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The transport coefficient $hat{q}$ in an anisotropic plasma

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 Added by Yacine Mehtar-Tani
 Publication date 2009
  fields
and research's language is English




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We investigate the jet quenching parameter in the case of a fast moving quark in an anisotropic plasma. In the leading log approximation, strong indications are found that the transport coefficient increases with increasing anisotropy. Implications for the phenomenology at RHIC are discussed.



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We report the effect of magnetic field on estimation of jet transport coefficient, $hat{q}$ using a simplified quasi-particle model. Our adopted quasi-particle model introduces temperature and magnetic field dependent degeneracy factors of partons, which are tuned by fitting the magneto-thermodynamical data of lattice quantum chromodynamics. In absence of magnetic field, $hat{q}$ is estimated by using the temperature dependent degeneracy factor. At finite magnetic field, ${hat q}$ splits into parallel and perpendicular components, whose magnetic field dependent part has two sources. One is field dependent degeneracy factor and another is phase space part, guided from shear viscosity to entropy density ratio. Their collective role provides an enhanced jet transport coefficients, which should be considered in detailed jet quenching phenomenology in presence of magnetic field.
We present a new determination of $hat{q}$, the jet transport coefficient of the quark-gluon plasma. Using the JETSCAPE framework, we use Bayesian parameter estimation to constrain the dependence of $hat{q}$ on the jet energy, virtuality, and medium temperature from experimental measurements of inclusive hadron suppression in Au-Au collisions at RHIC and Pb-Pb collisions at the LHC. These results are based on a multi-stage theoretical approach to in-medium jet evolution with the MATTER and LBT jet quenching models. The functional dependence of $hat{q}$ on jet energy, virtuality, and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of MATTER and LBT. The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. These results provide state-of-the-art constraints on $hat{q}$ and lay the groundwork to extract additional properties of the quark-gluon plasma from jet measurements in heavy-ion collisions.
Within a multi-phase transport model with string melting scenario, jet transport parameter $hat{q}$ is calculated in Au+Au collisions at $sqrt{s_{NN} } $= 200 GeV and Pb+Pb collisions at $sqrt{s_{NN} } $= 2.76 TeV. The $hat{q}$ increases with the increasing of jet energy for both partonic phase and hadronic phase. The energy and path length dependences of $hat{q}$ in full heavy-ion evolution are consistent with the expectations of jet quenching. The correlation between jet transport parameter $hat{q}$ and dijet transverse momentum asymmetry $A_{J}$ is mainly investigated, which discloses that a larger $hat{q}$ corresponds to a larger $A_{J}$. It supports a consistent jet energy loss picture from the two viewpoints of single jet and dijet. It is proposed to measure dijet asymmetry distributions with different jet transport parameter ranges as a new potential method to study jet quenching physics in high energy heavy-ion collisions.
We determine the hard-loop resummed propagator in an anisotropic QCD plasma in general covariant gauges and define a potential between heavy quarks from the Fourier transform of its static limit. We find that there is stronger attraction on distance scales on the order of the inverse Debye mass for quark pairs aligned along the direction of anisotropy than for transverse alignment.
104 - S. Cao , Y. Chen , J. Coleman 2021
We report a new determination of $hat{q}$, the jet transport coefficient of the Quark-Gluon Plasma. We use the JETSCAPE framework, which incorporates a novel multi-stage theoretical approach to in-medium jet evolution and Bayesian inference for parameter extraction. The calculations, based on the MATTER and LBT jet quenching models, are compared to experimental measurements of inclusive hadron suppression in Au+Au collisions at RHIC and Pb+Pb collisions at the LHC. The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. The functional dependence of $hat{q}$ on jet energy or virtuality and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of MATTER and LBT. In the multi-stage approach, the switch between MATTER and LBT is governed by a virtuality scale $Q_0$. Comparison of the posterior model predictions to the RHIC and LHC hadron suppression data shows reasonable agreement, with moderate tension in limited regions of phase space. The distribution of $hat{q}/T^3$ extracted from the posterior distributions exhibits weak dependence on jet momentum and medium temperature $T$, with 90% Credible Region (CR) depending on the specific choice of model configuration. The choice of MATTER+LBT, with switching at virtuality $Q_0$, has 90% CR of $2<hat{q}/T^3<4$ for $p_mathrm{T}^mathrm{jet}>40$ GeV/c. The value of $Q_0$, determined here for the first time, is in the range 2.0-2.7 GeV.
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