2,476 research outputs found
Mass modification of D-meson in hot hadronic matter
We evaluate the in-medium and -meson masses in hot hadronic
matter induced by interactions with the light hadron sector described in a
chiral SU(3) model. The effective Lagrangian approach is generalized to SU(4)
to include charmed mesons. We find that the D-mass drops substantially at
finite temperatures and densities, which open the channels of the decay of the
charmonium states (, , ) to pairs in
the thermal medium. The effects of vacuum polarisations from the baryon sector
on the medium modification of the -meson mass relative to those obtained in
the mean field approximation are investigated. The results of the present work
are compared to calculations based on the QCD sum-rule approach, the
quark-meson coupling model, chiral perturbation theory, as well as to studies
of quarkonium dissociation using heavy quark potential from lattice QCD.Comment: 18 pages including 7 figures, minor revision of the text, figure
styles modified, to appear in Phys. Rev.
A model-independent analysis of the dependence of the anomalous J/psi suppression on the number of participant nucleons
A recently published experimental dependence of the J/psi to Drell-Yan ratio
on the measured, by a zero degree calorimeter, forward energy E_ZDC in Pb+Pb
collisions at the CERN SPS is analyzed. Using a model-independent approach it
is shown that the data are at variance with an earlier published experimental
dependence of the same quantity on the transverse energy of neutral hadrons
E_T. The discrepancy is related to a moderate centrality region: 100 < N_p <
200 (N_p is the number of participant nucleons) and is peculiar only to the
data obtained within the `minimum bias' analysis (using the `theoretical
Drell-Yan'). This could result from systematic experimental errors in the
minimum bias sample. A possible source of the errors is discussed.Comment: 10 pages, LaTeX, 3 PS-figures. V2: Misprints are correcte
X-ray grating interferometry design for the 4D GRAPH-X system
The 4D GRAPH-X (Dynamic GRAting-based PHase contrast x-ray imaging) project aims at developing a prototype of an x-ray grating-based phase-contrast imaging scanner in a laboratory setting, which is based on the Moire single-shot acquisition method in order to be optimized for analysing moving objects (in the specific case, a dynamic thorax phantom), that could evolve into a suitable tool for biomedical applications although it can be extended to other application fields. When designing an x-ray Talbot-Lau interferometer, high visibility and sensitivity are two important figures of merit, strictly related to the performance of the system in obtaining high quality phase contrast and dark-field images. Wave field simulations are performed to optimize the setup specifications and construct a high-resolution and high-sensitivity imaging system. In this work, the design of a dynamic imaging setup using a conventional milli-focus x-ray source is presented. Optimization by wave front simulations leads to a symmetric configuration with 5.25 mu m pitch at third Talbot order and 45 keV design energy. The simulated visibility is about 22%. Results from GATE based Monte Carlo simulations show a 19% transmission percentage of the incoming beam into the detector after passing through all the gratings and the sample. Such results are promising in view of building a system optimized for dynamic imaging
Characterisation of silicon strip detectors with a binary readout chip for X-ray imaging
In this paper we describe the development of a multichannel readout system for X-ray measurements using silicon strip detectors. The developed system is based on a binary readout architecture and optimised for detection of X-rays of energies in the range 6}30 keV. The critical component of the system is the 32-channel front-end chip, RX32N, which has been optimised for low noise performance, small channel to channel variation and high counting rate operation. The performance of the chip is demonstrated by measurements of complex X-ray spectra using silicon strip and pad detectors. The obtained results allow to use the system at room temperature with the detection threshold in the range from 500 to 10 000 electrons, which is enough in many crystallographic and medical imaging applications. ( 2000 Elsevier Scienc
Dual energy imaging in mammography: Cross-talk study in a Si array detector
Abstract One of the main limitation to the extensive use of breast-cancer screening as a prevention method is the relatively high X-ray dose released to the patient. A new approach is under study in which two quasi-monochromatic beamswith mean energies of 18.0 and 36.0 keV -are produced simultaneously, starting from an X-ray tube, by means of a monochromator based on a pyrolytic graphite crystal. The two beams are superimposed in space. The removal of the energy components with low content of diagnostic information from the spectrum, leads to a reduction of the dose released to patients maintaining (or improving) the image quality. The two quasi-monochromatic beams impinge on the patient and then are detected with a solid-state array detector; the image results as the difference between the transmitted intensities of the two detected beams. In this work, the performances of two different electronic readouts and three pixel widths of a silicon position sensitive array detector are simulated and described in order to minimize cross-talk effects between adjacent pixels. The use of a detector with spectrometric capabilities is necessary to separate, by means of thresholds, the high energy photons from the low energy ones
J/psi azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158 GeV per nucleon
The J/ azimuthal distribution relative to the reaction plane has been
measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various
physical mechanisms related to charmonium dissociation in the medium created in
the heavy ion collision are expected to introduce an anisotropy in the
azimuthal distribution of the observed J/ mesons at SPS energies. Hence,
the measurement of J/ elliptic anisotropy, quantified by the Fourier
coefficient v of the J/ azimuthal distribution relative to the
reaction plane, is an important tool to constrain theoretical models aimed at
explaining the anomalous J/ suppression observed in Pb-Pb collisions. We
present the measured J/ yields in different bins of azimuthal angle
relative to the reaction plane, as well as the resulting values of the Fourier
coefficient v as a function of the collision centrality and of the
J/ transverse momentum. The reaction plane has been estimated from the
azimuthal distribution of the neutral transverse energy detected in an
electromagnetic calorimeter. The analysis has been performed on a data sample
of about 100 000 events, distributed in five centrality or p
sub-samples. The extracted v values are significantly larger than zero
for non-central collisions and are seen to increase with p.Comment: proceedings of HP08 conference corrected a typo in one equatio
The dependence of the anomalous J/psi suppression on the number of participant nucleons
The observation of an anomalous J/psi suppression in Pb-Pb collisions by the NA50 Collaboration can be considered as the most striking indication for the deconfinement of quarks and gluons at SPS energies. In this Letter, we determine the J/psi suppression pattern as a function of the forward hadronic energy E-ZDC measured in a Zero Degree Calorimeter (ZDC). The direct connection between EZDC and the geometry of the collision allows us to calculate, within a Glauber approach, the precise relation between the number of participant nucleons N-part and E-ZDC. Then, we check if the experimental data can be better explained by a sudden or a smooth onset of the anomalous J/psi suppression as a function of the number of participants. (C) 2001 Elsevier Science B.V. All rights reserved.info:eu-repo/semantics/publishedVersio
A new measurement of J/psi suppression in Pb-Pb collisions at 158 GeV per nucleon
We present a new measurement of J/psi production in Pb-Pb collisions at 158
GeV/nucleon, from the data sample collected in year 2000 by the NA50
Collaboration, under improved experimental conditions with respect to previous
years. With the target system placed in vacuum, the setup was better adapted to
study, in particular, the most peripheral nuclear collisions with unprecedented
accuracy. The analysis of this data sample shows that the (J/psi)/Drell-Yan
cross-sections ratio measured in the most peripheral Pb-Pb interactions is in
good agreement with the nuclear absorption pattern extrapolated from the
studies of proton-nucleus collisions. Furthermore, this new measurement
confirms our previous observation that the (J/psi)/Drell-Yan cross-sections
ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb
collisions and that this ratio persistently decreases up to the most central
collisions.Comment: 19 pages, 10 figures. Submitted to Eur. Phys. J.
Heavy Quarkonium Physics
This report is the result of the collaboration and research effort of the
Quarkonium Working Group over the last three years. It provides a comprehensive
overview of the state of the art in heavy-quarkonium theory and experiment,
covering quarkonium spectroscopy, decay, and production, the determination of
QCD parameters from quarkonium observables, quarkonia in media, and the effects
on quarkonia of physics beyond the Standard Model. An introduction to common
theoretical and experimental tools is included. Future opportunities for
research in quarkonium physics are also discussed.Comment: xviii + 487 pages, 260 figures. The full text is also available at
the Quarkonium Working Group web page: http://www.qwg.to.infn.i
- …