311 research outputs found

    Interference Phenomena in Medium Induced Radiation

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    We consider the interference pattern for the medium-induced gluon radiation produced by a color singlet quark-antiquark antenna embedded in a QCD medium with size LL and `jet quenching' parameter q^\hat q. Within the BDMPS-Z regime, we demonstrate that, for a dipole opening angle θqqˉθc2/q^L3\theta_{q\bar q} \gg\theta_c\equiv {2}/{\sqrt{\hat q L^3}}, the interference between the medium--induced gluon emissions by the quark and the antiquark is suppressed with respect to the direct emissions. This is so since direct emissions are delocalized throughout the medium and thus yield contributions proportional to LL while interference occurs only between emissions at early times, when both sources remain coherent. Thus, for \tqq \gg\theta_c, the medium-induced radiation is the sum of the two spectra individually produced by the quark and the antiquark, without coherence effects like angular ordering. For \tqq \ll\theta_c, the medium--induced radiation vanishes.Comment: 4 pages, 2 figures; Proceedings of the "Quark Matter 2011" conferenc

    Angular Dependence of Jet Quenching Indicates Its Strong Enhancement Near the QCD Phase Transition

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    We study dependence of jet quenching on matter density, using "tomography" of the fireball provided by RHIC data on azimuthal anisotropy v2v_2 of high ptp_t hadron yield at different centralities. Slicing the fireball into shells with constant (entropy) density, we derive a "layer-wise geometrical limit" v2maxv_2^{max} which is indeed above the data v2<v2maxv_2<v_2^{max}. Interestingly, the limit is reached only if quenching is dominated by shells with the entropy density exactly in the near-TcT_c region. We show two models that simultaneously describe the high ptp_t v2v_2 and RAAR_{AA} data and conclude that such a description can be achieved only if the jet quenching is few times stronger in the near-TcT_c region relative to QGP at T>TcT>T_c. One possible reason for that may be recent indications that the near-TcT_c region is a magnetic plasma of relatively light color-magnetic monopoles.Comment: 4 pages, 4 figures. Final version published as PRL102,202302(2009

    Jet quenching via jet collimation

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    The strong modifications of dijet properties in heavy ion collisions measured by ATLAS and CMS provide important constraints on the dynamical mechanisms underlying jet quenching. In this work, we show that the transport of soft gluons away from the jet cone - jet collimation - can account for the observed dijet asymmetry with values of q^L\hat{q}\, L that lie in the expected order of magnitude. Further, we show that the energy loss attained through this mechanism results in a very mild distortion of the azimuthal angle dijet distribution.Comment: 4 pages, 2 figures; Proceedings of the "Quark Matter 2011" conferenc

    Correlations of Electrons from Heavy Flavor Decay with Hadrons in Au+Au and p+p Collisions

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    Measurements of electrons from the decay of open-heavy flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled p+p collisions. These measurements indicate that charm and bottom quarks interact with the hot-dense matter produced in heavy-ion collisions much more than expected. Here we extend these studies to two-particle correlations where one particle is an electron from the decay of a heavy-flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interactions between heavy quarks and the matter, such as whether the modifcation of the away-side-jet shape seen in hadron-hadron correlations is present when the trigger particle is from heavy-meson decay and whether the overall level of away-side-jet suppression is consistent. We statistically subtract correlations of electrons arising from background sources from the inclusive electron-hadron correlations and obtain two-particle azimuthal correlations at sNN\sqrt{s_{NN}} =200 GeV between electrons from heavy-flavor decay with charged hadrons in p+p and also first results in Au+Au collisions. We find the away-side-jet shape and yield to be modified in Au+Au collisions compared to p+p collisions.Comment: talk given at Winter Workshop in Nuclear Dynamics 201

    Heavy-quark energy loss and thermalization in a strongly coupled SYM plasma

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    Using the AdS/CFT correspondence, we compute the radiative energy loss of a slowly decelerating heavy quark with mass M moving through a supersymmetric Yang Mills (SYM) plasma at temperature T at large t'Hooft coupling \lambda. The calculation is carried out in terms of perturbation in \sqrt{\lambda}T/M, and the rate of the energy loss is computed up to second order. We explain the physical meaning of each correction and estimate the thermalization time of a heavy quark moving in a strongly-coupled plasma.Comment: 14 pages, 1 figur