255 research outputs found

    A class of stochastic algorithms for the Wigner equation

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    A class of stochastic algorithms for the numerical treatment of the Wigner equation is introduced. The algorithms are derived using the theory of pure jump processes with a general state space. The class contains several new algorithms as well as some of the algorithms previously considered in the literature. The approximation error and the efficiency of the algorithms are analyzed. Numerical experiments are performed in a benchmark test case, where certain advantages of the new class of algorithms are demonstrated

    Towards Neutron Transformation Searches

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    To probe the origins of the baryon asymmetry, baryon number violation, the last unconfirmed Sakharov condition, must be definitively observed experimentally. Similarly, the nature of dark matter is currently unknown, and calls out for new candidates to be investigated. Each of these issues can be considered through the study of neutron transformations. Some rare baryon number violating processes, such as neutron-antineutron transformations, are expected to probe baryogenesis. Here, I show progress on this discovery target through construction of more accurate Monte Carlo models, the design of future detectors, creation of more complete atmospheric neutrino background simulations, and use of automated analysis techniques within the the NNBAR/HIBEAM experimental program at the European Spallation Source (ESS) and the Deep Underground Neutrino Experiment (DUNE). First simulation-based sensitivities for these experiments will be discussed. Modeling of rare neutron-antineutron transformation and subsequent annihilation will be discussed at length for multiple nuclei useful to these and other collaborations. To go along with this work, more comprehensive lepton-scattering nuclear models must be integrated into neutrino event generators for proper atmospheric neutrino background simulations. I discuss the first furnishing of these backgrounds for DUNE, and I highlight a potential path forward for the community in this vein using precision electron scattering modeling as a facsimile. Aspects of other potentially related neutron--mirror-neutron oscillations pertinent to dark matter and the neutron lifetime anomaly will also be considered for the ESS HIBEAM experiment. Here, I will present the first experimental sensitivity calculations for a broad range of modular experimental setups which will serve as research and design stepping stones toward NNBAR while producing a multitude of physics results over short time scales

    Production of Σ(1385)± and Ξ(1530)0 in proton-proton collisions at √s = 7 TeV

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    The production of the strange and double-strange baryon resonances (Sigma (1385)(+/-), Xi (1530)(0)) has been measured at mid-rapidity (vertical bar y vertical bar < 0.5) in proton-proton collisions at root s = 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the phi (1860) pentaquark, decaying in the Xi pi channel, has been carried out but no evidence is seen

    Production of Σ(1385)± and Ξ(1530)0 in proton–proton collisions at s√= 7 TeV

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    The production of the strange and double-strange baryon resonances (Σ(1385)±, Ξ(1530)0) has been measured at mid-rapidity (|y|<0.5) in proton–proton collisions at s√ = 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the ϕ(1860) pentaquark, decaying in the Ξπ channel, has been carried out but no evidence is seen.Funded by SCOAP

    Production of Σ(1385)±\Sigma(1385)^{\pm} and Ξ(1530)0\Xi(1530)^{0} in proton-proton collisions at s=\sqrt{s}= 7 TeV

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    The production of the strange and double-strange baryon resonances (Σ(1385)±\Sigma(1385)^{\pm}, Ξ(1530)0\Xi(1530)^{0}) has been measured at mid-rapidity (y<0.5\left | y \right |<0.5) in proton-proton collisions at s\sqrt{s} = 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the ϕ(1860)\phi(1860) pentaquark, decaying in the Ξπ\Xi\pi channel, has been carried out but no evidence is seen.Comment: 29 pages, 9 captioned figures, 9 tables, authors from page 24, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/193

    Study of the strange resonance sigma (1385) as a tool for the analysis of the dynamics of the Quark Gluon Plasma in the ALICE experiment at LHC

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    2009/2010La presente tesi si basa sul lavoro da me e ettuato nell'ambito della collaborazione ALICE. L'obiettivo scientifi co principale dell'esperimento é quello di investigare le proprietà della materia fortemente interagente fino alle elevatissime densità di energia (> 10 GeV/fm^3) e temperatura (~ 0.2 GeV) che verranno fornite da LHC e che ci si aspetta caratterizzino il mezzo formato nelle collisioni tra ioni pesanti a questi regimi. Calcoli di Cromo Dinamica Quantistica (QCD) su reticolo prevedono che in tali condizioni, il confi namento dei quark in adroni privi di carica di colore scompaia e si formi un plasma di quark e gluoni, denominato Quark-Gluon Plasma (QGP). Nelle ultime due decadi, numerose indicazioni della formazione di questo stato della materia sono state osservate negli esperimenti al CERN-SPS ( sqrt{s_{NN}} = 17.3 GeV) e al BNL-RHIC ( sqrt{s_{NN}} = 200 GeV). ALICE, quindi, grazie alle energie con cui opera e potrà operare in futuro, aprirà una porta in un regime totalmente nuovo e sinora inesplorato nel campo della sica delle interazioni forti. Il primo capitolo della tesi descrive per linee generali i fondamenti della QCD descrivendo le basi della sica del Plasma di Quark e Gluoni. Si so erma quindi nella descrizione di grandezze caratteristiche del tipo di fisica sotto esame e delle osservabili (probes) che possono testimonare la comparsa del QGP nelle collisioni fra ioni pesanti, con attenzione particolare riguardo a quelle legate alla produzione di stranezza. Vengono inoltre illustrati alcuni dei risultati principali ottenuti dagli esperimenti all'SPS e a RHIC nonché alcune delle primissime misure e ffettuate da ALICE. Nel secondo capitolo é presentata una breve descrizione della macchina LHC seguita da un'ampia panoramica delle varie componenti del rivelatore ALICE, delle rispettive prestazioni, nonché del framework di calcolo messo a punto per la gestione e l'analisi dell'enorme mole di dati prodotti dall'esperimento. Il terzo capitolo approfondisce in maniera piú specifi ca uno degli aspetti piú rilevanti della fi sica studiata da ALICE, ovvero la fi sica delle risonanze strane quale strumento per lo studio della evoluzione dinamica del QGP, in particolare durante la fase di ra reddamento. Tra le numerose risonanze strane oggetto di possibile indagine, alcuni modelli teorici conferiscono particolare rilevanza alla risonanza Sigma(1385) della quale verrano discusse le caratteristiche e gli studi che la concernono eff ettuati dall'esperimento STAR a RHIC. Il quarto capitolo entra quindi nell'ambito speci fico del lavoro svolto per questa tesi, ovvero lo studio della Sigma(1385) in ALICE, in collisioni protone-protone, nel canale di decadimento forte Lambda-pi. Verranno dapprima illustrati gli studi eff ettuati su simulazioni protone-protone all'energia di 10 TeV nel centro di massa, realizzati al ne di mettere a punto la procedura di analisi. Saranno descritte la procedura implementata per l'estrazione del segnale, la valutazione del fondo ed il fi t ai dati, nonché lo studio portato avanti per l'ottimizzazione dei tagli implementati al fine di massimizzare il rapporto segnale su rumore e la valutazione delle incertezze sistematiche. Il quinto ed ultimo capitolo illustrerà l'applicazione delle procedure descritte ai dati raccolti in collisioni protone-protone alle energie di 900 GeV e 7 TeV nel centro di massa, analisi fondamentale per il tuning dei modelli esistenti nonché come riferimento per le analisi in collisioni piombo-piombo che non rientrano nell'ambito di questa tesi. I tagli applicati sono stati quindi nuovamente ottimizzati in modo da verificare la bontà del metodo messo a punto su dati simulati e sono state valutate le incertezze sistematiche. Il capitolo termina con l'illustrazione dei risultati ottenuti. Dapprima i valori di massa e larghezza estratti dalle distribuzioni integrali in massa invariante, riscontrati in accordo con i valori riportati nel Particle Data Book; poi gli spettri di fferenziali in funzione del momento e della massa trasversi opportunamente ttati. I risultati vengono infine confrontati sia con le simulazioni prodotte alla medesima energia realizzate sulla base di diversi modelli teorici sia, in via del tutto preliminare, con i risultati ottenuti da STAR a sqrt{s} = 200 GeV.This thesis work was carried out in the context of the ALICE collaboration. The ALICE (A Large Ion Collider Experiment) experiment will study Pb-Pb collisions at the Large Hadron Collider (LHC) until the center of mass energy per nucleon pair sqrt{s_{NN}} = 5.5 TeV, the highest ever reached. The main physics goal of the experiment is the creation and the investigation of the properties of the strongly-interacting matter in the conditions of high energy density (> 10 GeV/fm^3) and high temperatures (~ 0.2 GeV), expected to characterize the medium formed in central heavy-ion collisions at these energies. Under these conditions, according to lattice Quantum Chromo Dynamics (QCD) calculations, quark confinement into colorless hadrons should fade and a deconfined Quark-Gluon Plasma (QGP) should be formed. In the past two decades, experiments at CERN-SPS ( sqrt{s_{NN} = 17.3 GeV) and BNL-RHIC ( sqrt{s_{NN} = 200 GeV) have gathered ample evidences for the formation of this state of matter. ALICE, therefore, thanks to the energies available now and in the next future, will open a door in a whole and completely unexplored new regime for the physics of the strong interactions. The first chapter of this thesis describes at a general level the cornerstones of the QCD and of the Quark-Gluon Plasma physics. Then it concentrates on the description of the main quantities related to the topics under analysis and on the so-called probes of the creation of the QGP in heavy-ion collisions. Particular attention will be put on the strangeness production related probes. Moreover some of the most important results obtained by the experiments at SPS and RHIC will be presented together with the very first measurements performed by ALICE. A very short description of the LHC machine and its features opens the second chapter followed by a wide overview of the ALICE detector and of its performances, in addiction with a description of the computing framework built for the collection and the analysis of the huge amount of data provided by the experiment. The third chapter will describe in more details one of the most relevant aspects of the physics studied by ALICE, i.e. the physics of the strange resonances as fundamental tool for the QGP dynamic evolution analysis, in particular during the freeze-out phase. Among them, some theoretical models consider much relevant the Sigma(1385). It will be described in detail, with particular attention to the studies performed on it by the STAR experiment at RHIC. The forth chapter is dedicated to this specific topic, i.e. the Sigma(1385) study at ALICE in proton-proton collisions, in the strong decay channel Lambda-pi. First of all the studies performed on simulated data at sqrt{s} = 10 TeV will be described. They were realized in order to built a dedicated analysis procedure. The implemented method for the signal extraction, background evaluation and the data fit will be described together with the optimized cuts introduced in order to find an optimal set able to maximize the signal over background ratio. Then the systematic uncertainties evaluation is presented. The application of the described procedure to the data collected in proton-proton collisions at sqrt{s} = 900 GeV and 7 TeV, is then presented in the fifth and last chapter. This analysis is crucial for the tuning of the existing models and is an important benchmark for the next lead-lead collisions analysis. A new cut optimization will be performed in order to check the consistence of the procedure built using the simulated data. The systematic uncertainties will be evaluated at both energies. The results obtained (both integral and di erential in the transverse momentum) will be shown and discussed together with a comparison with some dedicated simulations provided at the same energy with different models and with a very preliminary comparison with the STAR results at sqrt{s} = 200 GeV.XXIII Ciclo198
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