Search

Abstract: We obtain the radiative energy loss of a heavy quark in a deconfined medium due to radiation of gluons off them using a recently derived generalised gluon emission spectrum. We find that the heavy flavour loses energy almost in a similar fashion like light quarks through this process. With this, we further analyse the nuclear modification factor for D-meson at LHC and RHIC energies. In particular, the obtained result is found to be in close agreement with the most recent data from ALICE collaboration at 2.76 ATeV Pb–Pb collisions. We also discuss the nuclear modification factor due to the collisional energy loss. Furthermore, the result of non-photonic single electron from the decay of both D- and B-mesons is compared with the RHIC data at 200 AGeV Au–Au collisions, which is also in close agreement. [Copyright &y& Elsevier]

Photon-pair direct or jet-associated production is important for relevant standard model measurement, Higgs and new physics searches at the Large Hadron Collider (LHC). The loop-induced gluon-fusion process gg → &ggr;&ggr;g, which formally contributes only at the next-to-next-to-leading order to &ggr;&ggr; j productions, may get enhanced by the large gluon flux at the LHC. We have checked and confirmed previous results on gg→ &ggr;&ggr; (Dicus and Willenbrock 1988 Phys. Rev.D37 1801), &ggr;&ggr;g (de Florian and Kunszt 1999 Phys. Lett. B 460 184) at one loop, using the traditional Feynman diagram based approach, taking into account the quark mass effects, and updated them further for the 7 and 14 TeV LHC with new inputs and settings. We provide the details and results of the calculations, which involve manipulation of rank-5 pentagon integrals. Our results show that the gluon-fusion process can contribute about 10% of the Born result, especially at small M&ggr;&ggr; and PT &ggr;&ggr;, and increase further the overall scale uncertainty. Top quark loop effects are examined in detail, which become important near or above the threshold M&ggr;&ggr; ≳ 2mt . [ABSTRACT FROM AUTHOR]

We present our results on the shear viscosity to entropy ratio ( η/ s) in the framework of the clustering of the color sources of the matter produced at RHIC and LHC energies. The onset of de-confinement transition is identified by the spanning percolating cluster in 2D percolation. The relativistic kinetic theory relation for η/ s is evaluated using the initial temperature ( T) and the mean free path ( λ). The analytic expression for η/ s covers a wide temperature range. At T∼150 MeV below the hadron to QGP transition temperature of ∼168 MeV, with increasing temperatures the η/ s value drop sharply and reaches a broad minimum η/ s∼0.20 at T∼175-185 MeV. Above this temperature η/ s grows slowly. The measured values of η/ s are 0.204±0.020 and 0.262±0.026 at the initial temperature of 193.6±3 MeV from central Au+Au collisions at $\sqrt{s_{NN}}=200~\mathrm{GeV}$ (RHIC) and 262.2±13 MeV in central Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76~\mathrm{TeV}$ (LHC). These η/ s values are 2.5 and 3.3 times the AdS/CFT conjectured lower bound 1/4 π but are consistent with theoretical η/ s estimates for a strongly coupled QGP. [ABSTRACT FROM AUTHOR]

Abstract: We show that if a flavour-less vector meson remains bound after deconfinement, and if its limiting velocity in the quark-gluon plasma is subluminal, then this meson produces a distinct peak in the spectrum of thermal photons emitted by the plasma. We also demonstrate that this effect is a universal property of all strongly coupled, large- plasmas with a gravity dual. For the the corresponding peak lies between 3 and 5 GeV and could be observed at the LHC. [Copyright &y& Elsevier]