IX HADRON PHYSICS AND VII RELATIVISTIC ASPECTS OF NUCLEAR PHYSICS: A Joint Meeting on QCD and QCP

Introduction to Nonequilibrium Quantum Field Theory
View Description Hide DescriptionThere has been substantial progress in recent years in the quantitative understanding of the nonequilibrium time evolution of quantum fields. Important topical applications, in particular in high energy particle physics and cosmology, involve dynamics of quantum fields far away from the ground state or thermal equilibrium. In these cases, standard approaches based on small deviations from equilibrium, or on a sufficient homogeneity in time underlying kinetic descriptions, are not applicable. A particular challenge is to connect the far‐from‐equilibrium dynamics at early times with the approach to thermal equilibrium at late times. Understanding the “link” between the early‐ and the late‐time behavior of quantum fields is crucial for a wide range of phenomena. For the first time questions such as the explosive particle production at the end of the inflationary universe, including the subsequent process of thermalization, can be addressed in quantum field theory from first principles. The progress in this field is based on efficient functional integral techniques, so‐called n‐particle irreducible effective actions, for which powerful nonperturbative approximation schemes are available. Here we give an introduction to these techniques and show how they can be applied in practice. Though we focus on particle physics and cosmology applications, we emphasize that these techniques can be equally applied to other nonequilibrium phenomena in complex many body systems.

Thermodynamics of the high temperature Quark‐Gluon Plasma
View Description Hide DescriptionThese lectures are a brief introduction to some of the weak coupling techniques used to decribe the physics of the quark‐gluon plasma at high temperature.

Three lectures on the Color Glass Condensate
View Description Hide DescriptionWe summarize the theory and phenomenology of the Color Glass Condensate reviewed previously by E. Iancu and the author in hep‐ph/0303204. We discuss some of the subsequent developments in the past year both in theory and in phenomenological applications.

Higgs picture of the QCD‐vacuum
View Description Hide DescriptionThe functional integral for QCD is reformulated by introducing explicitly an integration over the fluctuations of composite quark‐antiquark bound states. Chiral symmetry breaking by the color singlet scalar field induces masses for the fermions. Our formulation with scalar fluctuations may be useful for lattice gauge theories by modifying the spectrum of the Dirac operator in the vacuum and permitting a simple connection to chiral perturbation theory. We propose that a “condensate” of quark‐antiquark bound states in the color octet channel generates masses of the gluons by the Higgs mechanism. A simple effective action for quarks, gluons and (composite) scalars yields a surprisingly good description of the charges, masses and interactions of all low mass physical excitations — baryons, pseudoscalars and vector mesons. Dressed quarks appear as baryons and dressed gluons as vector mesons.

Thermalization at RHIC
View Description Hide DescriptionIdeal hydroynamics provides an excellent description of all aspects of the single‐particle spectra of all hadrons with transverse momenta below about 1.5‐2 GeV/c at RHIC. This is shown to require rapid local thermalization at a time scale below 1 fm/c and at energy densities which exceed the critical value for color deconfinement by an order of magnitude. The only known thermalized state at such energy densities is the quark‐gluon plasma (QGP). The rapid thermalization indicates that the QGP is a strongly interacting liquid rather than the weakly interacting gas of quarks and gluons that was previously expected.

Strangeness observables and pentaquarks
View Description Hide DescriptionWe review the experimental evidence on firstly, strangeness production as a signature for the QCD phase transition and secondly, pentaquarks, the latest and most exotic manifestations of strangeness in hadrons.

Strangeness Excitation Function in Heavy Ion Collisions
View Description Hide DescriptionWe study as function of energy strangeness created in relativistic heavy ion collisions. We consider statistical hadronization with chemical freeze‐out in both equilibrium and nonequilibrium. We present strangeness per baryon and per entropy in the energy range of SPS and RHIC. A baryon density independent evaluation of the kaon to pion ratio is presented.

Pion Dynamics at Finite Temperature and Density
View Description Hide DescriptionThe density corrections, in terms of the isospin chemical potential μ_{1} to the mass of the pions are studied in the framework of the SU (2) low energy effective chiral lagrangian in the two phases: The normal phase μ_{1} < m _{π} and the condensed phase μ_{1} > m _{π}. The pion decay constant f _{π}(T,μ_{1}) is also analyzed in the first phase. As a function of temperature for μ_{1} = 0, the mass remains quite stable, starting to grow for very high values of T, confirming previous results. However, there are interesting corrections to the mass when both effects (temperature and chemical potential) are simultaneously present. At zero temperature the π^{±} should condense when μ_{1} = ±m _{π}. This is not longer valid anymore at finite T. The mass of the π_{0} acquires also a non trivial dependence on μ_{1} due to the finite temperature. In the second phase we are able to calculate the thermal and density evolution of masses in the limits where μ_{1} ≫ m and where μ_{1} ∼ m. We also identified the phase transition curve.

Electroweak amplitudes in chiral quark models
View Description Hide DescriptionAfter referring to some basic features of chiral models for baryons, with quarks and mesons, we describe how to construct model states representing physical baryons. We consider soliton models such as the Linear Sigma Model or the Chromodielectric Model, and bag models such as the Cloudy Bag Model. These models are solved approximately using variational approaches whose starting point is a mean‐field description. We go beyond the mean‐field description by introducing quantum fluctuations in the mesonic degrees of freedom. This is achieved, in a first step, by using a quantum state to represent meson clouds and, secondly, by performing an angular momentum and isospin projection from the mean‐field state (actually a coherent state). Model states for baryons (nucleon, Delta, Roper) constructed in this way are used to determine several physical properties. I this seminar we paid a particular attention to the nucleon‐delta electromagnetic and weak transition, presenting the model predictions for the electromagnetic and axial amplitudes.

Running coupling constant from lattice studies of gluon and ghost propagators
View Description Hide DescriptionWe present a numerical study of the running coupling constant in four‐dimensional pure‐ SU (2) lattice gauge theory. The running coupling is evaluated by fitting data for the gluon and ghost propagators in minimal Landau gauge. Following Refs. [1, 2], the fitting formulae are obtained by a simultaneous integration of the β function and of a function coinciding with the anomalous dimension of the propagator in the momentum subtraction scheme. We consider these formulae at three and four loops. The fitting method works well, especially for the ghost case, for which statistical error and hyper‐cubic effects are very small. Our present result for Λ_{ MS } is MeV, where the error is purely systematic. We are currently extending this analysis to five loops in order to reduce this systematic error.

Time Dependence of QCD and Experimental Tests
View Description Hide DescriptionFrom astrophysics there are indications that the finestructure constant α has changed during the past 10 billion years. Within grand unification one can deduce that also the QCD scale has changed. Tests for a time variation of this scale are described. The result of the experiment in Munich is discussed.

RHIC Physics: The Color Glass Condensate and the Quark Gluon Plasma
View Description Hide DescriptionI discuss two forms of QCD matter which may be produced at RHIC. I conclude from the available empirical evidence that an equilibrated, but strongly coupled Quark Gluon Plasma has been made in such collisions. I also discuss the growing body of evidence that its source is a Color Glass Condensate.

Collective Flow signals the Quark Gluon Plasma
View Description Hide DescriptionA critical discussion of the present status of the CERN experiments on charm dynamics and hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A⋅GeV: here the hydrodynamic model has predicted the collapse of the v _{1}‐flow and of the v _{2}‐flow at ∼ 10 A⋅GeV; at 40 A⋅GeV it has been recently observed by the NA49 collaboration. Since hadronic rescattering models predict much larger flow than observed at this energy we interpret this observation as potential evidence for a first order phase transition at high baryon density ρ_{ B }. A detailed discussion of the collective flow as a barometer for the equation of state (EoS) of hot dense matter at RHIC follows. Additionally, detailed transport studies show that the away‐side jet suppression can only partially (< 50%) be due to hadronic rescattering. We, finally, propose upgrades and second generation experiments at RHIC which inspect the first order phase transition in the fragmentation region, i.e. at μ_{ B } ≈ 400 MeV (y ≈ 4 – 5), where the collapse of the proton flow should be seen in analogy to the 40 A⋅GeV data. The study of Jet‐Wake‐riding potentials and Bow shocks — caused by jets in the QGP formed at RHIC — can give further information on the equation of state (EoS) and transport coefficients of the Quark Gluon Plasma (QGP).

Multi‐Module Modeling of Heavy Ion Reactions and the 3rd Flow Component
View Description Hide DescriptionFluid dynamical calculations with QGP showed a softening of the directed flow while with hadronic matter this effect is absent. On the other hand, we indicated that a third flow component shows up in the reaction plane as an enhanced emission, which is orthogonal to the directed flow. This is not shadowed by the deflected projectile and target, and shows up at measurable rapidities, y_{c}m = 1 – 2. To study the formation of this effect initial stages of relativistic heavy ion collisions are studied. An effective string rope model is presented for heavy ion collisions at RHIC energies. Our model takes into account baryon recoil for both target and projectile, arising from the acceleration of partons in an effective field. The typical field strength (string tension) for RHIC energies is about 5–12 GeV/fm, what allows us to talk about “string ropes”. The results show that QGP forms a tilted disk, such that the direction of the largest pressure gradient stays in the reaction plane, but deviates from both the beam and the usual transverse flow directions. The produced initial state can be used as an initial condition for further hydrodynamical calculations. Such initial conditions lead to the creation of third flow component. Recent v _{1} measurements are promising that this effect can be used as a diagnostic tool of the QGP. Collective flow is sensitive to the early stages of system evolution. To study the sensitivity of the flow signal, we have calculated flow harmonics from a Blast Wave model, a tilted, ellipsoidally expanding source. We studied recent experimental techniques used for calculation of the v_{n} Fourier coefficients and pointed out a few possible problems connected to these techniques, which may impair the sensitivity of flow analysis.

Physics with Heavy Ions at LHC
View Description Hide DescriptionWe discuss the motivation to study heavy‐ion collisions at LHC, and the experimental conditions under which detectors will have to operate. A short description of the detectors under construction is given. Physics performance is illustrated on two examples, which will became accessible at LHC energies, jet quenching and heavy‐flavor production.

Cronin effect and high‐p _{⊥} suppression from the Color Glass Condensate
View Description Hide DescriptionI give a pedagogical survey of the nuclear collective effects associated with gluon saturation and their impact on particle production in high‐energy proton (or deuteron)‐nucleus collisions at RHIC. At central rapidity, the theory predicts a Cronin peak due to independent multiple scattering off the valence quarks in the nucleus. At forward rapidities, the peak flattens out and disappears very fast, because of the correlations induced through quantum evolution in the nuclear gluon distribution at small x. Also, the ratio R _{pA} between the particle yield in proton‐nucleus and proton‐proton collisions is rapidly suppressed when increasing the rapidity, because of saturation effects which slow down the evolution of the nucleus compared to that of the proton. This behaviour could be responsible for a similar trend observed in the deuteron‐nucleus collisions at RHIC.

Ultra‐High Energy Cosmic Rays
View Description Hide DescriptionWe give a general introduction to high‐energy cosmic ray physics before discussing somewhat more in detail new results concerning solutions of the cascade equations for the air shower evolution.

Diquark and Baryon Properties and their Production Cross Sections in dense and hot Matter
View Description Hide DescriptionUsing an extended version of the Nambu Jona‐Lasinio Lagrangian we calculate the properties of diquarks and baryons in dense and hot hadronic matter. These properties are then used to calculate the production cross sections of diquarks and baryons at finite temperature.

Schwinger‐Dyson Equations and Dynamical gluon mass generation
View Description Hide DescriptionWe obtain a solution for the gluon propagador in Landau gauge within two distinct approximations for the Schwinger‐Dyson equations (SDE). The first, named Mandelstam’s approximation, consist in neglecting all contributions that come from fermions and ghosts fields while in the second, the ghosts fields are taken into account leading to a coupled system of integral equations. In both cases we show that a dynamical mass for the gluon propagator can arise as a solution.

Mappings From Models Presenting Topological Mass Mechanisms to Purely Topological Models
View Description Hide DescriptionWe duscuss a class of mappings between the fields of the Cremmer‐Sherk and pure BF model in 4D. These mappings are established both with an iterative procedure as well as with an exact mapping procedure. Related equivalences in 5D and 3D are discussed.