Nuclear absorption of Charmoniums in pA and AA collisions

We have analysed the latest NA50 data on $J/\psi$ production in pA and AA collisions. The $J/\psi$ production is assumed to be a two step process, (i) formation of $c\bar{c}$ pairs, perturbatively calculable, and (ii) formation of $J/\psi$ from the pair, a non-perturbative process, which is conviniently parametrized. In a nuclear medium, as the $c\bar{c}$ 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 $J/\psi$ cross sectional data. The model then reproduces the centrality dependence of $J/\psi$ over Drell-Yan ration in 200 GeV/c S+U and 158 GeV/c Pb+Pb collisions. We also discuss the centrality dependence of $J/\psi$ 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 $J/\Psi$ 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 $J/\Psi$ 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 α(A,qT)\alpha(A,q_T) for the Drell-Yan and J/ψ\psi production

Define the nuclear dependence coefficient $\alpha(A,q_T)$ in terms of ratio of transverse momentum spectrum in hadron-nucleus and in hadron-nucleon collisions: $\frac{d\sigma^{hA}}{dq_T^2}/ \frac{d\sigma^{hN}}{dq_T^2}\equiv A^{\alpha(A,q_T)}$. We argue that in small $q_T$ region, the $\alpha(A,q_T)$ for the Drell-Yan and J/$\psi$ production is given by a universal function:\ $a+b q_T^2$, where parameters a and b are completely determined by either calculable quantities or independently measurable physical observables. We demonstrate that this universal function $\alpha(A,q_T)$ is insensitive to the A for normal nuclear targets. For a color deconfined nuclear medium, the $\alpha(A,q_T)$ becomes strongly dependent on the A. We also show that our $\alpha(A,q_T)$ for the Drell-Yan process is naturally linked to perturbatively calculated $\alpha(A,q_T)$ at large $q_T$ without any free parameters, and the $\alpha(A,q_T)$ is consistent with E772 data for all $q_T$.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 donn&eacute;es obtenues par radiom&egrave;tre perfectionn&eacute; &agrave; tr&egrave;s haute r&eacute;solution pour extraire des alb&eacute;dos &agrave; large bande de la surface de la glace &agrave; partir de luminances du sommet de l'atmosph&egrave;re du canal 1 et 2 &agrave; bande &eacute;troite. On applique aux donn&eacute;es par satellite des corrections pour l'atmosph&egrave;re interm&eacute;diaire, l'angle de prise de vue et la r&eacute;ponse spectrale des capteurs. La correction atmosph&eacute;rique augmente les alb&eacute;dos du sommet de l'atmosph&egrave;re de 27 &agrave; 32 p. cent. Apr&egrave;s avoir &eacute;limin&eacute; l'influence de l'angle de prise de vue, la variabilit&eacute; de l'alb&eacute;do de la surface entre les orbites diminue. L'alb&eacute;do de la surface obtenu par satellite sur la glace de mer couverte de neige apr&egrave;s correction pour l'angle de prise de vue allait de 0,68 &agrave; 0,82. On attribue la variabilit&eacute; r&eacute;siduelle diurne &agrave; des incertitudes dans les corrections atmosph&eacute;rique et anisotrope des donn&eacute;es obtenues par satellite. Apr&egrave;s comparaison avec des mesures correspondantes effectu&eacute;es in situ, les alb&eacute;dos obtenus &agrave; l'aide du radiom&egrave;tre perfectionn&eacute; &agrave; tr&egrave;s haute r&eacute;solution et corrig&eacute;s pour l'atmosph&egrave;re interm&eacute;diaire et l'angle de prise de vue concordaient d'assez pr&egrave;s avec les mesures effectu&eacute;es &agrave; la surface m&ecirc;me. La grande variabilit&eacute; dans les mesures de surface refl&egrave;te la difficult&eacute; qu'il y a &agrave; mesurer les alb&eacute;dos de surface dans des r&eacute;gions correspondant &agrave; celles d'un pixel typique obtenu &agrave; l'aide d'un radiom&egrave;tre perfectionn&eacute; &agrave; tr&egrave;s haute r&eacute;solution. De fa&ccedil;on &agrave; d&eacute;velopper une m&eacute;thodologie fiable permettant d'utiliser ces donn&eacute;es par satellite pour obtenir l'alb&eacute;do de la glace de mer, on a besoin de mieux comprendre &agrave; la fois le comportement de l'atmosph&egrave;re sur les grandes longueurs de couloir communes &agrave; l'Arctique et la nature anisotrope de la r&eacute;flectance de la glace de mer couverte de neige. Il faut en outre tenir compte de toute caract&eacute;ristique saisonni&egrave;re pertinente &agrave; ces facteurs.Mots cl&eacute;s: glace de mer, alb&eacute;do, t&eacute;l&eacute;d&eacute;tection, radiom&egrave;tre perfectionn&eacute; &agrave; tr&egrave;s haute r&eacute;solution, 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