123 research outputs found

    Do nuclear collisions create a locally equilibrated quark-gluon plasma?

    Full text link
    Experimental results on azimuthal correlations in high energy nuclear collisions (nucleus-nucleus, proton-nucleus and proton-proton) seem to be well described by viscous hydrodynamics. It is often argued that this agreement implies either local thermal equilibrium or at least local isotropy. In this note, I present arguments why this is not the case. Neither local near-equilibrium nor near-isotropy are required in order for hydrodynamics to offer a successful and accurate description of experimental results. However, I predict the breakdown of hydrodynamics at momenta of order seven times the temperature, corresponding to a smallest possible QCD liquid drop size of 0.15 fm.Comment: 14 pages, 6 figures; v2: references added, major changes in section VI, qualitative conclusions unchanged; v3: minor typos fixed, matches published versio

    Cold deconfined matter EOS through an HTL quasi-particle model

    Full text link
    Using quasi-particle models, lattice data can be mapped to finite chemical potential. By comparing a simple and an HTL quasi-particle model, we derive the general trend that a full inclusion of the plasmon effect will give.Comment: 5 pages, 6 figures, contribution to the conference Strong and Electroweak Matter (SEWM2002), Heidelberg, Germany, October 2-5, 2002; v2: plots and references update

    Relativistic Hydrodynamic Attractors with Broken Symmetries: Non-Conformal and Non-Homogeneous

    Full text link
    Standard textbooks will state that hydrodynamics requires near-equilibrium to be applicable. Recently, however, out-of-equilibrium attractor solutions for hydrodynamics have been found in kinetic theory and holography in systems with a high degree of symmetry, suggesting the possibility of a genuine out-of-equilibrium formulation of hydrodynamics. This work demonstrates that attractor solutions also occur in non-conformal kinetic theory and spatially non-homogeneous systems, potentially having important implications for the interpretation of experimental data in heavy-ion and proton-proton collisions and relativistic fluid dynamics as a whole.Comment: 13 pages, 2 figures; v2: minor changes (typos, etc.); v3: matches published versio

    Azimuthal Anisotropies at High Momentum from Purely Non-Hydrodynamic Transport

    Full text link
    In the limit of short mean free path, relativistic kinetic theory gives rise to hydrodynamics through a systematically improvable gradient expansion. In the present work, a systematically improvable expansion in the opposite limit of large mean free path is considered, describing the dynamics of particles which are almost, but not quite, non-interacting. This non-hydrodynamic "eremitic" expansion does not break down for large gradients, and may be useful in situations where a hydrodynamic treatment is not applicable. As applications, azimuthal anisotropies at high transverse momentum in Pb+Pb and p+Pb collisions at s=5.02\sqrt{s}=5.02 TeV are calculated from the first order eremitic expansion of kinetic theory in the relaxation time approximation.Comment: 26 pages, 5 figures; v2: reference to Borghini and Gombeaud added who discussed same setup in 2010, typos corrected; v3: minor changes, matches published versio

    Light-Heavy Ion Collisions: A window into pre-equilibrium QCD dynamics?

    Full text link
    Relativistic collisions of light on heavy ions (p+Au at sqrt(s)=7.7 GeV, p+Au, d+Au,3He+Au at sqrt(s)=62.4 GeV and 200 GeV and p+Pb, 3He+Pb at sqrt(s)=5.02 TeV) are simulated using "superSONIC", a model that includes pre-equilibrium flow, viscous hydrodynamics and a hadronic cascade afterburner. Even though these systems have strong gradients and only consist of at most a few tens of charged particles per unit rapidity, one finds evidence that a hydrodynamic description applies to these systems. Based on these simulations, the presence of a triangular flow component in d+Au collisions at sqrt(s)=200 GeV is predicted to be similar in magnitude to that found in 3He+Au collisions. Furthermore, the v3(p_T) ratio of 3He+Au to d+Au is found to be sensitive to the presence of pre-equilibrium flow. This would imply an experimentally accessible window into pre-equilibrium QCD dynamics using light-heavy ion collisions.Comment: 8 pages plus appendix; 9 figure

    Collective flow without hydrodynamics: simulation results for relativistic ion collisions

    Get PDF
    Flow signatures in experimental data from relativistic ion collisions are usually interpreted as a fingerprint of the presence of a hydrodynamic phase during the evolution of these systems. In this work, flow signatures arising from event-by-event viscous hydrodynamics are compared to those arising from event-by-event non-interacting particle dynamics (free-streaming), both followed by a late-stage hadronic cascade, in d+Au, 3He+Au at sqrt(s)=200 GeV and p+Pb collisions at sqrt(s)=5 TeV, respectively. For comparison, also Pb+Pb collisions at sqrt(s)=2.76 TeV are simulated. It is found that non-hydrodynamic evolution can give rise to equal or larger radial flow than hydrodynamics with eta/s=0.08 in all simulated collision systems. In light-on-heavy-ion collisions, free-streaming gives rise to triangular and quadrupolar flow comparable to or larger than that from hydrodynamics, but it generally leads to considerably smaller elliptic flow. As expected, free-streaming leads to considerably less elliptic, triangular and quadrupolar flow than hydrodynamics in nucleus-nucleus collisions, such as event-by-event Pb+Pb collisions at sqrt(s)=2.76 TeV.Comment: 18 pages; 9 figures; v2: minor errors corrected, HBT radii added; v3: added subsection on radial flow breakdown in peripheral p+Pb, matches published versio
    • …
    corecore