10,290 research outputs found
Transverse energy distributions and production in Pb+Pb collisions
We have analyzed the latest NA50 data on transverse energy distributions and
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
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 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
dissociation on pion and -meson comovers in relativistic heavy ion
collisions. We find a substantial dependence of the absorption rates
on the density and temperature of the nuclear matter. This suggests that a
quantitative analysis of 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 via the
decay channel and at via the 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 in p+p collisions
are presented and future prospects for , and
measurements are discussed.Comment: 4 pages, 2 figures, Proceedings for Quark Matter 200
Enhancement of gluonic dissociation of in viscous QGP
We have investigated the effect of viscosity on the gluonic dissociation of
in an equilibrating plasma. Suppression of 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 increases for a viscous plasma.
Low 's are found to be more suppressed due to viscosity than the
high 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
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
Exclusive charm production in pbar p collisions at s^1/2 <15 GeV
We discuss the open charm production in peripheral reactions
and , where
and stand for and
, respectively, at 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 and 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 and dependence which is
sensitive to details of the open charm production mechanism.Comment: 26 pages, 18 figure
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
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