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Nuclear Theory·nucl-th

Friday·December 14, 2018

8 papers—4 primary·4 cross-listed

All8Primary4Cross-lists4
  1. 05

    Sorting out quenched jets

    Jasmine Brewer🇺🇸 · José Guilherme Milhano🇵🇹 · Jesse Thaler🇺🇸

    We introduce a new 'quantile' analysis strategy to study the modification of jets as they traverse through a droplet of quark-gluon plasma. To date, most jet modification studies have been based on comparing the jet properties measured in heavy-ion collisions to a proton-proton baseline at the same reconstructed jet transverse momentum (). It is well known, however, that the quenching of jets from their interaction with the medium leads to a migration of jets from higher to lower , making it challenging to directly infer the degree and mechanism of jet energy loss. Our proposed quantile matching procedure is inspired by (but not reliant on) the approximate monotonicity of energy loss in the jet . In this strategy, jets in heavy-ion collisions ordered by are viewed as modified versions of the same number of highest-energy jets in proton-proton collisions, and the fractional energy loss as a function of jet is a natural observable (). Furthermore, despite non-monotonic fluctuations in the energy loss, we use an event generator to validate the strong correlation between the of the parton that initiates a heavy-ion jet and the of the vacuum jet which corresponds to it via the quantile procedure (). We demonstrate that this strategy both provides a complementary way to study jet modification and mitigates the effect of migration in heavy-ion collisions.

    ↳ hep-phhep-exnucl-exnucl-thPRL(2019)·50 citations
  2. 06

    Stochastic hydrodynamics and long time tails of an expanding conformal charged fluid

    M. Martinez🇺🇸 · Thomas Schaefer🇺🇸

    We investigate the impact of hydrodynamic fluctuations on correlation functions in a scale invariant fluid with a conserved charge. The kinetic equations for the two-point functions of pressure, momentum and heat energy densities are derived within the framework of stochastic hydrodynamics. The leading non-analytic contributions to the energy-momentum tensor as well as the current are determined from the solutions to these kinetic equations. In the case of a static homogeneous background we show that the long time tails obtained from hydro-kinetic equations reproduce the one-loop results derived from statistical field theory. We use these results to establish bounds on transport coefficients. We generalize the stochastic equation to a background flow undergoing Bjorken expansion. We compute the leading fractional power correction to the current and compare with the first order gradient term.

    ↳ hep-thcond-mat.stat-mechhep-phnucl-thPRC(2019)·56 citations
  3. 07

    A new pQCD based Monte Carlo event generator for jets in the quark-gluon plasma

    Paul Caucal🇫🇷 · Edmond Iancu🇫🇷 · Alfred H. Mueller🇺🇸 · Gregory Soyez🇫🇷

    A main difficulty in understanding the dynamics of jets produced in the high-density environment of ultrarelativistic heavy ion collision, is to provide a unified description for the two sources of radiation that are a priori expected: the "vacuum-like" emissions responsible for the parton shower from large virtualities down to the hadronisation scale and the "medium-induced" emissions responsible for the energy loss by the jet. In the recent paper arXiv:1801.09703, we demonstrated that these two mechanisms can be factorized from each other within a controlled, "double-logarithmic" approximation in perturbative QCD. In this proceeding we recall the main features of the jet evolution in a dense QCD medium. We emphasize that the in-medium parton showers differ from those in the vacuum in two crucial aspects: their phase-space is reduced and the first emission outside the medium can violate angular ordering. Based on this factorized picture, which is Markovian, we have recently developed a Monte Carlo event generator which includes both vacuum-like and medium-induced emissions and goes beyond the double logarithmic approximation. We here present our first results for the fragmentation function and the energy loss by the jet.

    ↳ hep-phnucl-thPoS(2019)·12 citations
  4. 08

    Polarized baryon production in heavy ion collisions: an analytic hydrodynamical study

    Balint Boldizsar🇭🇺 · Marton I. Nagy🇭🇺 · Mate Csanad🇭🇺

    We utilize known exact analytic solutions of perfect fluid hydrodynamics to analytically calculate the polarization of baryons produced in heavy ion collisions. Assuming local thermodynamical equilibrium also for spin degrees of freedom, baryons get a net polarization at their formation (freeze-out). This polarization depends on the time evolution of the Quark-Gluon Plasma (QGP), which can be described as an almost perfect fluid. By using exact analytic solutions, we thus can analyze the necessity of rotation (and vorticity) for non-zero net polarization. In this paper we give the first analytical calculations for the polarization four-vector. We use two hydrodynamical solutions; one is the spherically symmetric Hubble flow (a somewhat oversimplified model, to demonstrate the methodology). The other solution which we use is a somewhat more involved one that corresponds to a rotating and accelerating expansion, and is thus well suited to investigate some main features of the time evolution of the QGP created in peripheral heavy-ion collisions (although there are still many numerous features of a real collision geometry that are beyond the reach of this simple model). Finally we illustrate and discuss our results on the polarization.

    ↳ hep-phnucl-thUniverse(2019)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE