Transverse energy distributions and J/ψJ/\psi production in Pb+Pb collisions

We have analyzed the latest NA50 data on transverse energy distributions and $J/\psi$ suppression in Pb+Pb collisions. The transverse energy distribution was analysed in the geometric model of AA collisions. In the geometric model, fluctuations in the number of NN collisions at fixed impact parameter are taken into account. Analysis suggests that in Pb+Pb collisions, individual NN collisions produces less $$, than in other AA collisions. The nucleons are more transparent in Pb+Pb collisions. The transverse energy dependence of the $J/\psi$ suppression was obtained following the model of Blaizot et al, where charmonium suppression is assumed to be 100% effective above a threshold density. With fluctuations in number of NN collisions taken into account, good fit to the data is obtained, with a single parameter, the threshold density.Comment: Revised version with better E_T fit. 4 pages, 2 figure

Novel features of J/ΨJ/\Psi dissociation in matter

We make a detailed study of the effect that the recently predicted modification of the in-medium masses of charmed mesons would have on $J/\Psi$ dissociation on pion and $\rho$-meson comovers in relativistic heavy ion collisions. We find a substantial dependence of the $J/\Psi$ absorption rates on the density and temperature of the nuclear matter. This suggests that a quantitative analysis of $J/\Psi$ dissociation in nucleus nucleus collisions should include the effects of the modification of meson masses in dense matter.Comment: 7 pages, espcrc2, including 5 ps-figures, to be pub. in Phys. Lett.

Screening and Anti-Screening Effects in J/psi Production on Nuclei

The nuclear effects in J/psi hadro- and electroproduction on nuclei are considered in framework of reggeon approach. It is shown that screening regime which holds for electroproduction at x_F > 0.7 and for hadroproduction at x_F > -(0.3-0.4) is changed with anti-screening regime for smaller x_F values.Comment: 6 pages, 6 figures. Small changes in wordin

Heavy Quarkonia Production in p+p Collisions from the PHENIX Experiment

Quarkonia provide a sensitive probe of the properties of the hot dense medium created in high energy heavy ion collisions. Hard scattering processes result in the production of heavy quark pairs that interact with the collision medium during hadronization. These in-medium interactions convey information about the fundamental properties of the medium itself and can be used to examine the modification of the QCD confining potential in the collision environment. Baseline measurements from p+p and d+Au collision systems are used to distinguish cold nuclear matter effects while measurements from heavy ion collision systems are used to quantify in-medium effects. The PHENIX experiment has the capability of detecting heavy quarkonia at $1.2<|\eta|<2.2$ via the $\mu^+\mu^-$ decay channel and at $|\eta|<0.35$ via the $e^+e^-$ decay channel. Recent runs have resulted in the collection of high statistics p+p data sets that provide an essential baseline reference for heavy ion measurements and allow for further critical evaluation of heavy quarkonia production mechanisms. The latest PHENIX results for the production of the $J/\psi$ in p+p collisions are presented and future prospects for $\psi'$, $\chi_{c}$ and $\Upsilon$ measurements are discussed.Comment: 4 pages, 2 figures, Proceedings for Quark Matter 200

Enhancement of gluonic dissociation of J/ψJ/\psi in viscous QGP

We have investigated the effect of viscosity on the gluonic dissociation of $J/\psi$ in an equilibrating plasma. Suppression of $J/\psi$ due to gluonic dissociation depend on the temperature and also on the chemical equilibration rate. In an equilibrating plasma, viscosity affects the temperature evolution and also the chemical equilibration rate, requiring both of them to evolve slowly compared to their ideal counter part. For Au+Au collisions at RHIC and LHC energies, gluonic dissociation of $J/\psi$ increases for a viscous plasma. Low $P_T$ $J/\psi$'s are found to be more suppressed due to viscosity than the high $P_T$ ones. Also the effect is more at LHC energy than at RHIC energy.Comment: 3 pages, 1 figur

Free-jet acoustic investigation of high-radius-ratio coannular plug nozzles

The experimental and analytical results of a scale model simulated flight acoustic exploratory investigation of high radius ratio coannular plug nozzles with inverted velocity and temperature profiles are summarized. Six coannular plug nozzle configurations and a baseline convergent conical nozzle were tested for simulated flight acoustic evaluation. The nozzles were tested over a range of test conditions that are typical of a Variable Cycle Engine for application to advanced high speed aircraft. It was found that in simulate flight, the high radius ratio coannular plug nozzles maintain their jet noise and shock noise reduction features previously observed in static testing. The presence of nozzle bypass struts will not significantly affect the acousticn noise reduction features of a General Electric type nozzle design. A unique coannular plug nozzle flight acoustic spectral prediction method was identified and found to predict the measured results quite well. Special laser velocimeter and acoustic measurements were performed which have given new insights into the jet and shock noise reduction mechanisms of coannular plug nozzles with regard to identifying further benificial research efforts

Exclusive charm production in pbar p collisions at s^1/2 <15 GeV

We discuss the open charm production in peripheral reactions $\bar pp\to \bar Y_cY_c$ and $\bar pp\to M_c\bar M_c$, where $Y_c$ and $M_c$ stand for $\Lambda_c^+,\Sigma_c^+$ and $D,D^*$, respectively, at $\sqrt{s}\lesssim 15$ GeV, which corresponds to the energy range of FAIR. Our consideration is based on the topological decomposition of the planar quark and diquark diagrams which allows to estimate consistently meson and baryon exchange trajectories and energy scale parameters as well. The spin dependence is determined by the effective interaction of lowest exchanged resonance. Unknown parameters are fixed by an independent analysis of open strangeness production in $\bar pp\to \bar YY$ and $\bar pp\to \bar KK$ reactions and of SU(4) symmetry. We present the corresponding cross sections and longitudinal double-spin asymmetries for exclusive binary reactions with open charm mesons and baryons in the final state. The polarization observables have a non-trivial $t$ and $s$ dependence which is sensitive to details of the open charm production mechanism.Comment: 26 pages, 18 figure

Statistical hadronization of charm at SPS, RHIC and LHC

We study the production of charmonia and charmed hadrons for nucleus-nucleus collisions at SPS, RHIC, and LHC energies within the framework of the statistical hadronization model. Results from this model are compared to the observed centrality dependence of J/psi production at SPS energy. We further provide predictions for the centrality dependence of the production of open and hidden charm mesons at RHIC and LHC.Comment: Contribution to Quark Matter 2002, 4 pages, 3 figures; revised version including charmed hyperons (omitted in v1

Pacman (II): Application and Statistical Characterisation of Improved RM Maps

We proposed a new method -- "Pacman" -- to calculate Faraday rotation measure (RM) maps from multi-frequency polarisation angle data (Dolag et al.) in order to avoid the so-called n-pi ambiguity. Here, we apply our "Pacman" algorithm to two polarisation data sets of extended radio sources in the Abell 2255 and the Hydra A cluster, and compare the RM maps obtained using "Pacman" to RM maps obtained employing already existing methods. Thereby, we provide a new high quality RM map of the Hydra north lobe which is in a good agreement with the existing one but find significant differences in the case of the south lobe of Hydra A. We demonstrate the reliability and the robustness of "Pacman". In order to study the influence of map making artefacts, which are imprinted by wrong solutions to the n-pi ambiguities, and of the error treatment of the data, we calculated and compared magnetic field power spectra from various RM maps. The power spectra were derived using the method recently proposed by Ensslin & Vogt (2003). We demonstrate the sensitivity of statistical analysis to artefacts and noise in the RM maps and thus, we demonstrate the importance of an unambiguous determination of RM maps and an understanding of the nature of the noise in the data. We introduce and perform statistical tests to estimate the quality of the derived RM maps, which demonstrate the quality improvements due to "Pacman".Comment: revised version, accepted, MNRAS in pres

Parton distributions of real and virtual photons

Recent progress on the parton distribution functions of the photon, both real and virtual, is briefly reviewed and experimental possibilities at HERA are discussed.Comment: 10 pages, LaTeX, 4 eps figures included in file using filecontents environment