These observations are consistent with expectations from hydrodynamic predictions. When both v(2) and v(3) are divided by their corresponding eccentricities for a variety of initial state models, they generally scale with transverse density when comparing Xe-Xe and Pb-Pb, with some deviations observed in central Xe-Xe and Pb-Pb collisions. These results assist in placing strong constraints on both the initial state geometry and medium response for relativistic heavy-ion collisions. (c) 2018 European Organization for Nuclear Research. Published by Elsevier B.V.
  • The ALICE collaboration; Acharya, S.; Adamova, D.; Kim, D. J.; Krizek, F.; Molander, Mikael Andreas; Novitzky, Norbert; Onnerstad, A.; Parkkila, J. E.; Rytkönen, Heidi Maria; Räsänen, Sami; Saarimäki, Oskari Antti Matti; Slupecki, M.; Trzaska, W. H. (2021)
    Measurements of elliptic (v(2)) and triangular (v(3)) flow coefficients of pi(+/-), K-+/-, p+(p) over bar, K-S(0), and Lambda+(Lambda) over bar obtained with the scalar product method in Xe-Xe collisions at root sNN = 5.44TeV are presented. The results are obtained in the rapidity range |y| < 0.5 and reported as a function of transverse momentum, p(T), for several collision centrality classes. The flow coefficients exhibit a particle mass dependence for pT < 3 GeV/c, while a grouping according to particle type (i.e., meson and baryon) is found at intermediate transverse momenta (3 < p(T) < 8 GeV/c). The magnitude of the baryon v(2) is larger than that of mesons up to pT = 6 GeV/c. The centrality dependence of the shape evolution of the p(T)-differential v(2) is studied for the various hadron species. The v(2) coefficients of pi(+/-), K-+/-, and p+(p) over bar are reproduced by MUSIC hydrodynamic calculations coupled to a hadronic cascade model (UrQMD) for p(T) < 1 GeV/c. A comparison with vn measurements in the corresponding centrality intervals in Pb-Pb collisions at root sNN = 5.02TeV yields an enhanced v(2) in central collisions and diminished value in semicentral collisions.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2018)
    The elliptic (v(2)), triangular (v(3)), and quadrangular (v(4)) flow coefficients of pi(+/-), K-+/-, p + (p) over bar, Lambda + (Lambda) over bar, K-S(0)), and the phi-meson are measured in Pb-Pb collisions at root(NN)-N-s = 5.02 TeV. Results obtained with the scalar product method are reported for the rapidity range vertical bar y vertical bar < 0.5 as a function of transverse momentum, P-T, at different collision centrality intervals between 0-70%, including ultra-central (0-1%) collisions for pi(+/-), K-+/-, and p + (p) over bar. For P-T < 3 GeV/c, the flow coefficients exhibit a particle mass dependence. At intermediate transverse momenta (3 < p(T) < 8-10 GeV/c), particles show an approximate grouping according to their type (i.e., mesons and baryons). The phi-meson v(2), which tests both particle mass dependence and type scaling, follows p + <(p)over bar> v(2) at low P-T and pi(+/-) v(2) at intermediate p(T). The evolution of the shape of v(n) (p(T)) as a function of centrality and harmonic number n is studied for the various particle species. Flow coefficients of pi(+/-), K-+/- , and p + (p) over bar for p(T) < 3 GeV/c are compared to iEBE-VISHNU and MUSIC hydrodynamical calculations coupled to a hadronic cascade model (UrQMD). The iEBE-VISHNU calculations describe the results fairly well for P-T < 2.5 GeV/c, while MUSIC calculations reproduce the measurements for p(T) < 1 GeV/c. A comparison to vn coefficients measured in Pb-Pb collisions at root(NN)-N-s = 2.76 TeV is also provided.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Pekkanen, J.; Voutilainen, M.; Härkönen, J.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Tuominiemi, J.; Tuovinen, E.; Wendland, L.; Talvitie, J.; Tuuva, T. (2018)
    The Fourier coefficients v(2) and v(3) characterizing the anisotropy of the azimuthal distribution of charged particles produced in PbPb collisions at root S-NN = 5.02 TeV are measured with data collected by the CMS experiment. The measurements cover a broad transverse momentum range, 1 <p(T) <100 GeV/c. The analysis focuses on the p(T) > 10 GeV/c range, where anisotropic azimuthal distributions should reflect the path-length dependence of parton energy loss in the created medium. Results are presented in several bins of PbPb collision centrality, spanning the 60% most central events. The v(2) coefficient is measured with the scalar product and the multiparticle cumulant methods, which have different sensitivities to initial-state fluctuations. The values from both methods remain positive up to p(T) similar to 60-80 GeV/c, in all examined centrality classes. The v(3) coefficient, only measured with the scalar product method, tends to zero for p(T) greater than or similar to 20 GeV/c. Comparisons between theoretical calculations and data provide new constraints on the path-length dependence of parton energy loss in heavy ion collisions and highlight the importance of the initial-state fluctuations. (C) 2017 The Author. Published by Elsevier B.V.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2018)
    Measurements of anisotropic flow coefficients with two-and multi-particle cumulants for inclusive charged particles in Pb{Pb collisions at root s(NN) = 5 : 02 and 2.76TeV are reported in the pseudorapidity range vertical bar eta vertical bar <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) mu b(-1) in the centrality range 0{80%, is analysed. Flow coefficients up to the sixth flow harmonic (v6) are reported and a detailed comparison among results at the two energies is carried out. The pT 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)) similar to p(T)(n/3) 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(m)(n/m) are observed to be essentially independent of pT for most centralities up to about pT = 10 GeV/c. Analysing the di ff erences among higher-order cumulants of elliptic flow (v(2)), which have di ff erent 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 fi ts to cumulants. The measurements are compared to di ff erent model predictions in order to discriminate among initial-state models and to constrain the temperature dependence of the shear viscosity to entropy-density ratio.
  • Niemi, H.; Eskola, K. J.; Paatelainen, R. (2016)
    We introduce an event-by-event perturbative-QCD + saturation + hydro ("EKRT") framework for ultrarelativistic heavy-ion collisions, where we compute the produced fluctuating QCD-matter energy densities from next-to-leading-order perturbative QCD using a saturation conjecture to control soft-particle production and describe the space-time evolution of the QCD matter with dissipative fluid dynamics, event by event. We perform a simultaneous comparison of the centrality dependence of hadronic multiplicities, transverse momentum spectra, and flow coefficients of the azimuth-angle asymmetries against the LHC and RHIC measurements. We compare also the computed event-by-event probability distributions of relative fluctuations of elliptic flow and event-plane angle correlations with the experimental data from Pb + Pb collisions at the LHC. We show how such a systematic multienergy and multiobservable analysis tests the initial-state calculation and the applicability region of hydrodynamics and, in particular, how it constrains the temperature dependence of the shear viscosity-to-entropy ratio of QCD matter in its different phases in a remarkably consistent manner.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Pekkanen, J.; Voutilainen, M.; Härkönen, J.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Tuominen, E.; Tuominiemi, J.; Tuovinen, E.; Talvitie, J.; Tuuva, T. (2018)
    The prompt D-0 meson azimuthal anisotropy coefficients, v(2) and ?v(3), are measured at midrapidity ( |y| < 1.0) in Pb-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum (p(T)) range of 1 to 40 GeV/c, for central and midcentral collisions. The v(2) coefficient is found to be positive throughout the p(T) range studied. The first measurement of the prompt D-0 meson v(3) coefficient is performed, and values up to 0.07 are observed for p(T) around 4 GeV/c. Compared to measurements of charged particles, a similar p(T) dependence, but smaller magnitude for p(T) < 6 GeV/r, is found for prompt D-0 meson v(2) and v(3) coefficients. The results are consistent with the presence of collective motion of charm quarks at low p(r) and a path length dependence of charm quark energy loss at high p(r), thereby providing new constraints on the theoretical description of the interactions between charm quarks and the quark-gluon plasma.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Chang, B.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2018)
    The correlations between event-by-event fluctuations of anisotropic flow harmonic amplitudes have been measured in Pb-Pb collisions at root s(NN) = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The results are reported in terms of multiparticle correlation observables dubbed symmetric cumulants. These observables are robust against biases originating from nonflow effects. The centrality dependence of correlations between the higher order harmonics (the quadrangular v(4) and pentagonal v(5) flow) and the lower order harmonics (the elliptic v(2) and triangular v(3) flow) is presented. The transverse momentum dependences of correlations between v(3) and v(2) and between v(4) and v(2) are also reported. The results are compared to calculations from viscous hydrodynamics and a multiphase transport (AMPT) model calculations. The comparisons to viscous hydrodynamic models demonstrate that the different order harmonic correlations respond differently to the initial conditions and the temperature dependence of the ratio of shear viscosity to entropy density (eta/s). Asmall average value of eta/s is favored independent of the specific choice of initial conditions in the models. The calculations with the AMPT initial conditions yield results closest to the measurements. Correlations among the magnitudes of v(2), v(3), and v(4) show moderate p(T) dependence in midcentral collisions. This might be an indication of possible viscous corrections to the equilibrium distribution at hadronic freeze-out, which might help to understand the possible contribution of bulk viscosity in the hadronic phase of the system. Together with existing measurements of individual flow harmonics, the presented results provide further constraints on the initial conditions and the transport properties of the system produced in heavy-ion collisions.