Simulation in ALICE

ALICE, the experiment dedicated to the study of heavy ion collisions at the LHC, uses an object-oriented framework for simulation, reconstruction and analysis (AliRoot) based on ROOT. Here, we describe the general ALICE simulation strategy and those components of the framework related to simulation. Two main requirements have driven the development of the simulation components. First, the possibility to run different transport codes with the same user code for geometry and detector response has led to the development of the Virtual Monte Carlo concept. Second, simulation has to provide tools to efficiently study events ranging from low-multiplicity pp collisions to Pb-Pb collisions with up to 80000 primary particles per event. This has led to the development of a variety of collaborating generator classes and specific classes for event merging.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, USA, March 2003, 6 pages, LaTeX, 5 eps figures. PSN TUMT00

Shear-free perfect fluids with a solenoidal electric curvature

We prove that the vorticity or the expansion vanishes for any shear-free perfect fluid solution of the Einstein field equations where the pressure satisfies a barotropic equation of state and the spatial divergence of the electric part of the Weyl tensor is zero.Comment: 9 page

Mutual information between reflected and transmitted speckle images

We study theoretically the mutual information between reflected and transmitted speckle patterns produced by wave scattering from disordered media. The mutual information between the two speckle images recorded on an array of N detection points (pixels) takes the form of long-range intensity correlation loops, that we evaluate explicitly as a function of the disorder strength and the Thouless number g. Our analysis, supported by extensive numerical simulations, reveals a competing effect of cross-sample and surface spatial correlations. An optimal distance between pixels is proven to exist, that enhances the mutual information by a factor Ng compared to the single-pixel scenario.Comment: 5 pages, 4 figures, + S

LA FORMAZIONE DEI GRUPPI PARLAMENTARI NELLA XVII LEGISLATURA: I GRUPPI COSTITUITI “DI DIRITTO” E LE LORO VICENDE INTERNE

L'articolo esamina i passaggi procedurali che hanno portato alla formazione dei gruppi parlamentari all'inizio della XVII legislatura e alla composizione degli Uffici di presidenza delle due Camere, offrendo una lettura critica della prassi che, per assecondare estemporanee esigenze politiche, rischia di favorire fenomeni di transfughismo parlamentare

La Corte costituzionale decide i ricorsi "Berlusconi" e "Mastella" in materia di reati ministeriali e "taglia i ponti" tra le Camere e l'autorità giudiziaria

L'articolo analizza le due decisioni con le quali la Corte costituzionale, nel 2012, ha risolto i conflitti sollevati dalle Assemblee legislative, in forza dell'art. 96 Cost, contro l'autorità giudiziaria penale che procedeva, secondo il rito ordinario, nei confronti di esponenti del Governo. L'A. trae spunto da alcune precisazioni contenute nella motivazione delle due sentenze per riflettere sull'applicabilità del principio di leale collaborazione ai rapporti fra magistratura e organi di indirizzo politico. Valuta inoltre criticamente la scelta della Corte di ritenere ammissibili ricorsi diretti a contestare la qualificazione dei reati imputati a ministri, ritenendo che in tali casi sia piuttosto il Governo, e non le Camere, l'organo legittimato al conflitto con l’autorità giudiziaria. Si sottolinea, infine, come la Corte costituzionale sembri prefigurare un sindacato sull'attività giurisdizionale insolitamente penetrante e come, dall'altro lato, si profili l'ipotesi di un controllo sulle motivazioni con le quali le Camere decidano di non autorizzare la celebrazione di processi per reati ministeriali che esse ritengano compiuti nell'interesse dello Stato

LA FORMAZIONE DEI GRUPPI PARLAMENTARI NELLA XVII LEGISLATURA: LA DEROGA CONCESSA AL MOVIMENTO POLITICO FRATELLI D’ITALIA E LE SUE RICADUTE IN TERMINI POLITICO-ORGANIZZATIVI

L'articolo esamina un caso di applicazione della deroga al requisito numerico previsto dai regolamenti per la costituzione di un gruppo parlamentare i e le ricadute che tale eccezione ha comportato sulla composizione e il funzionamento degli organi interni alla Camera dei deputati

ALICE experience with GEANT4

Since its release in 1999, the LHC experiments have been evaluating GEANT4 in view of adopting it as a replacement for the obsolescent GEANT3 transport MonteCarlo. The ALICE collaboration has decided to perform a detailed physics validation of elementary hadronic processes against experimental data already used in international benchmarks. In one test, proton interactions on different nuclear targets have been simulated, and the distribution of outgoing particles has been compared to data. In a second test, penetration of quasi-monoenergetic low energy neutrons through a thick shielding has been simulated and again compared to experimental data. In parallel, an effort has been put on the integration of GEANT4 in the AliRoot framework. An overview of the present status of ALICE GEANT4 simulation and the remaining problems will be presented. This document will describe in detail the results of these tests, together with the improvements that the GEANT4 team has made to the program as a result of the feedback received from the ALICE collaboration. We will also describe the remaining problems that have been communicated to GEANT4 but not yet addressed.Comment: 8 pages, 12 figures, for the CHEP03 conference proceeding

Near-field interactions and non-universality in speckle patterns produced by a point source in a disordered medium

A point source in a disordered scattering medium generates a speckle pattern with non-universal features, giving rise to the so-called C_0 correlation. We analyze theoretically the relationship between the C_0 correlation and the statistical fluctuations of the local density of states, based on simple arguments of energy conservation. This derivation leads to a clear physical interpretation of the C_0 correlation. Using exact numerical simulations, we show that C_0 is essentially a correlation resulting from near-field interactions. These interactions are responsible for the non-universality of C_0, that confers to this correlation a huge potential for sensing and imaging at the subwavelength scale in complex media