Dissertationen zum Thema „Quarks“
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1
Caron, Huot Simon 1984. „Heavy quark energy losses in the quark-gluon plasma : beyond leading order“. Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112385.
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We compute, to next-to-leading order in perturbation theory, the rate of energy loss suffered by a heavy quark moving nonrelativistically in the quark-gluon plasma. This quantity is essentially a measure of the scattering rates of this quark against plasma constituents, and of their efficiency in slowing it down. The next-to-leading order correction is sensitive to the physics of overlapping scatterings, as well as to the self-interactions of gauge fields with small momenta (of order the electric screening scale). We find the next-to-leading order correction to be remarkably large, suggesting that the perturbative series is unreliable unless the coupling constant of the theory assumes unrealistically small values.
2
BASTOS, Cristiano Costa. „Química com quarks“. Universidade Federal de Pernambuco, 2007. https://repositorio.ufpe.br/handle/123456789/8777.
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Previous issue date: 2007Algumas propriedades da química de quarks podem ser obtidas realizando cálculos ab initio Hartree-Fock para átomos com carga nuclear fracionária e moléculas formadas por estes átomos. Obtivemos o estado fundamental e o primeiro estado excitado para os átomos de sódio, lítio, berílio e magnésio interagentes com quarks. Isto sugere que transições eletrônicas podem ser usadas como guia para detecção de quarks livres. Analisamos a variação da energia de ligação eletrônica com a carga nuclear para as séries isoeletrônicas de átomos com carga nuclear fracionária A±2/3 e A±1/3 (A = H, Li, Na, P and Ca). Isto mostra que partículas de cor não confinadas preferem se ligar a átomos pesados e o par quark-antiquark pode ser estabilizado na presença da matéria atômica
3
Wünsch, Rudi, und Mathias Schleif. „The Chiral Quark-Loop Soliton in a Hot Gas of Constituent Quarks“. Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-31115.
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We consider a chiral one-loop hedgehog soliton of the bosonized SU(2)f Nambu & Jona-Lasinio model which is embedded in a liot medium of constituent quarks. Energy and radius of the soliton are determined in self-consistent mean-field approximation. Quasi-classical corrections to the soliton energy are derived by means of the pushing and cranking approaches. The corresponding inertial parameters are evaluated. It is shown that the inertial mass is equivalent to the total internal energy of the soliton. Corrected nucleon and ∆ isobar masses are calculated in dependence on temperature and density of the medium. As a result of the internal structure of the soliton which is controlled by the self-consistent mean field, the scaling between constituent quark mass and soliton mass is noticeable disturbed.
4
Wünsch, Rudi, und Mathias Schleif. „The Chiral Quark-Loop Soliton in a Hot Gas of Constituent Quarks“. Forschungszentrum Rossendorf, 1997. https://hzdr.qucosa.de/id/qucosa%3A21938.
Annotation:
We consider a chiral one-loop hedgehog soliton of the bosonized SU(2)f Nambu & Jona-Lasinio model which is embedded in a liot medium of constituent quarks. Energy and radius of the soliton are determined in self-consistent mean-field approximation. Quasi-classical corrections to the soliton energy are derived by means of the pushing and cranking approaches. The corresponding inertial parameters are evaluated. It is shown that the inertial mass is equivalent to the total internal energy of the soliton. Corrected nucleon and ∆ isobar masses are calculated in dependence on temperature and density of the medium. As a result of the internal structure of the soliton which is controlled by the self-consistent mean field, the scaling between constituent quark mass and soliton mass is noticeable disturbed.
5
Smith, Jason. „Quarks and antiquarks in nuclei /“. Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9750.
6
Veiga, J. S. „Propriedades da matéria nuclear em modelos de quarks constituintes /“. São Paulo, 1996. http://hdl.handle.net/11449/132865.
7
Devlin, Francis Robert. „Physics of heavy quarks“. Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319786.
8
Julien, Jean Marc. „Structure du noyau, particules élémentaires : Les quarks : ultimes entités de la matière“. Paris 5, 1988. http://www.theses.fr/1988PA05P060.
9
Leyva, Alfonso. „Strahlungskorrekturen zu Polarisationsobservablen schwerer Quarks“. [S.l. : s.n.], 2000. http://ArchiMeD.uni-mainz.de/pub/2000/0128/diss.pdf.
10
Higuchi, Katsuichi. „Electroweak Interaction with Singlet Quarks“. 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/152527.
11
Sánchez, Carlos Andrés. „Measurement of the Top Quark Mass with Neural Networks“. The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1039046089.
12
Coci, Gabriele. „Probing the Quark-Gluon Plasma properties through Heavy Quarks' dynamics: transport coefficients and elliptic flow“. Doctoral thesis, Università di Catania, 2018. http://hdl.handle.net/10761/4190.
Annotation:
Quantum Chromodynamics (QCD) is the non-abelian gauge field theory that within the Standard Model describes the strong interaction between quarks and gluons. QCD exhibits two main properties:confinement and asymptotic freedom. The former implies that in ordinary matter quarks and gluons are bounded within colorless hadrons. The latter is related to the decrease of the QCD strength coupling with increasing characteristic energy of the process. Asymptotic freedom implies that under extreme conditions of high temperature and density the interaction affecting quarks and gluons is so weakly that they are released from the bounding state to form a deconfined phase of matter known as the Quark-Gluon Plasma (QGP). Numerical solutions of QCD equations on lattice (lQCD) predict that such transition is properly a crossover at almost zero baryon density and with a critical temperature Tc=155 MeV. The study of nuclear matter under extreme conditions is the main program of the experiments at the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) where ultrarelativistic Heavy-Ion Collisions (HICs) are conducted to create an almost baryon free QGP with initial T = 3Tc. In this scenario Heavy Quarks (HQs), mainly charm and bottom, play a unique role. Due to their large masses HQs are created at the initial stage of HICs by hard perturbative QCD scattering processes. Moreover, their thermalization time is comparable with the QGP lifetime. Hence HQs can probe the entire evolution of the fireball carrying more information about their initial properties. The most important observables in the HQ sector are the nuclear modification factor RAA and the elliptic flow v2. The challenge of each theoretical framework is to provide a simultaneous description of these two observables that have been measured both at RHIC and LHC energies.
In this thesis we study the HQ dynamics within the QGP by means of a relativistic Boltzmann transport approach. In this framework we treat non-perturbative QCD effects by prescription of a Quasi-Particle Model (QPM) in which light quarks and gluons of the bulk are dressed with effective masses and the T dependence of the strength coupling is fitted to lQCD thermodynamics.
In the first part of this thesis we discuss HQ transport coefficients by performing simulations in static QCD medium. We compare our extracted drag and diffusion coefficients with results obtained through a Montecarlo integration. Afterwards, we investigate charm suppression and compare the results among various theoretical models.
In the second part, we focus on the dynamical evolution of HQs within the QGP by carrying out simulations of realistic HICs. We observe that within our QPM interaction, which implies a T-dependent drag coefficient almost constant near Tc, we are able to describe simultaneously the RAA and v2 of D mesons both at RHIC and LHC energies. In order to compare with the experimental measurements we couple the final HQ spectra to a hybrid coalescence plus fragmentation hadronization model which is suitable to describe the large magnitude of the observed charmed baryon-to-meson ratio.
In the same framework, we provide our predictions for B meson RAA and v2 and compare our results with the available experimental data.
A goal of this work is to include the effect of enhanced baryon production in HICs on the nuclear modification factor.
Finally, we present our estimate of the HQ spatial diffusion coefficient Ds(T) within our Boltzmann approach. We show that our phenomenological predictions of Ds for charm quark are in agreement with lQCD expectations, meaning that through the study of HQ thermalization we can probe the QCD interaction within the present uncertainties of lQCD. We point out also that the possibility to calculate transport coefficients at the bottom mass scale allows to reduce uncertainties coming from the adopted transport model and to bring the estimate of Ds closer to the quenched lQCD.
13
Guiot, Benjamin. „Production de charms et de photons prompts avec le générateur d'évènements EPOS“. Thesis, Nantes, Ecole des Mines, 2014. http://www.theses.fr/2014EMNA0192/document.
Annotation:
Au LHC, la collision de particules de très hautes énergies permet d’étudier l’interaction forte. En particulier, lors de la collision de deux noyaux (de plomb pour le LHC), un nouvel état de la matière, appelé Plasma de Quarks Gluons (QGP), est créé. L’étude de ce QGP constitue actuellement un des domaines actif de la recherche en physique. Les sondes dures, telles les quarks lourds ou les photons prompts, sont produit dés les premiers instants des collisions faites au LHC. Cette caractéristique les rend idéales pour l’étude du QGP. Elles vont traverser et interagir avec le milieu créé. En comparant avec un cas sans QGP (collisions proton-proton), il sera possible d’évaluer l’influence du plasma sur ces sondes dures et d’en extraire les propriétés telles la température et la densité. Cette étude nécessite donc d’avoir une bonne connaissance de la production de ces sondes dures dans les collisions proton-proton. Le but de ma thèse est l’implémentation des quarks lourds et des photons prompts dans le générateur d’évènements EPOS (codes informatique simulant les collisions), pour les collisions p-p. Le but final sera d’utiliser ce travail pour l’étude du plasma dans les collisions Pb-PbAt the LHC, strong interaction is studied by doing collisions of high energy particles. In the case of nucleus-nucleus collision (lead at the LHC), a new state of matter, called Quarks Gluons Plasma (QGP), is created. The study of this QGP is currently a lively research field. Hard probes, like heavy quarks and prompt photons, are produced during early times of collisions done at the LHC. This is why they are ideal probes for the study of the QGP. They will go through and interact with the medium produced by the collision. A comparison with a case without QGP (proton-proton- collision) will allow us to see how hard probes properties are modified by themedium. Then, medium properties like temperature and density can be extracted. This study requires a good understanding of hard probes production in proton-proton collisions. The aim of my thesis is the implementation of heavy quarks and prompt photons in the event generator EPOS (computer code for colliders), for p-p collisions. Our final aim is the study of the QGP in Pb-Pb collisions
14
Hadjimichef, Dimiter. „Formalismo de Fock-Tani para a física hadrônica /“. São Paulo, 1995. http://hdl.handle.net/11449/132802.
Annotation:
Orientador: Gastão Inácio KreinBanca: Mahir Saleh Hussein
Banca: Yogiro Hama
Banca: Eliane Angela Veit
Banca: Rogério Rosenfeld
Resumo: O formalismo de teoria de campos Fock-Tani, o qual foi originalmente desenvolvido na física atômica para tratar sistemas em que os graus de liberdade internos dos átomos não podem ser desprezados, é generalizado para sistemas de hádrons compostos. Partindo da representação no espaço de Fock dos estados hadrônicos num modelo de quarks, uma mudança de representação é implementada de tal maneira que os hádrons sejam descritos por operadores de campo de partículas elementares. A aplicação da transformação unitária ao Hamiltoniano microscópico de quarks dá origem a Hamiltonianos efetivos que descrevem interações quark-quark, hádron-hádron, e hádron-quark. Hamiltonianos bariônicos efetivos foram derivados no contexto de um modelo de quarks constituintes. Em particular, um potencial efetivo NN foi obtido, deslocamentos de fase singletos de spin foram calculados para este potencial e comparados aos deslocamentos de fase gerados pela troca de mésons 'ômega' do potencial de Bonn
Abstract: The field theoretic Fock-Tani formalism, originally developed in atomic physics to deal with systems where the internal degrees of freedom of atoms cannot be neglected, is generalized to composite hadronic systems. Starting from the Fock space representation of hadron bound states in a quark model, a change of representation is implemented by a unitary transformation such that the composite hadrons are redescribed by elementary-particle field operators. Application of the unitary transformation to the microscopic quark Hamiltonian gives rise to effective Hamiltonians that describe quark-quark, hadron-hadron, and quark-quark interactions. Effective baryon Hamiltonians are derived in the context of a constituent quark model. In particular, an efective NN Fock-Tani potential was obtained, spin-singlet phase shifts were calculated for this potential and compared with the ones generated by the 'ômega' exchange of the Bonn potential
Doutor
15
Mauser, Marcus. „Polarisationseffekte in semileptonischen Zerfällen schwerer Quarks“. [S.l. : s.n.], 2001. http://ArchiMeD.uni-mainz.de/pub/2001/0051/diss.pdf.
16
Jain, Ambar. „Heavy quarks in effective field theories“. Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53228.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 279-290).
Heavy quark physics serves as a probe to understand QCD, measure standard model parameters, and look for signs of new physics. We study several aspects of heavy quark systems in an effective field theory framework, including both phenomenological and formal applications. Phenomenological applications include the leading calculation of penguin amplitudes in charmless non-leptonic B-decays to light mesons, including power suppressed effects that are numerically enhanced by the chiral condensate. We compare our determination of the penguin amplitudes with the experimental results. Also, we calculate the heavy quark jet function at two loops, which is an important ingredient for the next-to-next-to-leading-log invariant-mass distribution of jets induced by tt pair production at a future linear collider. Formal applications include: a definition of top mass relevant for measurements that use top induced jets, a new renormalization group equation in an infrared scale intrinsic to heavy quark masses and its generalization for QCD matrix elements, a threshold mass definition which smoothly connects to the MS mass, and a new method to analyze renormalons in the operator product expansion.
by Ambar Jain.
Ph.D.
17
Enström, Daniel. „Aspects of quarks in exotic matter“. Licentiate thesis, Luleå tekniska universitet, 1999. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16915.
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In this licentiate thesis, two different aspects of particle physics have been studied. The results are presented in four papers. In papers I and II, a model for a joint origin of gamma-ray bursts and dark matter is presented. The common denominator is the deconfined state of quarks, the Quark-Gluon Plasma (QGP). We propose that such quark objects surviving the quark-hadron transition in the early universe, constitute the dark matter and that mergers of these objects are the inner engine of gamma-ray bursts. We have computed stability criteria for macroscopic quark objects, as well as the merger frequency assuming a lognormal distribution in size. In paper III, the helicity amplitudes for rare-meson production invirtual gamma-gamma collisions are computed. We show that it is possible to apply a generalised version of the Brodsky-Lepage scheme for exclusive processes in QCD, when computing these amplitudes. In paper IV, we analyse consequences of the new supernova data, suggesting a non-zero vacuum energy density in the universe. We calculate the intrinsic luminosity correction for high-redshift objects such as gamma-ray bursts and quasars. Two different extensions of the Friedmann-Robertson-Walker universe are used; a non-zero cosmological constant and a time-dependent spatially inhomogeneous energy density component (so-called quintessence). The results show a correction of up to 30% for the conventionally computed luminosities.Godkänd; 1999; 20070321 (ysko)
18
Geng, Chaqiang. „Composite models of quarks and leptons“. Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/76097.
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We review the various constraints on composite models of quarks and leptons. Some dynamical mechanisms for chiral symmetry breaking in chiral preon models are discussed. We have constructed several "realistic candidate" chiral preon models satisfying complementarity between the Higgs and confining phases. The models predict three to four generations of ordinary quarks and leptons.Ph. D.
19
Boyd, Graham John. „Quarks and hadrons on the lattice“. Master's thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/15902.
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Bibliography: p. 159-166.There is a short introduction to the ideas of lattice theory, followed by an equally brief look at pure gauge QCD on the lattice. More details for either of these may be found in the references cited in each section, as well as in [143]. The bulk of this work deals with the problems encountered in placing fermions on to the lattice, and the techniques used for this purpose. The Nielsen-Ninomiya theorem is introduced, with a detailed treatment thereof relegated to an appendix. The two main fermion techniques, due to Wilson (1974); and Kogut and Susskind (1975) are dealt with in some detail. This is followed by a discussion of the construction of hadrons on the lattice, using either Wilson or Kogut-Susskind fermions. There is a chapter covering the algorithms used in numerical simulations of lattice QCD, with some examples illustrating them. The thesis concludes with a discussion of the results obtained thus far on the hadron spectrum, in both the quenched approximation as well as those obtained using dynamical quarks.
20
Agudelo, David Felipe Tamayo. „Materia de quarks a temperatura finita“. reponame:Repositório Institucional da UFSC, 2013. https://repositorio.ufsc.br/handle/123456789/106802.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2013Made available in DSpace on 2013-12-05T22:23:58Z (GMT). No. of bitstreams: 1 318335.pdf: 3639601 bytes, checksum: 3015447719eab188881d3532f1267586 (MD5) Previous issue date: 2013
A constitução dos objetos estelares continua sendo fonte de especulação. Varias hipótesis têm sido aventadas com relação a estrutura interna dos pulsares. Uma delas basei-se na conjetura de Bodmer-Witten, de que a altas densidades a matéria mias estável é formada por quarks desconfinados. Nesse caso, os pulsares seriam estrelas quarkiônicas, constituídas somente de quarks e léptons.O modelos mais comumente usado para descrever matéria de quarks é o modelo de sacola de MIT. Outro modelo, um pouco mais sofisticado é modelo dependente da densidade ou Quark mass density dependent model. Neste trabalho pretendemos comparar as equações de estado desses dois modelos, tanto a temperatura zero, como a temperatura finita. Essas equações de estado servem de input para as equações de Tlman-Oppenheimer-Volkoff (TOV), que são equações da relatividade geral para objetos homogéneos e de simetría esférica. Os resultados obtidos são os valores para massas e raios das estrelas.
21
Moniez, Marc. „Recherche du quark top auprès du détecteur UA2 au collisionneur proton-antiproton du CERN“. Paris 11, 1988. http://www.theses.fr/1988PA112214.
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Cette thèse expose les résultats de la recherche du quark top à l'expérience UA2 du CERN, dans les collisions proton-antiproton aux énergies de 546 GeV et 630 GeV dans le centre de masse, pour une luminosité intégrée de 894 nb-1. Un signal provenant de la désintégration semi-leptonique du quark top (t donne b +électron+ neutrino) a été recherché dans les ensembles d'événements qui contiennent un électron identifié dans l'appareillage et 0,1 ou 2 jets. L'étude détaillée des bruits de fond expérimentaux dus à une mauvaise identification des électrons a été menée ; de même, les sources connues d'électrons réels ont été évaluées à l'aide d'un programme de simulation. Compte tenu de ces études et de la simulation de la production de quark top, une analyse statistique des événements avec 1 électron et 2 jets a permis une discussion sur l'établissement d'une limite inférieure pela masse du quark top. Une limite supérieure sur la production de quark top par le processus (proton-antiproton donne top-antitop) est donnée en fonction de la masse du top. L'extrapolation des études de bruits de fond et de production est développée pour l'expérience UA2' et il est estimé que cette expérience sera en mesure de découvrir le quark top si sa masse est inférieure à 70 GeVfc2.
22
Chan, Ying-kit. „Strange star cooling“. Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B3138254X.
23
Chan, Ying-kit, und 陳英傑. „Strange star cooling“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B3138254X.
24
Veiga, J. S. [UNESP]. „Propriedades da matéria nuclear em modelos de quarks constituintes“. Universidade Estadual Paulista (UNESP), 1996. http://hdl.handle.net/11449/132865.
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Lees, Jean-Pierre. „Recherche du quark Top dans l'expérience UA1 par l'étude des événements contenant un électron isolé de grande impulsion transverse accompagné de jets“. Chambéry, 1987. http://www.theses.fr/1987CHAMS003.
26
Strandberg, Jonas. „Top Quarks at the Tevatron : Measurements of the Top Quark Production and Decay with the D0 Experiment“. Doctoral thesis, Stockholm University, Department of Physics, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-879.
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This thesis presents two measurements of the top quark using 230 pb-1 of data taken with the D0 detector at the Tevatron accelerator. The first measurement determines the top pair production cross section at sqrt(s)=1.96 TeV in proton-antiproton collisions. In the standard model of particle physics the top quark decays almost exclusively into a W boson and a b quark. Candidate events are selected by requiring that at least one jet in the event is tagged with the secondary vertex algorithm. The measured top pair production cross section is:
8.6 +1.6-1.5 (stat. + syst.) +- 0.6 (lumi.) pb.
The second measurement uses the observed and predicted number of events with 0, 1 and 2 b-tagged jets to estimate the ratio R:
R = B(t->Wb) / B(t->Wq)
where q stands for any down-type quark. The measured value is
R = 1.03 +0.19-0.17 (stat. + syst.)
in good agreement with the standard model prediction of R=1. The result can be used to obtain a lower limit for R:
R > 0.61 (95% C.L.).
27
Strandberg, Jonas. „Top quarks at the Tevatron : measurements of the top quark production and decay with the DØ Experiment /“. Stockholm : Dept. of Physics, Stockholm university, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-879.
28
Isert, Dagmar Sigrun. „Transport theory for scalar quarks and gluons“. [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=961877200.
29
Webster, Stephen James. „Improved Monte Carlo simulations of massive quarks“. Thesis, Durham University, 2019. http://etheses.dur.ac.uk/12954/.
Annotation:
Motivated by the interest in top and bottom quark production processes at the LHC, we study the simulation of heavy quarks in the Herwig 7 Monte Carlo event generator. We first present a much improved treatment of heavy quarks in the dipole shower in Herwig 7 and extend the shower to handle decays of massive coloured particles. Taking advantage of these developments, we perform an in-depth study of the simulation of top quark pair production at the LHC, paying particular attention to the parton shower and matching uncertainties involved. Next we implement an algorithm in the dipole shower to include spin correlation effects. Using this algorithm we can produce accurate predictions of the angular distributions of top quark decay products in top pair production at the LHC. Following this we describe a modified version of the veto algorithm used in parton showers that enables the incorporation of weights. We show that the algorithm can be used to significantly reduce the CPU time required to evaluate the effects of scale variations in parton showers. Finally, we investigate the description of gluon splittings to heavy quark pairs in the angular-ordered and dipole parton showers in Herwig 7. While both parton showers correctly reproduce the leading-logarithmic term in the description of these splittings, we find that the effects of subleading contributions are significant.
30
Martins, Mauro Sebastião. „História das partículas: de elétrons aos quarks“. Pontifícia Universidade Católica de São Paulo, 2008. https://tede2.pucsp.br/handle/handle/13384.
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Previous issue date: 2008-05-13This Work, a thesis in history of subatomic particles, is an historic and epistemological development study of the theoretical and experimental subatomic particles and antiparticles from the early Dirac s quantum theory of the electron, published in a year of 1928, until the publications of the theories of the quarks in a decade of the sixths, the Gell Mann theory of quarks include. That research studies was made in primaries and secondary bibliographies, didactic manuals, articles of scientific journals and scientific magazines, history and philosophy of science books and history of particles books. This studies show that in the delimitated period of study, the paradigmatic theories and experiments appear in the period call of common science, in suite the scientific period is the crisis, so, have a concurrency theories and experimental models period, finally appear a paradigmatic theory and experimental model, like the Khun historical analyses. The paradigmatic particles theories and experimental models, appear a manner of broke up whit of old scientific know, like understood of Bachelard analysis. In the daily period the candidate of paradigmatic theory of particles is the supercordas theory. However, ours studies are conclusive that it have a periodic cycle, into theirs, appear the paradigmatic theoretical and experimental models and had surpassed in the suite period by others paradigmatic theoretical and experimental models, and other periodic cycle occur when of paradigmatic theories and experimental models appear, and so on
Este trabalho, uma tese em história das partículas subatômicas, é um estudo da evolução histórica e epistemológica das teorias e experimentos em partículas e antipartículas, desde o advento da teoria quântica do elétron de Dirac, no ano de 1928, até as publicações das teorias sobre os quarks da década de sessenta, incluindo, nestas, a teoria dos quarks de Gell Mann. Os estudos foram embasados nos levantamentos de bibliografias primárias e secundárias: manuais didáticos, artigos de revistas e jornais científicos, obras em história e filosofia da ciência e em história das partículas. Ele demonstra que o período delimitado para o estudo revela que as teorias e experimentos paradigmáticos surgem após um período de ciência normal, seguido de crise e concorrência entre as teorias e modelos experimentais, como compreendido pela análise histórica de Thomas Khun. As teorias e experimentos paradigmáticos, em partículas, surgem de rupturas com o velho conhecimento estabelecido, como entendido pela análise epistemológica de Bachelard, do desenvolvimento do conhecimento científico. No período atual a candidata à teoria paradigmática em partículas, segundo a manifestação da comunidade científica dos pesquisadores em física de partículas, é a teoria das supercordas. Entretanto, os estudos são conclusivos, quanto à existência de ciclos periódicos, nos quais, as teorias e modelos paradigmáticos aparecem e são superados por outras teorias e modelos paradigmáticos emergentes
31
Prager, Hugo. „Phenomenology of extra quarks at the LHC“. Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/424495/.
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In this thesis, we study in a model independent way models of new Physics featuring extra quarks (XQs). These quarks are predicted by several extensions of the Standard Model (SM) but have never been observed yet even though many searches have been designed to find them at the Large Hadron Collider (LHC). After an introduction about the SM and the LHC, we present the main properties of these XQs and a model independent parametrisation that can be used to describe their phenomenology with generic hypotheses about their mixing with SM quarks, both in the case of XQ coupling with SM bosons and with Dark Matter (DM) candidates. In these two cases we study the offshellness effects in pair-production and decay and show that if the Narrow-Width Approximation (NWA), that we describe in detail, is a good approximation of the full result in the small width over mass ratio limit, sizeable differences occur when the XQ width becomes larger. The conclusion of our analysis is that even though the small width assumption is always conservative it is not possible to trivially rescale the mass bounds obtained considering processes of pair production and decay in the NWA to determine constraints for XQs with large widths. We also study the role of interference in the process of pair production of new heavy XQs decaying to SM particles and show that in the NWA the interference contribution can be described by considering a parameter which contains only the relevant couplings and the scalar part of the propagators of the new quarks, both at the cross section level and at the distribution level. Finally, we study how various Supersymmetry (SUSY) searches perform for our simplified model with XQs decaying to DM. We show that cross section upper limit maps and efficiency maps obtained for stop simplified models in stop searches can also be applied to analogous XQ models, provided the NWA applies: the bound for XQs can therefore be obtained from the SUSY ones just by rescaling the exclusion with the XQ cross section.
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GIRLANDA, LUCA. „Signature experimentale de la condensation de quarks“. Paris 11, 1999. http://www.theses.fr/1999PA112258.
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Cette these est dediee a l'etude du mecanisme de la brisure spontanee de la symetrie chirale en qcd. En particulier on a voulu mettre en evidence le role du parametre d'ordre le plus simple, le condensat de quarks <$$q>. Apres avoir decrit differents scenarios possibles de la structure en phases du vide de la qcd, comme fonction du nombre de saveurs de masse nulle n f et de couleurs n c, nous nous sommes concentres sur le cas n f = 2. Afin d'inspecter systematiquement la sensibilite des processus physiques a la valeur du condensat <$$att$$q>, nous avons construit et renormalise, a l'ordre d'une boucle, la version generalisee de la theorie des perturbations chirale, dans le cas de symetrie su(2)su(2). Les applications phenomenologiques etudiees incluent la diffusion a basse energie, les desintegrations 3 + $$att$$ et les desintegrations inclusives non-etranges du lepton. Nous avons illustre comment determiner <$$att$$q> a partir de donnees de haute precision qui sont attendues, dans le domaine de la diffusion , par les experience e865 a bnl, kloe a dane et dirac au cern, et dans le domaine des desintegrations du lepton par les nouvelles usine a b de haute luminosite (babar, cleoiii-cesr).
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Al, Mamun Md Abdullah. „Nuclei, Nucleons and Quarks in Astrophysical Phenomena“. Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1563991151449461.
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Lasry, Nathaniel. „Mélange des quarks : une nouvelle approche géométrique /“. Thèse, Montréal : Trois-Rivières : Université du Québec à Montréal, Université du Québec à Trois-Rivières, 2000. http://www.uqtr.ca/biblio/notice/resume/03-2224587R.html.
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Mémoire (M.Sc.)--Université du Québec à Montréal, 2000.En tête du titre: Université du Québec à Montréal. "Mémoire présenté à l'Université du Québec à Trois-Rivières comme exigence partielle de la maîtrise en physique offerte par extension à l'Université du Québec à Montréal en vertu d'un protocole d'entente avec l'Université du Québec à Trois-Rivières". CaQTU CaQTU Bibliogr. : f. 74.
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Garcia, André Felipe. „Transição quiral na matéria de quarks magnetizada“. Florianópolis, 2012. http://repositorio.ufsc.br/xmlui/handle/123456789/100419.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em FísicaMade available in DSpace on 2013-06-25T19:00:58Z (GMT). No. of bitstreams: 1 311322.pdf: 5230146 bytes, checksum: 30f7940fb6addda231c03960c74fb1ca (MD5)
A física de altas energias é um dos campos de pesquisa mais interessantes da física e de maior atividade atualmente, abrangendo fenômenos físicos que vão desde cosmologia até a física de partículas elementares. Nesta última, sua atuação se dá principalmente nos modernos aceleradores de partículas, como o Relativistic Heavy Ion Collider (RHIC) e o Large Hadron Collider (LHC), onde feixes de partículas colidem entre si produzindo inúmeras outras partículas. A Cromodinâmica Quântica é a teoria que descreve a força nuclear forte entre quarks e glúons, que são os formadores dos hádrons e estão confinados no interior dos mesmos. Entretanto, existe a possibilidade de que em regimes de altas energias caracterizados por temperaturas e/ou densidades elevadas estes quarks e glúons passem da fase hadrônica para uma fase desconfinada representada pelo plasma de quarks e glúons. Essa transição de fase tem inúmeras implicações experimentais (algumas delas sendo atualmente testadas no RHIC e no LHC), além de ser importante na descrição dos estágios iniciais do universo e da matéria que compõe as estrelas de nêutrons. Além disso, recentemente tem-se argumentado que espectadores (partículas periféricas que não se envolvem diretamente na colisão) em colisões não centrais de íons pesados podem gerar fortes campos magnéticos na região de colisão, o que pode influênciar as características da transição de fase. No entanto, devido as dificuldades técnicas em se trabalhar diretamente com a QCD, o uso de modelos efetivos que apresentam algumas propriedades e simetrias desta teoria tem crescido significativamente, mostrando-se uma boa alternativa para contornar estas dificuldades. Um dos modelos mais conhecidos é o modelo de Nambu--Jona-Lasinio (NJL), que, na sua versão mais simples, trata a interação entre quarks up e down como sendo pontual, isto é, sem a participação de gluons. Isto facilita em muito os cálculos envolvidos, apesar de restringir o uso do modelo a escalas de energia que sejam compatíveis com esta aproximação. Nesta dissertação faremos uso da versão SU(2) do modelo de NJL em temperaturas e densidades finitas para estudar a transição quiral na matéria de quarks com e sem a influência de um campo magnético externo. Estudaremos com maiores detalhes o diagrama de fases associado ao modelo, em especial a região da transição de primeira ordem onde há coexistência de fases. Veremos como o campo magnético altera a temperatura pseudo-crítica no crossover, o potencial químico de coexistência em baixas temperaturas e a localização do ponto crítico no diagrama de fases. Até o momento a maioria dos trabalhos relacionados com este tema estão restritos ao estudo dos efeitos do campo magnético no plano $T-\mu$. Neste trabalho damos um passo a frente, investigando também os efeitos do campo magnético sobre algumas grandezas termodinâmicas como a pressão, entropia, densidade bariônica, densidade de energia, susceptibilidade do número de quarks, anomalia do traço e curvas isentrópicas. Um dos resultados mais interessantes da dissertação é uma inesperada "deformação" no diagrama de coexistência de fases no plano $T-\rho$ devido às oscilações na curva de coexistência causadas pelo campo magnético. Este comportamento pode ser entendido em termos do preenchimento dos níveis de Landau em temperaturas baixas.
High energy physics is one of the most interesting research fields of physics in activity nowadays, covering physical phenomena from cosmology to elementary particle physics. Within the latter, high energy physics is present in modern particle accelerators such as the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), where particle beams collide producing several other particles. Quantum Chromodynamics (QCD) is the theory that describes the strong nuclear force among quarks and gluons, which form the hadrons and are confined in their interior. However, there is the possibility that in high energy regimes characterized by high temperatures and/or densities these quarks and gluons undergo a phase transition, changing from the hadronic phase to a deconfined phase represented by the quarkgluon plasma. This phase transition has several experimental implications (some of them being tested in the RHIC and in the LHC), being also important in the description of the early stages of the universe and in the study of the matter in neutron stars. Furthermore, it has been argued in recent years that spectators (particles at the edge of the beam that do not get involved directly in the collision) in non-central heavy ion collision are responsible for creating a strong magnetic field that could affect the features of the phase transitions. However, due to tecnical difficulties in dealing with QCD, the use of less fundamental theories that mimic some of the properties and symmetries of the original theory has growth significantly, being a good alternative to face those difficulties. One of the most popular models is the Nambu{Jona-Lasinio (NJL) model, which, in its simplest version, treats the interaction between up and down quarks as being pontual, with no gluon exchange. This makes calculations a lot easier to perform, but restricts the use of the model to energy scales onsistent with this approximation. In this dissertation we make use of the SU(2) NJL model at finite temperatures and densities in order to study the chiral transition in quark matter under the influence or not of an external magnetic field. We study the phase diagram of the model in detail, paying special attention to the first order transition, where the symmetric and non symmetric phases can coexist. We investigate how the magnetic field affects the crossover pseudocritical temperature, the coexisting chemical potential at low temperatures and the location of the critical end point in the phase diagram. So far, most of the works related to this theme are restricted to the investigation of the magnetic field over the T - u plane only. We take a step forward in this direction, investigating the effects of the magnetic field over some thermodynamic quantities such as the pressure, entropy, baryonic density, energy density, quark number susceptibility, trace anomaly and the isentropic curves or adiabats. One of the most interesting results of this work is the \deformation" of the coexistence phase diagram in the T - u plane caused by the oscillations of the coexistence curve due to the magnetic field. This behavior may be explained in terms of the filing of the Landau levels at low temperatures.
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Paulo, Júnior Ademar. „Interações efetivas entre quarks a baixas energias a partir da Cromodinâmica Quântica considerando o condensado de quark-antiquark“. Universidade Federal de Goiás, 2014. http://repositorio.bc.ufg.br/tede/handle/tede/3064.
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The Quantum Chromodynamics (QCD) is the current theory that aim to describe the strong interactions in the Standard Model. It is a non-abelian gauge theory where quarks and gluons are the fundamental particles. However, QCD exhibits difficulties when low energy regimes are considered and perturbative methods cannot be employed. Thus, effective models are extremely important and useful when low energy limits are considered. Starting with QCD we develop an effetive model taking into account the second order gluon condensate, ⟨Aa A a ⟩, and quark-antiquark, ⟨ qq⟩. The coupled GAP equations are derived for Ns = 3 and numerical solutions are found for that. Furthermore, a functional expansion from effective potencial to the sixth order is calculated and contributions from that terms inserted into the effective lagrangian.
A Cromodin^amica Qu^antica (QCD) e a atual teoria que busca descrever as intera c~oes fortes dentro do modelo padr~ao. Trata-se de uma teoria de calibre n~ao-abeliana em que os quarks e gl uons constituem as part culas fundamentais. Entretanto, a QCD apresenta di - culdades quando consideram-se regimes de baixas energias em que t ecnicas n~ao perturbativas devem ser utilizadas. Assim, o uso de modelos efetivos e de extrema import^ancia e utilidade para os regimes de baixas energias que s~ao os de interesse deste trabalho. Partindo da QCD desenvolveremos um modelo efetivo para intera c~oes entre quarks levando em conta a presen ca dos condensados de gl uons de ordem dois, ⟨Aa A a ⟩, e de quark-antiquark, ⟨ qq⟩. As equa c~oes do GAP acopladas s~ao obtidas para Ns = 3 e suas solu c~oes num ericas s~ao encontradas. Al em disso, a expans~ao funcional do potencial efetivo at e sexta ordem no campo dos quarks e calculada e as contribui c~oes destes termos consideradas na lagrangeana efetiva.
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Gil, Jhon Andersson Rosero. „Decaimento eletrofraco da matéria de quarks no interior das estrelas de nêutrons“. reponame:Repositório Institucional da UFABC, 2014.
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Orientador: Prof. Dr. Germán LugonesDissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2014.
Neste trabalho, estudamos a transicao de fase de materia hadronica a materia quarks em estrelas de neutrons e proto-estrelas de neutrons. A transicao comeca com o deconfinamento dos hadrons, que e governado pelas interacoes fortes, e e seguido pelo decaimento fraco dos quarks ate que a materia de quarks atinge o equilibrio quimico. Calculamos a taxa de todos os processos de interacao fraca relevantes na materia quarks quente e densa e resolvemos a equacao de Boltzmann, a fim de obter a escala de tempo de decaimento e a emissividade de neutrinos. Na equacao de estado, analisamos sistematicamente o efeito das interacoes fortes perturbativamente ate primeira ordem em ¿¿c, e o efeito datemperatura finita e massa do quark estranho. Nossos resultados mostram que a transicao aumenta a temperatura da materia quarks ate 60.70 MeV e o equilibrio quimico e atingido em uma escala de tempo de um nanossegundo. A emissividade de neutrinos por barion e muito grande, o que leva a emissao de uma energia por barion de 10.60 MeV sob a forma de neutrinos. Finalmente, analisamos as consequencias astrofisicas dos resultados.
Thermodynamics allows us to analyze the performance of thermal machines, which has the ability to convert the heat into useful work. Among others, the laws of thermodynamics (especially the second) impose limits in various processes including information processing in classical computers. The development of increasingly smaller computing devices, has raised questions about which would limit the applicability of the laws of thermodynamics, when they are close to the quantum limit. This type of questioning has linked different disciplines into a new area of research that has been called quantum thermodynamics. This dissertation is inserted into this new field of knowledge. Specifically we study the possibility of implementing a quantum heat engine which operates out of equilibrium, and employs a single "qubit" as working substance. For this purpose we use the underlying tools of fluctuations theorems to adequately express quantities such as work and heat (which in the quantum context are stochastic variables). We describe in detail the thermodynamic cycle for work extraction in finite time, whose dynamics is controlled by "quenches", or sudden changes in an external field. The proposed protocol can be implemented and fully characterized using the current technology in the context of " Nuclear Magnetic Resonance (NMR)". Finally, we show the regimes of the machine operation
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Samways, Benjamin. „A lattice measurement of the B*Bπ coupling using DWF light quarks and the relativistic heavy quark action“. Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/361526/.
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I describe a calculation of the B*Bπ coupling in lattice QCD. The B*Bπ coupling is directly related to gb, the leading order low-energy interaction constant of heavy meson chiral perturbation theory. Knowledge of the coupling will help decrease systematic uncertainties in lattice QCD B-physics studies, which are important to constrain the CKM matrix and probe the Standard Model. This calculation is performed with 2+1 flavours of dynamic quarks using the domain wall fermion action. To simulate the heavy b-quark I use a non-perturbatively tuned relativistic heavy quark action which keeps discretisation effects under good control. This allows me to make the first calculation of the B*Bπ coupling directly at the physical b-quark mass. I conduct a chiral and continuum extrapolation to the physical point and consider all sources of systematic error. The final result including both statistical and sytematic errors is gb = 0.567(52)stat(58)sys.
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Gimenez, Diógenes Domenicis. „Estudo da coincidência elétron-jato em colisões próton-próton e próton-núcleo no experimento ALICE“. Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-13032018-134433/.
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Esta tese apresenta um estudo inédito da distribuição de jatos correlacionados com elétrons provenientes de decaimentos de quarks pesados (HFe), reconstruídos e selecionados com o ALICE (A Large Ion Collider Experiment, em inglês). Os observáveis foram medidos em colisões pp com energia do centro de massa s = 8 TeV e em colisões p-Pb a sNN = 5.02 TeV, no LHC (Large Hadron Collider, em inglês). Estudar os quarks pesados formados durante as colisões relativísticas entre íons pesados é uma importante maneira para estudar o meio formado, conhecido como QGP (Quark Gluon Plasma, em inlgês). Isso se deve ao fato de que eles são criados no início da colisão e, portanto, interagem com o QGP durante toda sua existência. Em seguida, tais quarks fragmentam em mésons que podem decair, via canal semi-leptônico, em elétrons (e pósitrons). Esses léptons podem ser utilizados para indicar a existência de um quark pesado e permitir o estudo do QGP. Os processos de espalhamento duro, fragmentação e decaimento dão origem a diversas partículas que estão colimadas em uma região espacial, a que chamam jato. A reconstrução e o estudo de jatos têm sido usados para extrair mais informações do meio. Os elétrons foram selecionados pelo TPC (Time Projection Chamber, em inglês) e pelo EMCal (Electromagnetic Calorimeter, em inglês). O método de massa invariante foi utilizado para excluir elétrons não provenientes do decaimento de quarks pesados. Os jatos foram reconstruídos com o auxílio das bibliotecas do Fastjet, algorítmo anti kT e R = 0.4. A seleção de pares HFe-jato pode permitir uma melhor compreensão das propriedades do QGP e de sua interação com quarks pesados. Foram obtidos, para pp e p-Pb, os espectros de momento pT,chjet do jato, em dois intervalos de distância angular entre o elétron e o jato: regiões em oposição (away) e colinear (near). Também foi obtida a distribuição da distância angular para diferentes intervalos de momento peT do elétron. Os resultados para pp e p-Pb foram comparados através de dois observáveis: um em função do momento pT,chjet do jato, e outro em função do momento peT do elétron. O primeiro consistiu na razão dos espectros de momento pT,chjet do jato em pp e em p-Pb. O segundo, na razão do valores obtidos em pp e em p-Pb das áreas dos picos de cada uma das duas regiões de . Em ambos os casos, os valores das razões são compatíveis com a unidade, o que indica que a inexistência de efeitos extras em p-Pb em relação a pp.This thesis presents the first measurement of the distribution of jets that are correlated to heavy-flavour decay electron (HFe), reconstructed and identified with ALICE (A Large Ion Collider Experiment). The observables were measured in pp collisions at center of mass energy s = 8 TeV and in p-Pb at sNN = 5.02 TeV at the Large Hadron Collider (LHC). Exploring the heavy quarks created in relativistic heavy ion collisions is a powerful approach to study the new formed medium, known as Quark Gluon Plasma (QGP). This is due to the fact that they are created in the beginning of the collision, via hard scattering, and interact with the QGP throughout its whole existence. These quarks fragment into mesons that can decay (via the semi-electronic channel) into electrons (and positrons). These leptons can be used to identify the creation of a heavy quarks and allow QGP studies. The hard scattering, fragmenting and decaying processes originate several particles that are collimated in a conical region, and they can be grouped in what is called jet. The reconstruction and study of jets has been used to retrieve more information about the QGP and it is also a useful probe. The selected electrons were identified by the Time Projection Chamber (TPC) and the Electromagnetic Calorimeter (EMCal). Heavy-flavour decay electrons were selected via invariant mass method. The jets were reconstructed by the Fastjet framework, with the algorithm anti kT and R = 0.4. The HFe-jet pairs selection may allow a better comprehension of the QGP properties and its interactions with the heavy quarks. A jet pT,chjet spectrum was obtained, for pp and p-Pb, in two intervals of angular distance between the jet and the electron: away and near sides. The angular distance distribution was also obtained in different electron peT intervals. The results for pp and p-Pb were compared through two observables: the first one as a function of the jet pT,chjet, and the second, as a function of electron peT. The former consists in calculating the ratio of the jet pT,chjet spectra, in pp and in p-Pb. The latter, consists in calculating the ratio of the areas, in pp and in p-Pb, of each peak in the distribution. Both were compatible with the unity, which indicates that there is no extra effect in p-Pb with respect to pp.
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Harko, Tiberiu. „Properties of strange stars“. Thesis, Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk:8888/cgi-bin/hkuto%5Ftoc%5Fpdf?B23242280.
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Roy, Christelle. „L'Etrangeté du Plasma de Quarks et de Gluons“. Habilitation à diriger des recherches, Université de Nantes, 2005. http://tel.archives-ouvertes.fr/tel-00011076.
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A l'instar des trois autres expériences auprès du collisionneur RHIC (Relativistic Heavy Ion Collider) du Brookhaven National Laboratory près de New York, STAR (Solenoidal Tracker At RHIC) est entièrement consacrée à la mise en évidence de cet état particulier de la matière nucléaire prédit par les calculs de QCD (Quantum ChromoDynamics) sur réseau : le plasma de quarks et de gluons (QGP pour Quark Gluon Plasma). Cet état, supposé être celui de l'Univers quelques fractions de secondes après le Big Bang, consisterait d'après sa définition originelle de 1975, en une matière dans laquelle quarks et gluons seraient déconfinés, sans interaction. Il pourrait être créé en laboratoire lors de collisions d'ions lourds réalisées à des énergies ultra-relativistes afin d'atteindre des températures et densités d'énergie extrêmes.Après quasiment 20 ans de recherche auprès des différents accélérateurs de particules américains et européens, le CERN annonce le 10 février 2000 au cours d'une conférence de presse, la mise en évidence expérimentale d'un état particulier de la matière nucléaire, compatible avec la formation d'un QGP, sans pouvoir toutefois le caractériser pleinement. Les expériences du RHIC ont alors pris le relais. Aujourd'hui, au travers une pléthore de résultats nouveaux et parfois bien surprenants, il apparaît de façon de plus en plus certaine, qu'effectivement un état atypique de matière nucléaire a été créé à RHIC et notre vision du QGP comme un gaz parfait de partons n'interagissant que très faiblement, a depuis changé. Un nouvel acronyme a été défini : sQGP pour Strongly Interacting QGP.
Pour parvenir à cette observation, il a fallu passer par la caractérisation même de l'évolution des collisions d'ions lourds, du point de vue chimique et dynamique, en comparant les phénomènes des collisions d'ions lourds pour lesquelles les conditions devraient être réunies pour former un QGP à des collisions d'énergies moindres ou de systèmes plus légers qui ne peuvent permettre cette formation. Le QGP est en effet produit de manière beaucoup trop furtive pour pouvoir le sonder directement. Mon mémoire d'Habilitation à Diriger des Recherches présente les résultats des analyses que j'ai menées et qui ont contribué à la mise en évidence de la formation d'un état nouveau au RHIC et à cette nouvelle vision du plasma. Les stigmates du QGP ont été recherchés avec les particules contenant des quarks étranges : les résonances de particules simplement étranges et les baryons doublement étranges.
La production des résonances étranges Lambda(1520) apporte en effet des informations sur la phase d'hadronisation du plasma (lorsque les partons se recomposent en hadrons) : selon leur observation ou non, il pourrait être possible de caractériser le freeze-out chimique (instant où les interactions inélastiques cessent et la composition chimique du système est figée), le freeze-out cinétique (instant où les interactions élastiques cessent et les particules n'interagissent plus), si ces deux freeze-out coïncident ou si, au contraire ils sont séparés dans le temps et de combien. L'idée est la suivante : les Lambdas(1520) se désintègrent quasiment instantanément en un proton et un kaon. Par conséquent, si le temps entre les freeze-out chimique et cinétique est long, les produits de désintégration de ces particules peuvent être absorbés dans le milieu dense qui a été créé. En revanche, si les deux freeze-out coïncident ou sont très proches, les produits de désintégration ne sont pas affectés et la particule mère, c'est-à-dire la résonance, peut être identifiée. Ainsi, en mesurant les taux de production de ces particules dans les collisions proton–proton pour lesquelles les deux freeze-out coïncident, et en comparant les taux obtenus dans les collisions Au–Au, à l'énergie nominale du RHIC, il est apparu qu'effectivement, au moins 4 fm/c séparent les deux freeze-out dans les collisions Au–Au. Cette conclusion constitue une étape importante dans la compréhension des collisions d'ions lourds ultra-relativistes et du comportement de la matière dans des conditions extrêmes. Cette analyse est apparue comme originale au sein de la collaboration STAR, étant la première étude sur les résonances étranges. Des algorithmes spécifiques ont dû être mis au point et sont largement utilisés au sein de la collaboration qui depuis étudie de nombreuses autres résonances ou recherche des objets plus exotiques.
La production des baryons étranges a été largement investiguée les années passées car une augmentation « anormale » des taux de production est attendue si un QGP est formé. Les expériences du CERN ont observé effectivement une surproduction de l'étrangeté dans les collisions Pb–Pb mais n'ont pu conclure de manière décisive quant à une formation éventuelle d'un plasma car ces résultats pouvaient être également reproduits par des modèles de gaz de hadrons. Nous avons mené une analyse similaire avec les données de STAR en comparant les taux de production des Xi, baryons doublement étranges, dans les collisions proton–proton et Au–Au à sqrt(s_NN) = 200 GeV. Là aussi, les résultats sont demeurés ambigus. Ainsi, ces résultats ont conduit un certain nombre de physiciens à ne plus considérer les taux de production de particules étranges comme une signature robuste de la formation d'un QGP. En revanche, l'étrangeté est revenue sur le devant de la scène, de façon plus indirecte donnant des informations très diverses et sur les différentes étapes de la collision.
Les Xi ont révélé tout d'abord que le système créé à l'énergie nominale du RHIC serait en équilibre thermique et chimique et que les températures de freeze-out chimique sont proches de la température de déconfinement prédite par QCD. Nous avons également étudié les phénomènes dynamiques collectifs, appelés flot, qui naissent des interactions entre constituants et se traduisent par une émission de matière dans des directions privilégiées de l'espace de phase. En accord avec leurs faibles sections efficaces d'interaction, les Xi semblent émis bien plus tôt que les particules plus légères. Toutefois, le fait que ces baryons subissent un flot important, laisse supposer qu'elles auraient développé un flot, donc qu'elles auraient été soumises à des interactions, avant la phase d'hadronisation, autrement dit, dans une phase partonique. Les partons subiraient donc des interactions résiduelles, contrairement à ce que préconisaient les théoriciens du milieu des années soixante-dix.
Par ailleurs, en 2003, les quatre expériences du RHIC ont révélé conjointement la mise en évidence du phénomène de jet-quenching dans les collisions d'ions lourds : il traduit une diminution de la production de particules chargées de très haute impulsion transverse s'expliquant par la perte d'énergie des partons dans un milieu très dense. Nous avons réalisé cette analyse en considérant les X et montré que non seulement ces baryons subissent un jet-quenching mais aussi qu'ils ont un comportement différent de celui des mésons. Une dépendance des phénomènes dynamiques au type de particules a ainsi été mise en évidence en accord avec les modèles de coalescence préconisant que les hadrons se forment à partir de la recombinaison des quarks. Là aussi, émergence des partons comme degrés de liberté pertinents.
A partir de ces résultats entre autres, certains théoriciens affirment la découverte du QGP à RHIC mais les expérimentateurs sont plus prudents et désirent auparavant confirmer et enrichir leurs résultats par l'étude d'autres observables qui viendraient corroborer ces observations. Ces années ont été particulièrement stimulantes par l'évolution de nos connaissances grâce aux formidables résultats produits par les quatre expériences du RHIC. Les « vielles » signatures ont fait peau neuve se transformant en sondes nouvelles et riches en informations originales. La conception du QGP a évolué : il ne s'agit plus d'un gaz parfait constitué de partons évoluant librement mais d'un sQGP.
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Perret, Pascal. „Tests électrofaibles du Modèle Standard et quarks lourds“. Habilitation à diriger des recherches, Université Blaise Pascal - Clermont-Ferrand II, 2002. http://tel.archives-ouvertes.fr/tel-00001683.
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Andrieux, Vincent. „Polarisation of quarks and gluons inside the nucleon“. Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112244/document.
Annotation:
Cette thèse présente un travail relatif à l'étude de la structure en spin longitudinal du nucléon. Le but est de déterminer la contribution des constituants du proton, quarks et gluons, à la formation de son spin 1/2. L'analyse s'appuie sur les données de l'expérience COMPASS qui bénéficie d'un faisceau de muons polarisés à 200 GeV diffusé sur les protons polarisés d'une cible d'ammoniac (NH₃) de 1,2 m de long. On mesure l'asymétrie de spin longitudinal des sections efficaces de diffusion profondément inélastique. On extrait la fonction de structure en spin du proton, g₁p, étendant la couverture cinématique mondiale à des régions inexplorées jusqu'à maintenant (0,0036 < x < 0,57; 1,03 < Q² (GeV/c)² < 96 et 23 < W² (GeV/c)² < 320). Les résultats, d'une grande précision statistique, sont inclus dans une analyse des données mondiales de g₁p, g₁d et g₁n (proton, deutéron et neutron) au 2ème ordre de QCD afin de paramétrer les distributions de quarks et de gluons polarisés. L'étendue de la couverture cinématique en x et Q² des données mondiales de g₁, un élément déterminant pour la sensibilité à la polarisation des gluons ΔG, s'avère trop limitée pour constituer une extraction précise de celle-Ci. Néanmoins, l'analyse QCD permet de déterminer la contribution du spin des quarks au spin du proton à 0.26<ΔΣ<0.33 à Q² = 3 (GeV/c)² dans le schéma MSbar. L'étude montre que l'incertitude principale sur ΔΣ est liée au choix des formes fonctionnelles utilisées dans la régression des données. Enfin, la règle de somme de Bjorken, qui constitue un test de QCD, est vérifiée avec une précision de 9% en utilisant les données de COMPASS uniquementThe work presented in this thesis is related to the study of the longitudinal spin structure of the nucleon. The aim is to determine the contribution to the spin 1/2 of the proton in terms of its constituents, quarks and gluons. The analysis is performed on the data taken with the COMPASS experiment, which benefits from a polarised muon beam at 200 GeV scattered off polarised protons from an ammonia target of 1.2 m long. The double longitudinal spin asymmetry of deep inelastic scattering cross-Section. The spin-Dependent structure function of the proton g₁p is derived from these measurements, which extend the kinematic world coverage to unexplored region so far (0,0036 < x< 0,57; 1,03 < Q² (GeV/c)² < 96 and 23 < W² (GeV/c)² < 320).The results obtained with a high statistical precision are included in a Next-To-Leading order QCD analysis of world g₁p, g₁d and g₁n (proton, deuteron and neutron) data to parametrise the polarised quark and gluon distributions. The g₁ world coverage of the x and Q² kinematic domain, which is a key point in the sensitivity to the gluon polarisation ΔG, turns out to be too limited for an accurate ΔG determination. Nevertheless, the QCD analysis allows to determine the quark spin contributions to the proton spin to 0.26<ΔΣ<0.33 at Q² = 3 (GeV/c)² in the MSbar scheme. The dominant uncertainty on ΔΣ is related to the choice of functional forms assumed in the fit. Finally, the Bjorken sum rule, which constitutes a fundamental test of QCD, is verified on the COMPASS data alone with a precision of 9%
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Mello, Cedrick Miranda. „Estudo da detecção de quarks top no LHC“. Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-08032013-122617/.
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Este trabalho consistiu em analisar a possibilidade de verificação da violação de sabor em correntes neutras intermediadas por glúons de Kaluza-Klein (GKK) através do modelo de dimensões extras compactas e curvas. Este introduz a possibilidade de violação de sabores em correntes neutras através de processos do tipo próton/próton em top/anti-quark c. Inicialmente estudamos o comportamento de jatos com altos momentos transversos (da ordem de 300 GeV) e suas subestruturas. Após isto, estudamos a detecção do quark top através dos algoritmos HEPTopTagger e Johns Hopkins (fizemos uma breve comparação entre eles). Por último, propusemos duas maneiras de encontrar os GKK. Uma delas, através da procura de somente quarks top. A outra, através da procura de um quark top e um jato sem subestrutura (algoritmo do tipo TJ). Pudemos ver que a possibilidade de encontrar o fenômeno de violação de sabores é acessível (a razão S/B da ordem de 0,1) para ambos os casos de massa analisados através do algoritmo do tipo TJ.This study was to examine the possibility of verifying the violation of flavor in neutral currents mediated by Kaluza-Klein gluons (GKK), in which it was introduced by compact warped extra dimensions. The possibility of violation of flavors in neutral currents occurs through processes like proton/proton into quark top/ antiquark charm. Initially we studied the behavior of jets with high transverse momentum (the order of 300 GeV) and its substructures. After this, we studied the detection of the top quark via HEPTopTagger and Johns Hopkins algorithms (we did a brief comparison between them). Finally, we proposed two ways to find the GKK. One of them, by searching for only quark top. The other, by looking for a quark top and a jet without substructure (algorithm of TJ type). We could see that the possibility of encountering the phenomenon of violation of flavors is accessible (the ratio S/B is the order of 0.1) in both cases of mass analyzed by TJ type algorithm.
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Motta, Théo Ferraz. „Matéria de Quarks fria sob campo magnético forte“. Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-25052017-105222/.
Annotation:
Esta dissertação apresenta uma breve revisão introdutória de alguns aspectos importantes de astrofísica nuclear e da fenomenologia do plasma de quarks e glúons a baixas temperaturas. Acredita-se que tal estado da matéria existe no núcleo de estrelas de nêutron e possivelmente de outros objetos compactos em astrofísica. Uma equação de estado para tal sistema é derivada incluindo as influências dos condensados de glúon e do campo magnético que também é uma característica importante das estrelas de nêutron. Finalmente, essa equação de estado é aplicada para o estudo de estrutura estelar de estrelas compactas e alguns resultados importantes são discutidos.This dissertation presents a brief introductory overview of some key aspects of nuclear astrophysics and of the phenomenology of the quark gluon plasma at cold temperatures which is believed to exist inside the core of neutron stars and possible other compact astrophysical objects. An equation of state for this state of matter is derived incluing the influence of gluon condensates and the magnetic field which is also an important characteristic of neutron stars. And finally this equation of state is applied to the study of compact stellar structure and some important results are discussed.
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Carvalho, Sheyse Martins de. „Efeitos do confinamento na matéria de quarks supercondutora“. Instituto Tecnológico de Aeronáutica, 2010. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=1564.
Annotation:
No regime de altas densidades, os modelos de quarks com geração dinâmica de massa prevêem que a matéria estranha de quarks pode aparecer em duas fases, uma fase quiral simétrica e outra quebrada que não é absolutamente estável. A altas densidades, a abundância dos quarks u, d e s é a mesma na fase quiral simétrica e não há elétrons. Estas duas propriedades também estão presentes numa nova fase supercondutora que deve ocorrer na QCD a altas densidades, conhecida como fase fechada de cor e sabor (CFL). Isto sugere que a matéria estranha a altas densidades possa fazer uma transição para fase CFL, na qual a energia é diminuida pelo emparelhamento BCS dos quarks. Nesta tese fazemos um estudo numa versão completa do modelo cromodielétrico (CDM) onde implementamos o emparelhamento dos quarks e analisamos a fase supercondutora de cor e sabor. Para investigar o efeito do confinamento nesta fase, derivamos uma lagrangeana efetiva para o emparelhamento, expandindo-a em torno do valor do campo médio ? do campo confinante do CDM e em ordem mais baixa. A constante efetiva da interação de emparelhamento depende explicitamente de ?. As equações de gap auto-consistentes no canal escalar e vetorial são obtidas e resolvidas numericamente para diferentes valores dos parâmetros do CDM. Para o potencial quártico usado nos cálculos, na solução quiral, obtida para grandes valores do campo de confinamento e pequenos valores da massa do quark, os quarks não emparelham. Para a solução quiral quebrada, onde ? é pequeno e os quarks são massivos, encontramos emparelhamento. Mostramos que o canal vetor do gap é mais fraco que o escalar, e o gap de emparelhamento vetorial pode chegar até 120 MeV para altas densidades.
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Tran, Huong Lan. „Recherche de quarks lourds avec le détecteur ATLAS“. Paris 7, 2013. http://www.theses.fr/2013PA077274.
Annotation:
Une recherche de quarks lourds est presentée dans cette these. Elle est composée de trois parties principales. Dans la première partie est presentée l'étude du facteur de qualité Q pour les calorimètres à Argon liquide de ATLAS. Le facteur Q est une quantité définie pour estimer l'accord entre le signal mesuré et la prédiction. Dans le cas où la prédiction n'est pas parfaite, il peut induire un rejet de bons signaux. La prédiction peut cependant être corrigée en utilisant des signaux purs d'ionisation selectionnés dans les données. Les résultats montrent une bonne amélioration: La correction de la prédiction a permis de réduire la dépendance du facteur Q avec l'énergie du signal. Les nouvelles prédiction des formes de signal corrigées par les résidus ont été intégrées à la base de données d'ATLAS pour être utilisées lors de futures campagnes de reconstruction des données. La deuxième partie est le coeur de la thèse: le développement d'une analyse de recherche de quarks lourds innovante. Cette analyse est réalisée en trois étapes. Dans la première étape, une méthode de maximum de vraisemblance est utilisée pour déterminer le nombre d'événements de signal éventuellement présent dans les données. Un excès d'environ 2a est observé: Ns= 82 +39. Dans la deuxième étape, la méthode Plot est utilisée pour construire la distribution —36 s de variables de contrôle, par exemple la masse invariante de trois jets. Le résultat donne des distributions compatibles avec l'hypothèse nulle, qui nuance l'excès obtenu. Enfin dans la dernière étape, une méthode statistique a été développée pour combiner l'information des deux premières étapes. La méthode aboutit à un résultat compatible avec celui de l'approche standard adoptée dans ATLAS; il exclut des quarks lourds de mass mt, < 520 GeV/c2 (600 GeV/c2 attendu) à 95 % CL en utilisant 4. 7 fb--, de données à 7 TeV. La dernière partie de cette thèse présente ma contribution au Groupe Exotics sur la recherche de quarks de type vecteur, où j'ai été impliquée dans l'analyse de canal dilepton de même signe; j'ai également contribué la mise en place de la combinaison des differentes analyses. Un quark vecteur de charge +2/3 (-1/3) de mass inférieure à 550 (450) GeV/c2 est exclu quelque soit son rapport d'embranchement en tH, tZ ou bW (bH, bZ, tW)A search for heavy quarks is presented in this thesis. It is organized in three main parts. In the first part presented the study on the quality factor for the liquid Argon calorimeters of ATLAS. The Q-factor is a quantity defined to estimate the agreement between the measured and the predicted pulse shape. In case the prediction is not perfect, it can lead to spurious rejection of good signal. The prediction however can be corrected using a pure sample of signal selected from the data. The results show a clear improvement: correcting the prediction helped to reduce the dependence of the Q-factor on the signal's energy. The new pulse shape predictions have been stored in the ATLAS database to be used in the next data reprocessing. The second part is the heart of the thesis: development of a novel analysis to search for heavy quarks. This novel approach is performed in three steps. In the first step, a Likelihood fit method is built to determine the number of signal events in the data. An excess w. R. T. Expectation in absence of signal events is observed: N = 82+39. In the second step, the Plot method is used to reconstruct distributions S-36 s of control variables, for instance the invariant mass of three jets. The result shows distributions compatible with the null hypothesis. Finally in the last step, a statistical method has been developed to combine the output of the first two steps. The method leads to a result compatible with the standard approach in ATLAS; It excludes heavy quarks with masses mtbelow 520 GeV/c2 (600 GeV/c2 expected) at 95 % CL using 4. 7 fb-i of 7 TeV data. The last part of this thesis presents my contribution to the Exotics Group on the search for vector-like quarks, where I was involved in the same-sign dilepton channel analysis; I also contributed to the combination of various analyses. As a summary, a vector-like quark of charge +2/3 (-1/3) with mass smaller than 550 (450) GeV/c2 is excluded regardless of its branching ratio to tH, tZ or bW (bH,bZ,tW )
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Khamseh, Ava. „Lattice phenomenology of heavy quarks using dynamical fermions“. Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28855.
Annotation:
The Standard Model of particle physics is believed to be only the low energy limit of a more fundamental theory. In order to determine its range of validity, a major part of theoretical and experimental efforts in physics is dedicated to precision tests of the Standard Model. Lattice QCD is a non-perturbative, first-principles approach to Quantum Field Theory. It plays an important role in flavor physics by providing calculations of non-perturbative strong interaction contributions to weak processes involving quarks. Measurements of hadronic quantities can be used to constrain the Standard Model as well as theories Beyond the Standard Model. The first part of this thesis contains theoretical developments regarding non-perturbative renormalization. A new renormalization scheme, RI/mSMOM, for fermion bilinear operators in QCD at non-vanishing quark mass is presented. In order to investigate the properties of the mSMOM scheme, an explicit one-loop computation in perturbation theory using dimensional regularization is performed. Numerically, vertex functions are generated on the lattice, with an appropriate projector, based on the RI/SMOM scheme and the renormalization factors are extracted. Quantities measured include renormalization of the axial current ZA, required to renormalize the axial current entering the computation of the decay constant and the renormalization of the bag parameter. The second part of this report focuses on flavor physics phenomenology on the lattice. It presents results of the first run of the RBC/UKQCD charm project with (2+1)-flavor Domain Wall fermions. Observables and matrix elements are measured on lattices with Iwasaki gauge action. There are two ensembles at the physical point with inverse lattice spacings 1.73 and 2.36 GeV and a third finer ensemble at 2.76 GeV as well as four other auxiliary ensembles with smaller volumes and heavier pion masses which are used to perform the continuum extrapolations. The quantities measured in the region of the charm quark mass are meson masses, decay constants, the matrix element of the OV V +AA operator, the neutral D-meson mixing parameter B and the SU(3) breaking ratio ξ.
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Medina, Tulio Eduardo Restrepo. „Geração radiativa de repulsão vetorial para quarks leves“. reponame:Repositório Institucional da UFSC, 2014. https://repositorio.ufsc.br/xmlui/handle/123456789/129306.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2014Made available in DSpace on 2015-02-05T20:56:09Z (GMT). No. of bitstreams: 1 330269.pdf: 2723044 bytes, checksum: acc5bb1f16ab0d07a08b676e16f1ea63 (MD5) Previous issue date: 2014
Abstract: We apply a non-perturbative analytical method, known as the Optimized PerturbationTheory (OPT), to the Polyakov-Nambu-Jona-Lasinio (PNJL) model in order to investigate physical quantities associated with the QCD phase transitions. We consider the Taylor expansion of the pressure in powers of µ/T obtaining the second cumulant (c2) which is associated to the quark number susceptibility. We discuss how the OPT nite Nc radiative (quantum) corrections induce a contribution to the pressure which behaves as a vector repulsion even when such a channel is absent in the original classical potential. Our results are then compared with the ones furnished by lattice QCD simulations and by the large-Nc approximation showing that, physically, the OPT results resemble those furnished by the latter approximation when a repulsive vector channel is explicitly included in the classical potential. In this case, both approximations fail to correctly describe the Stefan-Boltzmann limit at high temperatures. We discuss how this problem can be circumvented by taking the couplings to be temperature dependent so as to simulate the phenomenon of asymptotic freedom. Since this is the first time the OPT is applied to the PNJL we also discuss many technicalities associated with the evaluation of two loop (exchange) diagrams.
Neste trabalho o método analítico não perturbativo conhecido como Teoria de Perturbação Otimizada (OPT) é aplicada ao modelo de Polyakov-Nambu-Jona-Lasinio (PNJL) para que quantidades físicas, associadas com as transições de fase da QCD, possam ser calculadas. A expansão da pressão em potências de µ/T é considerada para obter o segundo cumulante (c2) que é uma quantidade relacionada com a susceptibilidade do número de quarks. Primeiramente discutimos como as correções radiativas de Nc finito geradas pela OPT produzem uma contribuição que se comporta como um termo vetorial repulsivo mesmo quando este tipo de canal está ausente no potencial clássico original. Em seguida, nossos resultados são comparados com aqueles fornecidos pelas simulações na rede e também pela aproximação de Nc grande(LN). Fisicamente, os resultados da OPT são similares aqueles fornecidos pela aproximação LN quando um canal vetorial repulsivo é explicitamente incluido no potencial clássico. Neste caso, nenhuma destas aproximações analíticas produz corretamente o limite de Stefan Boltzmann para altas temperaturas. Contudo, nossos resultados sugerem como estes problemas podem ser contornados tomando-se as constantes de acoplamento como sendo dependentes da temperatura, de maneira que o fenômeno da liberdade assimptótica possa ser simulado. Esta é a primeira vez que a OPT é aplicada ao modelo de PNJL e por isto vários aspectos técnicos relacionados com o cálculo de diagramas de dois laços são também aqui apresentados.
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Turcotte, Marc Gilles. „Weak decays of charmed particles“. Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72805.