5 pages, 2 figures, Proceedings of the IIIrd Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions (HotQuarks08), Estes Park, USA, August 18-23 2008
We consider heavy-quark energy loss and pT-broadening in a strongly-coupled N=4 Super Yang Mills (SYM) plasma, and the problem of finite-extend matter is addressed. When expressed in terms of the appropriate saturation momentum, one finds identical parametric forms for the energy loss in pQCD and SYM theory, while pT-broadening is radiation dominated in SYM theory and multiple scattering dominated in pQCD.
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" approximati…
Recent surprising discoveries of collective behaviour of low-$p_T$ particles in $pA$ collisions at LHC hint at the creation of a hot, fluid-like QGP medium. The seemingly conflicting measurements of non-zero particle correlations and $R_{pA}$ that appears to be consistent with unity demand a more careful analysis of the mechanisms at work in such ostensibly minuscule systems. We study the way in which energy is dissipated in the QGP created in $pA$ collisions by calculating, in pQCD, the short separation distance corrections to the well-known DGLV energy loss formulae that have produced excell…
Heavy quarks (charm and bottoms) are one of the few probes which are sensitive to the degrees of freedom of a Quark Gluon Plasma (QGP), which cannot be revealed by lattice gauge calculations in equilibrium. Due to the rapid expansion of the QGP energetic heavy quarks do not come to an equilibrium with the QGP. Their energy loss during the propagation through the QGP medium depends strongly on the modelling of the interaction of the heavy quarks with the QGP quarks and gluons, i.e. on the assuption of the degrees of freedom of the plasma. Here we compare the results of different models, the pQC…
Dilepton production by dynamical quasiparticles in the strongly interacting quark gluon plasma
讨论了强相互作用夸克胶子等离子体（sQGP）组分产生双轻子的问题。为了在较低的等离子体温度（O（T_c））、较低的双轻子质量（O（1GeV））和较强的耦合（α S =0.5-1）下进行定量预测，我们不仅考虑了高阶pQCD反应机制，而且考虑了夸克、反夸克和胶子的非微扰谱函数（离壳）和自能，从而超出了主导扭转。为此，我们的计算利用了匹配的动力学准粒子模型（DQPM）提供的夸克和胶子非微扰传播子的参数化来重现晶格数据。DQPM用单粒子格林函数描述QCD性质（在两粒子不可约方法的意义上），并导致sQGP的成分是有效准粒子的概念，这些准粒子是大质量的，具有宽谱函数（由于大的相互作用速率）。本文导出了反应q+qbar->l^+l^-中双轻子产生的离壳层截面。（Drell-Yan机理），q+qbar->g+l^+l^-（夸克湮灭与末态的胶子韧致辐射），q（qbar）+g->q（qbar）+l^+l^-通过用夸克和胶子的DQPM传播子修饰微扰图中的夸克和胶子线，得到了sQGP中g->q+qbar+l ^+l^-和q（qbar）->q（qbar）+g+l^+l^-（虚胶子衰变，虚夸克衰变）的关系.
The drag and diffusion coefficients of heavy quarks propagating through quark gluon plasma (QGP) have been estimated by shielding both the electric and magnetic type infra-red divergences. The electric type screening in perturbative quantum chromodynamics (pQCD) has been widely studied and used in evaluating the diffusion coefficient of heavy quarks (HQs). To our knowledge the impact of magnetic screening in diffusion coefficients of HQs is not studied before. It is found that the effect of magnetic screening mass on the drag and diffusion coefficients of HQs is quite significant and its contr…
Heavy-flavour quarks are predominantly produced in hard scatterings on a short time-scale and traverse the medium interacting with its constituents, thus they are one of the effective probes of the transport properties of the medium formed in relativistic heavy ion collisions. On the other hand, the thermal production of heavy-flavour quarks in quark-gluon plasma (QGP) is itself of interest. In this report, the production and elliptic flow of the prompt charmed mesons $D^0$, $D^+$, $D^{*+}$ and $J/ψ$ in PbPb collisions at the center-of-mass energy 2.76 TeV per nucleon pair are described in the…
We compute O(g) NLO corrections to the transverse scattering kernel and transverse momentum broadening coefficient $\hat{q}$ of weakly-coupled $\mathcal{N}=4$ SYM. Based on this, we also compute NLO correction to the collinear splitting rates. For $\hat{q}$ we find that the NLO/LO ratio is similar to the QCD one, with large NLO corrections. This is contrasted by our findings for the collinear splitting rate, which show a much better convergence in SYM than in QCD, providing further support to earlier expectations that NLO corrections have signs and relative magnitudes controlled by the specifi…
We study momentum imbalance as a function of jet asymmetry in high-energy heavy-ion collisions. To implement parton production during the collision, we include all Leading Order (LO) $2\to 2$ and $2\to 3$ parton processes in pQCD. The produced partons lose energy within the quark gluon plasma and hadronize collinearly when they leave it. The energy and momentum deposited into the plasma is described using linear viscous hydrodynamics with a constant energy loss per unit length and a total energy loss given by a Gaussian probability centered around a mean value $\bar{\mathcal{E}}$ and a half-wi…
Jet energy loss and single inclusive jet suppression in high-energy heavy-ion collisions are studied within a pQCD parton model that includes both elastic and radiative interactions between jet shower and medium partons as they propagate through the quark-gluon plasma. The collisional energy loss of jets with a given cone-size is found to be relatively small comparing with the radiative energy loss. However the effect of transverse momentum broadening due to elastic scattering is significant in the calculation of radiative energy loss within the higher-twist formalism. The nuclear modification…
The scaling property of large-$p_\perp$ hadron suppression, $R_{\rm{AA}}(p_\perp)$, measured in heavy ion collisions at RHIC and LHC leads to the determination of the average parton energy loss $\langle ε\rangle$ in quark-gluon plasma produced in a variety of collision systems and centrality classes. Relating $\langle ε\rangle$ to the particle multiplicity and collision geometry allows for probing the dependence of parton energy loss on the path-length $L$. We find that $\langle ε\rangle \propto L^β$ with $β=1.02^{+0.09}_{-0.06}$, consistent with the pQCD expectation of parton energy loss in a…
