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In dieser Arbeit wurde gezeigt, ob Simulation und Messung der realen Struktur übereinstimmen. Dazu wurde mit Hilfe der Störkörpermessmethode über die Phasenverschiebung die elektrische Feldverteilung einer IH-Struktur bestimmt (unter Variation der Tunerhöhe). Die Feldverteilung von Simulation und Messung sind im Kurvenverlauf gleich, allerdings ist die Stärke der Simulationsfelder um einen Faktor 1,1 – 1,2 größer...
Lattice simulation of a center symmetric three dimensional effective theory for SU(2) Yang-Mills
(2010)
We present lattice simulations of a center symmetric dimensionally reduced effective field theory for SU(2) Yang Mills which employ thermal Wilson lines and three-dimensional magnetic fields as fundamental degrees of freedom. The action is composed of a gauge invariant kinetic term, spatial gauge fields and a potential for the Wilson line which includes a "fuzzy" bag term to generate non-perturbative fluctuations between Z(2) degenerate ground states. The model is studied in the limit where the gauge fields are set to zero as well as the full model with gauge fields. We confirm that, at moderately weak coupling, the "fuzzy" bag term leads to eigenvalue repulsion in a finite region above the deconfining phase transition which shrinks in the extreme weak-coupling limit. A non-trivial Z(N) symmetric vacuum arises in the confined phase. The effective potential for the Polyakov loop in the theory with gauge fields is extracted from the simulations including all modes of the loop as well as for cooled configurations where the hard modes have been averaged out. The former is found to exhibit a non-analytic contribution while the latter can be described by a mean-field like ansatz with quadratic and quartic terms, plus a Vandermonde potential which depends upon the location within the phase diagram. Other results include the exact location of the phase boundary in the plane spanned by the coupling parameters, correlation lengths of several operators in the magnetic and electric sectors and the spatial string tension. We also present results from simulations of the full 4D Yang-Mills theory and attempt to make a qualitative comparison to the 3D effective theory.
The aim of this work is to develop an effective equation of state for QCD, having the correct asymptotic degrees of freedom, to be used as input for dynamical studies of heavy ion collisions. We present an approach for modeling an EoS that respects the symmetries underlying QCD, and includes the correct asymptotic degrees of freedom, i.e. quarks and gluons at high temperature and hadrons in the low-temperature limit. We achieve this by including quarks degrees of freedom and the thermal contribution of the Polyakov loop in a hadronic chiral sigma-omega model. The hadronic part of the model is a nonlinear realization of an sigma-omega model. As the fundamental symmetries of QCD should also be present in its hadronic states such an approach is widely used to describe hadron properties below and around Tc. The quarks are introduced as thermal quasi particles, coupling to the Polyakov loop, while the dynamics of the Polyakov loop are controlled by a potential term which is fitted to reproduce pure gauge lattice data. In this model the sigma field serves a the order parameter for chiral restoration and the Polyakov loop as order parameter for deconfinement. The hadrons are suppressed at high densities by excluded volume corrections. As a next step, we introduce our new HQ model equation of state in a microscopic+macroscopic hybrid approach to heavy ion collisions. This hybrid approach is based on the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport approach with an intermediate hydrodynamical evolution for the hot and dense stage of the collision. The present implementation allows to compare pure microscopic transport calculations with hydrodynamic calculations using exactly the same initial conditions and freeze-out procedure. The effects of the change in the underlying dynamics - ideal fluid dynamics vs. non-equilibrium transport theory - are explored. The final pion and proton multiplicities are lower in the hybrid model calculation due to the isentropic hydrodynamic expansion while the yields for strange particles are enhanced due to the local equilibrium in the hydrodynamic evolution. The elliptic and directed flow are shown to be not sensitive to changes in the EoS while the smaller mean free path in the hydrodynamic evolution reflects directly in higher flow results which are consistent with the experimental data. This finding indicates qualitatively that physical mechanisms like viscosity and other non equilibrium effects play an essentially more important role than the EoS when bulk observables like flow are investigated. In the last chapter, results for the thermal production of MEMOs in nucleus-nucleus collisions from a combined micro+macro approach are presented. Multiplicities, rapidity and transverse momentum spectra are predicted for Pb+Pb interaction at different beam energies. The presented excitation functions for various MEMO multiplicities show a clear maximum at the upper FAIR energy regime making this facility the ideal place to study the production of these exotic forms of multistrange objects.
This dissertation is devoted to the study of thermodynamics for quantum gauge theories.The poor convergence of quantum field theory at finite temperature has been the main obstacle in the practical applications of thermal QCD for decades. In this dissertation I apply hard-thermal-loop perturbation theory, which is a gauge-invariant reorganization of the conventional perturbative expansion for quantum gauge theories to the thermodynamics of QED and Yang-Mills theory to three-loop order. For the Abelian case, I present a calculation of the free energy of a hot gas of electrons and photons by expanding in a power series in mD/T, mf /T and e2, where mD and mf are the photon and electron thermal masses, respectively, and e is the coupling constant.I demonstrate that the hard-thermal-loop perturbation reorganization improves the convergence of the successive approximations to the QED free energy at large coupling, e ~ 2. For the non-Abelian case, I present a calculation of the free energy of a hot gas of gluons by expanding in a power series in mD/T and g2, where mD is the gluon thermal mass and g is the coupling constant. I show that at three-loop order hard-thermal-loop perturbation theory is compatible with lattice results for the pressure, energy density, and entropy down to temperatures T ~ 2 - 3 Tc. The results suggest that HTLpt provides a systematic framework that can be used to calculate static and dynamic quantities for temperatures relevant at LHC.
The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars) project is an online
database (www.kadonis.org) for cross sections relevant to the s-process and the p-process.
The first version was an updated sequel to the previous Bao et al. [1] compilations from 1987
and 2000 for (n; g) cross sections relevant to Big Bang and s-process nucleosynthesis. The first
update, KADoNiS v0.2, was published in 2006 [2]. It contained mainly Maxwellian averaged
(n; g) cross sections relevant to the s-process, and some experimental charged particle induced
reaction relevant to the p-process. After that a second update was presented in 2009 [3].
Recently, we started to collect and review all existing experimental data relevant for p-process
nucleosynthesis and to provide a user-friendly database based on the KADoNiS framework. The
p-process part of the KADoNiS database is currently being extended and will include all available
experimental data from (p; g), (p;n), (p;a), (a,g), (a;n) and (a; p) reactions in or close to the
respective Gamow window.
The HADES (High Acceptance DiElectron Spectrometer) is an experimental
apparatus installed at the heavy-ion synchrotron SIS-18 at GSI, Darmstadt.
The main physics motivation of the HADES experiment is the measurement
of e+e− pairs in the invariant-mass range up to 1 GeV/c2 in heavy-ion collisions
as well as in pion and proton-induced reactions.
The HADES physics program is focused on in-medium properties of the light
vector mesons ρ(770), ω(783) and φ(1020), which decay with a small branching
ratio into dileptons. Dileptons are penetrating probes which allow to study
the in-medium properties of hadrons. However, in heavy-ion collisions, the
measurement of such lepton pairs is difficult because they are rare and have a
very large combinatorial background.
Recently, HADES has been upgraded with new detectors and new electronics
in order to handle higher intensity beams and reactions with heavy nuclei up
to Au.
HADES will continue for a few more years its rich physics program at its
current place at SIS-18 and then move to the upcoming international Facility
for Antiproton and Ion Research (FAIR) accelerator complex. In this context
the physics results presented in this work are important prerequisites for the investigation
of in-medium vector meson properties in p + A and A+A collisions.
This work consists of five chapters. The first chapter introduces the physics
motivation and a review of recent physics results. In the second chapter, the
HADES spectrometer is described and its sub-detectors are presented. Chapter
three deals with the issue of lepton identification and the reconstruction of
the dielectron spectra in p + p collisions is presented. Here, two reactions
are characterized: inclusive and exclusive dilepton production reactions. From
the spectra obtained, the corresponding cross sections are presented with the
respective statistical and systematical errors. A comparison with theoretical
models is included as well. Conclusions are given in chapter four.
The final part of this work is dedicated to the HADES upgrade, whose goal
is among others the achievement of a reliable and fast data acquisition of the
Multiwire Drift Chambers (MDCs). Chapter five presents my contribution to
this successful project during the three years of my stay at GSI.
We demonstrate that a Quark–Gluon Plasma (QGP) with a dilute admixture of heavy quarks has, in general, a lower speed of sound than a “pure” QGP without effects from heavy flavors. The change in the speed of sound is sensitive to the details of the theory, making the hydrodynamic response to “flavoring” a sensitive probe of the underlying microscopic dynamics. We suggest that this effect may be measured in ultrarelativistic heavy ion collisions by relating the event-by-event number of charm quarks to flow observables such as the average transverse momentum.
In der vorliegenden Arbeit wird die Gestaltung eines Teststandes für die optische Tomographie eines Ionenstrahles untersucht. Nachdem Ionenstrahlen hoher Intensität immer mehr Leistung in den Diagnosegeräten deponieren, müssen neue nicht Strahlzerstörende Diagnosemethoden gefunden werden. Die Diagnose mittels strahlinduziertem Restgasleuchten ist dabei eine viel versprechende nicht zerstörende Methode. Neben der Definition der Anforderungen für einen solchen Teststand werden verschiedene Realisierungsmöglichkeiten untersucht. Mit einem Testaufbau wird das strahlinduzierte Leuchten in Abhängigkeit verschiedener Restgase und Restgasdrücke untersucht, sowie die Eigenschaften des optischen Systems und der Kamera analysiert. Weiterhin wird die Möglichkeit der Emittanzbestimung aus einer optischen Aufnahme mit vorhandenen Methoden untersucht.
The isospin, spin and parity dependent potential of a pair of static-light mesons is computed using Wilson twisted mass lattice QCD with two flavors of degenerate dynamical quarks. From the results a simple rule can be deduced stating, which isospin, spin and parity combinations correspond to attractive and which to repulsive forces.
We compute the static-light baryon spectrum with Nf = 2 flavors of sea quarks using Wilson twisted mass lattice QCD. As light valence quarks we consider quarks, which have the same mass as the sea quarks with corresponding pion masses in the range 340MeV<∼ mPS<∼ 525MeV, as well as partially quenched quarks, which have the mass of the physical s quark. We extract masses of states with isospin I = 0,1/2,1, with strangeness S = 0,−1,−2, with angular momentum of the light degrees of freedom j = 0,1 and with parity P = +,−. We present a preliminary extrapolation in the light u/d and an interpolation in the heavy b quark mass to the physical point and compare with available experimental results.