1,016 research outputs found
Nuclear absorption of Charmoniums in pA and AA collisions
We have analysed the latest NA50 data on production in pA and AA
collisions. The production is assumed to be a two step process, (i)
formation of pairs, perturbatively calculable, and (ii) formation of
from the pair, a non-perturbative process, which is conviniently
parametrized. In a nuclear medium, as the pair passes through the
nuclear medium, it gain relative square momentum and some of the pairs can gain
enough square momentum to cross the threshold for open charm meson, leading to
suppression in nuclear medium. Few parameters of the model were fixed from the
latest high statistics NA50 pA and NA38 SU total cross sectional data.
The model then reproduces the centrality dependence of over Drell-Yan
ration in 200 GeV/c S+U and 158 GeV/c Pb+Pb collisions. We also discuss the
centrality dependence of suppression at RHIC energy.Comment: 4 pages including 3 figures, Revised version, to be published in
Phys.Rev.
Percolation approach to quark gluon plasma in high energy pp collisions
We apply continuum percolation to proton-proton collisions and look for the
possible threshold to phase transition from confined nuclear matter to quark
gluon plasma. Making the assumption that J/Psi suppression is a good signal to
the transition, we discuss this phenomenon for pp collisions, in the framework
of a dual model with strings.Comment: 8 pages, 3 figure
J/Psi suppression in colliding nuclei: statistical model analysis
We consider the suppression at a high energy heavy ion collision. An
ideal gas of massive hadrons in thermal and chemical equilibrium is formed in
the central region. The finite-size gas expands longitudinally in accordance
with Bjorken law. The transverse expansion in a form of the rarefaction wave is
taken into account. We show that suppression in such an environment,
when combined with the disintegration in nuclear matter, gives correct
evaluation of NA38 and NA50 data in a broad range of initial energy densities.Comment: 14 pages, 13 figures. Accepted for publication in Phys. Rev.
Leakage Effect on J/psi Pt Distributions in Different Centrality Bins for Pb-Pb Collisions at E/A=160 GeV
A transport approach including a leakage effect for J/psi's in the transverse
phase space is used to calculate the ratios between the J/psi transverse
momentum distributions in several centrality bins for Pb-Pb collisions at E/A =
160 GeV. From the comparison with the CERN-SPS data, where the centrality is
characterized by the transverse energy Et, the leakage effect is extremely
important in the region of high transverse momentum and high transverse energy,
and both the threshold and the comover models can describe the ratio well for
all centrality bins except the most central one (Et < 100 GeV), for which the
comover model calculation is considerably better than the threshold one.Comment: 4 pages, 2 figures, REVTEX3.1, accepted for publication in Phys. Rev.
Nuclear dependence coefficient for the Drell-Yan and J/ production
Define the nuclear dependence coefficient in terms of ratio
of transverse momentum spectrum in hadron-nucleus and in hadron-nucleon
collisions: . We argue that in small region, the
for the Drell-Yan and J/ production is given by a universal function:\
, where parameters a and b are completely determined by either
calculable quantities or independently measurable physical observables. We
demonstrate that this universal function is insensitive to the
A for normal nuclear targets. For a color deconfined nuclear medium, the
becomes strongly dependent on the A. We also show that our
for the Drell-Yan process is naturally linked to perturbatively
calculated at large without any free parameters, and the
is consistent with E772 data for all .Comment: latex, 28 pages, 10 figures, updated two figures, and add more
discussion
Properties of an equilibrium hadron gas subjected to the adiabatic longitudinal expansion
We consider an ideal gas of massive hadrons in thermal and chemical
equilibrium. The gas expands longitudinally in an adiabatic way. This evolution
for a baryonless gas reduces to a hydrodynamic expansion. Cooling process is
parametrized by the sound velocity. The sound velocity is temperature dependent
and is strongly influenced by hadron mass spectrum.Comment: 7pages, 7 figures-- uucoded file of figures appended at the end,
separated from the paper by lines with many dashe
Questions and Answers in Extreme Energy Cosmic Rays – a guide to explore the data set of the Pierre Auger Observatory
The Pierre Auger Observatory is the largest extensive air shower detector, covering 3000 km 2 in Argentina. The Observatory makes available, for educational and outreach purposes, 1% of its cosmic ray data set, corresponding after 10 years of running to more than 35 000 cosmic ray events. Several different proposals of educational activities have been developed within the collaboration and are available. We will focus on the activity guide we developed with the aim of exploring the rich education and outreach potential of cosmic rays with Portuguese high school students. In this guide we use the Auger public data set as a starting point to introduce open questions on the origin, nature and spectrum of high energy cosmic rays. To address them, the students learn about the air-shower cascade development, data reconstruction and its statistical analysis. The guide has been used both in the context of student summer internships at research labs and directly in schools, under the supervision of trained teachers and in close collaboration with Auger researchers. It is now available in Portuguese, English and Spanish.Peer Reviewe
Coherence Time Effects on J/psi Production and Suppression in Relativistic Heavy Ion Collisions
Using a coherence time extracted from high precision proton-nucleus Drell-Yan
measurements and a nuclear absorption cross section extracted from pA
charmonium production experiments, we study J/psi production and absorption in
nucleus-nucleus collisions. We find that coherence time effects are large
enough to affect the measured J/psi-to-Drell-Yan ratio. The S+U data at 200A
GeV/c measured by NA38 are reproduced quantitatively without the introduction
of any new parameters. However, when compared with recent NA50 measurements for
Pb+Pb at 158A GeV/c, the data is not reproduced in trend or in magnitude.Comment: 8 pages, 2 figure
Comparison of In Situ and AVHRR-Derived Broadband Albedo over Arctic Sea Ice
Advanced Very High Resolution Radiometer (AVHRR) data are used to extract broadband sea ice surface albedos from narrowband channel 1 and 2 top of the atmosphere (TOA) radiances. Corrections for the intervening atmosphere, viewing geometry and sensor spectral response are applied to the satellite data. Atmospheric correction increases TOA albedos by 27 to 32%. After removing the effects of viewing geometry, surface albedo variability between orbits decreases. The satellite-derived surface albedo over snow-covered sea ice corrected for viewing geometry ranged from 0.68 to 0.82. The residual diurnal variability is attributed to uncertainties in the atmospheric and anisotropic corrections of the satellite data. After comparison with coincidental in situ measurements, AVHRR pixel. In order to develop a reliable methodology for using these satellite data to derive sea ice albedo, an improved understanding of both the atmosphere's behavior over the long path lengths common to the Arctic and the anisotropic nature of snow-covered sea ice reflectance is required. Furthermore, any seasonal characteristics of these factors must be addressed.Key words: sea ice, albedo, remote sensing, AVHRR, anisotropyOn utilise des données obtenues par radiomètre perfectionné à très haute résolution pour extraire des albédos à large bande de la surface de la glace à partir de luminances du sommet de l'atmosphère du canal 1 et 2 à bande étroite. On applique aux données par satellite des corrections pour l'atmosphère intermédiaire, l'angle de prise de vue et la réponse spectrale des capteurs. La correction atmosphérique augmente les albédos du sommet de l'atmosphère de 27 à 32 p. cent. Après avoir éliminé l'influence de l'angle de prise de vue, la variabilité de l'albédo de la surface entre les orbites diminue. L'albédo de la surface obtenu par satellite sur la glace de mer couverte de neige après correction pour l'angle de prise de vue allait de 0,68 à 0,82. On attribue la variabilité résiduelle diurne à des incertitudes dans les corrections atmosphérique et anisotrope des données obtenues par satellite. Après comparaison avec des mesures correspondantes effectuées in situ, les albédos obtenus à l'aide du radiomètre perfectionné à très haute résolution et corrigés pour l'atmosphère intermédiaire et l'angle de prise de vue concordaient d'assez près avec les mesures effectuées à la surface même. La grande variabilité dans les mesures de surface reflète la difficulté qu'il y a à mesurer les albédos de surface dans des régions correspondant à celles d'un pixel typique obtenu à l'aide d'un radiomètre perfectionné à très haute résolution. De façon à développer une méthodologie fiable permettant d'utiliser ces données par satellite pour obtenir l'albédo de la glace de mer, on a besoin de mieux comprendre à la fois le comportement de l'atmosphère sur les grandes longueurs de couloir communes à l'Arctique et la nature anisotrope de la réflectance de la glace de mer couverte de neige. Il faut en outre tenir compte de toute caractéristique saisonnière pertinente à ces facteurs.Mots clés: glace de mer, albédo, télédétection, radiomètre perfectionné à très haute résolution, anisotropi
New bounds for Tsallis parameter in a noncommutative phase-space entropic gravity and nonextensive Friedmann equations
In this paper, we have analyzed the nonextensive Tsallis statistical
mechanics in the light of Verlinde's formalism. We have obtained, with the aid
of a noncommutative phase-space entropic gravity, a new bound for Tsallis
nonextensive (NE) parameter (TNP) that is clearly different from the ones
present in the current literature. We derived the Friedmann equations in a NE
scenario. We also obtained here a relation between the gravitational constant
and the TNP.Comment: 15 pages. Final version to appear in Physica
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