Using combined data from the Relativistic Heavy Ion and Large Hadron Colliders, we constrain the shear and bulk viscosities of quark-gluon plasma (QGP) at temperatures of ∼ 150 – 350 MeV . We use ...Bayesian inference to translate experimental and theoretical uncertainties into probabilistic constraints for the viscosities. With Bayesian model averaging we propagate an estimate of the model uncertainty generated by the transition from hydrodynamics to hadron transport in the plasma's final evolution stage, providing the most reliable phenomenological constraints to date on the QGP viscosities.
Ultra-peripheral heavy ion collisions provide a unique opportunity to study the parton distributions in the colliding nuclei via the measurement of photo-nuclear jet production. An analysis of jet ...production in ultra-peripheral Pb+Pb collisions at sNN=5.02 TeV performed using data collected with the ATLAS detector in 2015 is described. The data set corresponds to a total Pb+Pb integrated luminosity of 0.38 nb−1. The ultra-peripheral collisions are selected using a combination of forward neutron and rapidity gap requirements. The cross-sections, not unfolded for detector response, are compared to results from Pythia Monte Carlo simulations re-weighted to match a photon spectrum obtained from the STARlight model. Qualitative agreement between data and these simulations is observed over a broad kinematic range suggesting that using these collisions to measure nuclear parton distributions is experimentally realisable.
Measurements of jet suppression in Pb + Pb collisions by the ATLAS Collaboration are reported. The production of inclusive jet yields as a function of jet pT, collision centrality and jet size ...parameter R are measured and presented through the central-to-peripheral ratio, RCP. Jets are found to be suppressed in central collisions relative to peripheral collisions by approximately a factor of two. The suppression is found to show almost no variation with jet pT, and the RCP is found to increase slighly with increasing R. Measurements of heavy quark energy loss are also presented using muons from semi-leptonic decays of heavy flavor hadrons. The maximal suppression is observed to be RCP∼0.5 and shows no significant depedence on the muon pT.
Measurements of inclusive jet suppression in Pb + Pb collions at sNN=2.76 TeV with the ATLAS detector are reported. The centrality, pT and jet size dependence of the central-to-peripheral ratio, RCP, ...is presented. The results indicate that jets are suppressed by approximately a factor of two in the most central collisions, and a significant dependence on the jet size is observed. The path length dependence of jet quenching is studied through measurements of inclusive jet suppression as a function of angle with respect to the event plane. The azimuthal modulation of the jet yield is quantified by its second Fourier coefficent, ν2, which is significant in all pT and centrality ranges presented.
We present a new study of jet interactions in the quark-gluon plasma created in high-energy heavy-ion collisions, using a multistage event generator within the jetscape framework. We focus on ...medium-induced modifications in the rate of inclusive jets and high transverse momentum (high-pT) hadrons. Scattering-induced jet energy loss is calculated in two stages: a high virtuality stage based on the matter model, in which scattering of highly virtual partons modifies the vacuum radiation pattern, and a second stage at lower jet virtuality based on the lbt model, in which leading partons gain and lose virtuality by scattering and radiation. Coherence effects that reduce the medium-induced emission rate in the matter phase are also included. The trento model is used for initial conditions, and the (2 + 1)dimensional vishnu model is used for viscous hydrodynamic evolution. Jet interactions with the medium are modeled via 2-to-2 scattering with Debye screened potentials, in which the recoiling partons are tracked, hadronized, and included in the jet clustering. Holes left in the medium are also tracked and subtracted to conserve transverse momentum. Calculations of the nuclear modification factor (RAA) for inclusive jets and high-pT hadrons are compared to experimental measurements at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). Within this framework, we find that with one extra parameter which codifies the transition between stages of jet modification—along with the typical parameters such as the coupling in the medium, the start and stop criteria, etc.—we can describe these data at all energies for central and semicentral collisions without a rescaling of the jet transport coefficient qˆ.
Parton energy-momentum exchange with the quark gluon plasma (QGP) is a multiscale problem. In this work, we calculate the interaction of charm quarks with the QGP within the higher twist formalism at ...high virtuality and high energy using the Modular All Twist Transverse-scattering Elastic-drag and Radiation (MATTER) model, while the low-virtuality and high-energy portion is treated via a linearized Boltzmann transport formalism. Coherence effect that reduces the medium-induced emission rate in the MATTER model is also taken into account through a virtuality-dependent qˆ, leaving the simultaneous dependence of qˆ on heavy quark mass and virtuality for future studies. The interplay between these two formalisms is studied phenomenologically and used to produce a first description of the D-meson and charged hadron nuclear modification factor RAA across multiple centralities. As a result, all calculations were carried out utilizing the Jet Energy-loss Tomography with a Statistically and Computationally Advanced Program Envelope framework.
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