Masses of ground and excited-state hadrons

We present the first Dyson-Schwinger equation calculation of the light hadron spectrum that simultaneously correlates the masses of meson and baryon ground- and excited-states within a single framework. At the core of our analysis is a symmetry-preserving treatment of a vector-vector contact interaction. In comparison with relevant quantities the root-mean-square-relative-error/degree-of freedom is 13%. Notable amongst our results is agreement between the computed baryon masses and the bare masses employed in modern dynamical coupled-channels models of pion-nucleon reactions. Our analysis provides insight into numerous aspects of baryon structure; e.g., relationships between the nucleon and Delta masses and those of the dressed-quark and diquark correlations they contain.Comment: 25 pages, 7 figures, 4 table

Modellierung ultrarelativistischer Schwerionenkollisionen mit der Quark-Molekulardynamik qMD

This thesis presents a model for the dynamical description of deconfined quark matter created in ultra-relativistic heavy ion collisions, treating quarks and antiquarks as classical point particles subject to a colour-dependent, Cornell-type potential interaction. The model provides a dynamical handle for hadronization via the recombination of quarks and antiquarks in colour neutral clusters. Gluons are not included explicitly in the model,but are described in an effective manner by the means of the potential interaction. The model includes four different quark flavours (up, down, strange and charm) and uses current masses for the quarks. The dynamical evolution of a system of colour charges subject to the Hamiltonian equations of motion of the model yields the formation of colour neutral clusters of quarks and antiquarks, which are subject only to a small remaining interaction, the strong interquark potential notwithstanding. These clusters can be mapped onto hadrons and hadronic resonances. Thus, the model allows a dynamical description of quarks degrees of freedom in heavy ion collisions, including a recombination scheme for hadronization. The thermal properties of the model turn pout to be very satisfying. The model shows a transition from a confining phase to a deconfined phase with rising temperature, going hand in hand with a softest point in the equation of state and a rise of energy density and pressure to the Stefan-Boltzmann limit of a gas of quarks and antiquarks. Moreover, the potential interaction is screened in the deconfined phase. For the dynamical description of ultra-relativistic heavy ion collision, the qMD model is coupled to UrQMD as a generator for its initial conditions. In this way, a fully dynamical description of the expansion and hadronization of the fireball created in such collisions can be achieved. Non-equilibrium aspects of the expansion dynamics and hadronization by recombination of quarks and antiquarks are discussed in detail, and a comparison with experimental data of collisions at the CERN-SPS is presented. The big advantage of the qMD model is the possibility to study cluster formation, including exotic clusters, and fluctuations in a dynamical manner. As an example, event-by-event fluctuations in electric charge are studied. Such fluctuations have been proposed as a clear criterion to distinguish a deconfined system from a hadrons gas. However, experimental data show hadron gas fluctuation measures even at RHIC, where deconfinement is taken for granted. We will see how the dynamics of quark recombination washes out the quark-gluon plasma signal in the fluctuation criterion. Moreover, we will discuss briefly the problem of entropy at recombination. In a second application, the formation of exotic hadronic clusters, larger than usual mesons and baryons, is studied. Such clusters could provide new measures for the thermalization and homogenization of a deconfined gas of colour charges. Moreover, number estimates for exotic clusters from recombination are considerably lower than corresponding predictions from thermal models, providing a clear difference between statistical hadronization and hadronization via quark recombination. A detailed analysis is provided for pentaquark candidates such as the Theta-Plus. It turns out that the distribution of exotic states over strangeness, isospin, and spin could provide a sensitive measure for thermalization and decorrelation in the deconfined quark phase, if it could be measured.Diese Arbeit behandelt das molekulardynamische Simulationsmodell qMD (Quark-Molekulardynamik), das im Zusammenhang mit der Untersuchung der Hadronisierung eines Quark-Gluon-Plasmas zur Berücksichtigung des Farbfreiheitsgrades der elementaren Materie verwendet wird. Das qMD-Modell leistet eine dynamische Beschreibung der Bildung von Hadronen über die Rekombination von Quarks und Antiquarks. In der Quark-Molekulardynamik qMD werden Quarks und Antiquarks als klassische, relativistische Punktteilchen behandelt, die eine Farbladung tragen und über ein langreichweitiges Cornell-Potential wechselwirken. Diese Potentialwechselwirkung trägt den Gluonfreiheitsgraden Rechnung: Gluonen werden nicht explizit als Teilchen behandelt. Es werden vier verschiedene Quarkflavours (up, down, strange und charm) mit ihren Strommassen berücksichtigt. Es zeigt sich, daß die dynamische Entwicklung eines Systems von Farbladungen zur Ausbildung farbneutraler Cluster führt. Diese unterliegen trotz der enormen Stärke der Farbpaarpotentiale einer nur noch sehr schwachen Restwechselwirkung und können daher als Hadronen angesehen werden. Hadronisierung kann dann dynamisch beschrieben werden, indem jedem farbneutralen Cluster ein Hadron oder eine hadronische Resonanz zugeordnet wird. Im thermischen Gleichgewicht weist das qMD-Modell einen Übergang zwischen einer Phase mit Clusterbildung und Farbeinschluß bei tiefen Temperaturen und einer Phase frei beweglicher Farbladungen bei hohen Temperaturen und/oder Dichten auf, wie er von stark wechselwirkender Materie erwartet wird. An diesem Übergang wird die Zustandsgleichung weich, während Energiedichte und Druck der frei beweglichen Farbladungen ansteigen und sich bei hohen Temperaturen dem Stefan-Boltzmann-Grenzwert eines idealen Gases annähern. Es folgt die Anwendung des qMD-Modells auf die Beschreibung ultrarelativistischer Schwerionenkollisionen. Der Anfangszustand für die Quarkdynamik wird dabei durch das hadronische Transportmodell UrQMD bereitgestellt. Das so initialisierte Gas von Farbladungen expandiert und bildet farbneutrale Cluster, die auf Hadronen abgebildet werden. Das qMD-Modell erlaubt einen vollen Zugriff auf die dreidimensionale raumzeitliche Entwicklung des Systems einschließlich der vollständigen Phasenraumverteilungen. Es zeigt sich, daß die dabei ablaufenden dynamischen Prozesse im allgemeinen nicht dem thermischen Gleichgewicht folgen. Ein Vergleich von Resultaten der qMD-Simulationen mit Meßdaten für Schwefel-Gold-Kollisionen belegt, daß das qMD-Modell Phasenraumverteilungen der Hadronen im Endzustand der Kollision sehr gut wiedergibt. Die wirkliche Stärke des qMD-Modells liegt in dem Zugriff auf die Dynamik der Quark- und Antiquarkfreiheitsgrade. Es eignet sich daher hervorragend zur Untersuchung von Fluktuationen in der Quarkphase und deren Schicksal während der Hadronisierung sowie zur dynamischen Beschreibung der Bildung farbneutraler Cluster, einschließlich sogenannter exotischer hadronischer Zustände. So wird das Problem der ereignisweisen Fluktuationen der elektrischen Ladung als Nachweiskriterium für das Quark-Gluon-Plasma im Rahmen von qMD behandelt. Es zeigt sich, daß die Hadronisierung auf dem Wege der Clusterbildung und Rekombination Fluktuationssignale auslöscht, die eigentlich für ein Quark-Gluon-Plasma erwartet werden. Dies deckt sich mit dem experimentellen Befund, daß auch bei höchsten Energien wider Erwarten anhand der Ladungsfluktuationen kein Hinweis auf die Quarkphase drittelzahliger Ladungen gefunden werden konnte. Das Thema exotischer Hadronen hat durch den kürzlichen, wenn auch strittigen Nachweis des Pentaquark-Zustandes Theta-Plus großes Interesse erfahren. Ausgehend von der Idee, daß die Hadronisierung eines Quark-Gluon-Plasmas durch die Rekombination von farbneutralen Clustern ein günstiges Umfeld für die Entstehung solcher höherer Multiplett-Zustände liefert, wird die Bildung von Clustern aus bis zu sechs Quarks oder Antiquarks untersucht. Hieraus kann eine Abschätzung für die Zahl der zu erwartenden Zustände gewonnen werden. Die Verteilung der exotischen Zustände über Seltsamkeit, Isospin und Spin zeigt, daß diese, so sie denn meßbar wäre, einen empfindlichen Sensor für die Thermalisierung und den Verlust von Korrelationen in der Quark-Phase bereitstellen könnte

Physics at BES-III

This physics book provides detailed discussions on important topics in $\tau$-charm physics that will be explored during the next few years at \bes3 . Both theoretical and experimental issues are covered, including extensive reviews of recent theoretical developments and experimental techniques. Among the subjects covered are: innovations in Partial Wave Analysis (PWA), theoretical and experimental techniques for Dalitz-plot analyses, analysis tools to extract absolute branching fractions and measurements of decay constants, form factors, and CP-violation and \DzDzb-oscillation parameters. Programs of QCD studies and near-threshold tau-lepton physics measurements are also discussed.Comment: Edited by Kuang-Ta Chao and Yi-Fang Wan

From zero-dimensional theories to inhomogeneous phases with the functional renormalization group

In this work, we study strongly interacting quantum field theories using the functional renormalization group (FRG) as our primary computational method. The goal is to facilitate FRG computations in the context of quantum chromodynamics (QCD) to study the phase structure of dense strong-interaction matter. The main part of this work is split into three chapters, differing in the space-time dimension of the theories under consideration. We begin by studying zero-dimensional theories, which ultimately involves solving ordinary integrals with complicated FRG flow equations. Initially, this might seem like an unnecessarily convoluted way to solve a simple problem. However, it is this very fact – applying the FRG to such simple theories – that allows us to gain enormous insights into the FRG in a rigorous manner. Arguably, the most relevant development is the novel understanding of FRG flow equations in a fluid-dynamic context. This allows for the application of methods and concepts from the highly developed field of computational fluid dynamics (CFD) to the FRG. Two key findings are the identification of bosonic (fermionic) fluctuations as convective (source- or sink-like) contributions to the FRG flow and the resulting link between the CFD concept of numerical entropy and the irreversibility of non-perturbative renormalization group (RG) flows. These developments serve as a vital stepping stone facilitating the following applications. We proceed with computations in the (1+1)-dimensional Gross-Neveu (GN) model. We use it to study spontaneous chiral symmetry breaking (χSB) – a phenomenon vital to the understanding of QCD. Using the previously established CFD methods for the FRG, we study the effects of fermionic and crucially bosonic quantum and thermodynamic fluctuations on spontaneous χSB. The main result of this part of our research is that thermal bosonic fluctuations prevent χSB in the (1+1)-dimensional GN model. We further study inhomogeneous χSB indirectly using a stability analysis in mean-field (MF) approximation, i.e., considering only fermionic fluctuations. Our research helps to establish this method as a robust tool for both qualitative and quantitative statements about inhomogeneous χSB. We conclude the main part of this thesis with our studies of the (3+1)-dimensional Quark-Meson (QM) model, which we primarily consider as a low-energy effective theory of QCD. We focus on inhomogeneous chiral condensates by studying the QM model within the FRG framework, using a position-dependent ansatz for the chiral condensate, viz. the chiral density wave (CDW) for which we have been able to derive explicit FRG flow equations. We again investigate the effects of fluctuations on spontaneous χSB by solving those flow equations in RG-consistent MF calculations. Thus establishing contact with existing literature results for the QM model with CDW condensates. These computations – incorporating only fermionic fluctuations – are a first step towards a complete solution of the derived flow equations using our established CFD methods

Introduction to Elementary Particle Physics

The third edition of this successful textbook has been redesigned to reflect the progress of the field in the last decade, including the latest studies of the Higgs boson, quark–gluon plasma, progress in flavour and neutrino physics and the discovery of gravitational waves. It provides undergraduate students with complete coverage of the basic elements of the Standard Model of particle physics, assuming the reader has done only introductory courses in nuclear physics, special relativity and quantum mechanics. Examples of fundamental experiments are highlighted before discussions of the theory, giving students an appreciation of how experiment and theory interplay in the development of physics. The author examines leptons, hadrons and quarks, before presenting the dynamics and the surprising properties of the charges of the different forces, concluding with a discussion on neutrino properties beyond the Standard Model

Hadrons and Quark–Gluon Plasma

Before matter as we know it emerged, the universe was filled with the primordial state of hadronic matter called quark–gluon plasma. This hot soup of quarks and gluons is effectively an inescapable consequence of our current knowledge about the fundamental hadronic interactions: quantum chromodynamics. This book covers the ongoing search to verify the prediction experimentally and discusses the physical properties of this novel form of matter. It begins with an overview of the subject, followed by a discussion of experimental methods and results. The second half of the book covers hadronic matter in confined and deconfined form, and strangeness as a signature of the quark-gluon phase. It is ideal as an introduction for graduate students, as well as providing a valuable reference for researchers already working in this and related fields. This title, first published in 2002, has been reissued as an Open Access publication

Physics at BES_III

There has recently been a dramatic renewal of interest in the subjects of hadron spectroscopy and charm physics. This renaissance has been driven in part by experimental reports of D-0(D) over bar (0) mixing and the discovery of narrow D-sJ states and a plethora of charmonium-like XY Z states at the B factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related X(1835) meson state at BESII. At the same time, lattice QCD is now coming of age, and we are entering a new era when precise, quantitative predictions from lattice QCD can be tested against experimental measurements. For example, the High Precision QCD (HPQCD) and United Kingdom QCD (UKQCD) collaboration's recent high-precision, unquenched calculation of f(D+) = 208 +/- 4 MeV has been found to agree with the CLEO-c collaboration measurement of f(D+) = 223 +/- 17 +/- 8 MeV - a precision level of similar to 8%. Intriguingly, this agreement does not extend to f(Ds), where the HPQCD + UKQCD result f(Ds) = 241 +/- 3 MeV is more than three standard deviations below the current world average experimental value f(Ds) = 276 +/- 9 MeV. Precision improvements, especially on the experimental measurements, are called for and will be of extreme interest. The BES-III experiment at BEPCII in Beijing, which will start operation in summer 2008, will accumulate huge data samples of 10 x 10(9) J/psi, 3 x 10(9) psi(2S), 30 million D (D) over bar or 2 million DS+DS--pairs per running year, respectively, running in the tau-charm theshold region. Coupled with currently available results from CLEO-c, BES-III will make it possible to study in detail, and with unprecedentedly high precision, light hadron spectroscopy in the decays of charmonium states and charmed mesons. In addition, about 90 million D (D) over bar pairs will be collected at BES-III in a three-year run at the psi(3770) peak. Many high precision measurements, including CKM matrix elements related to charm weak decays, decay constants f(D+) and f(Ds), Dalitz decays of three-body D meson decays, searches for CP violation in the charmed-quark sector, and absolute decay branching fractions, will be accomplished. BES-III analyses are likely to be essential in deciding if recently observed signs of mixing in the D-0(D) over bar (0) meson system are actually due to new physics or not. BES-III measurements of f(D+) and f(Ds) at the similar to 1% precision level will match the precision of lattice QCD calculations and provide the opportunity to probe the charged Higgs sector in some mass ranges that will be inaccessible to the LHC. With modern techniques and huge data samples, searches for rare, lepton-number violating, flavor violating and/or invisible decays of D-mesons, charmonium resonances, and tau-leptons will be possible. Studies of tau-charm physics could reveal or indicate the possible presence of new physics in the low energy region. This physics book provides detailed discussions on important topics in tau-charm physics that will be explored during the next few years at BES-III. Both theoretical and experimental issues are covered, including extensive reviews of recent theoretical developments and experimental techniques. Among the subjects covered are: innovations in Partial Wave Analysis (PWA), theoretical and experimental techniques for Dalitz-plot analyses, analysis tools to extract absolute branching fractions and measurements of decay constants, form factors, and CP-violation and D-0(D) over bar (0)-oscillation parameters. Programs of QCD studies and near-threshold tau-lepton physics measurements are also discussed

Hadrons and Quark–Gluon Plasma

Before matter as we know it emerged, the universe was filled with the primordial state of hadronic matter called quark–gluon plasma. This hot soup of quarks and gluons is effectively an inescapable consequence of our current knowledge about the fundamental hadronic interactions: quantum chromodynamics. This book covers the ongoing search to verify the prediction experimentally and discusses the physical properties of this novel form of matter. It begins with an overview of the subject, followed by a discussion of experimental methods and results. The second half of the book covers hadronic matter in confined and deconfined form, and strangeness as a signature of the quark-gluon phase. It is ideal as an introduction for graduate students, as well as providing a valuable reference for researchers already working in this and related fields. This title, first published in 2002, has been reissued as an Open Access publication