Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 05/05

The highly successful Belle experiment was located at the KEKB accelerator in Tsukuba, Japan. KEKB was an electron-positron ring accelerator running at the asymmetric energies of 8 GeV (e-) and 3.5 GeV (e+). The Belle experiment took data from 1999 to 2010, but was shut down in June 2010 in order to begin a major upgrade of the accelerator and the detector. Belle played a crucial role in the award of the 2008 Nobel Prize for Physics to M. Kobayashi and T. Maskawa. The main physics goal of Belle was the measurement of CP-violation in the B-meson system.

This mission, as well as the search for physics beyond the Standard Model, has been passed to the Belle II experiment located at the SuperKEKB accelerator, the direct successors of the Belle experiment and KEKB respectively. The precise measurement of CP-violation and the search for rare or "forbidden" decays of the B-meson and the tau-lepton as signals for New Physics relies heavily on a large number of recorded events and the precision with which B-meson and lepton decay vertices can be reconstructed. Thus, the accelerator upgrade aims for an increase of the luminosity by a factor of 40, resulting in a peak luminosity of 8x10^35 cm^{-2} s^{-1}. This upgrade is scheduled to be finished by 2017 and will result in asymmetric beam energies of 7 GeV (e-) and 4 GeV (e+), provided by beams with a vertical size of only 48 nm ("nano-beam optics"), a size that has never been reached at any particle collider before.

The accelerator upgrade will result in the desired increase of the collision rate of particles, while it will also inevitably lead to an increase in the background for all sub-detectors. The Belle detector would not have been able to handle the new background conditions expected at SuperKEKB, hence an upgrade of the Belle detector to the Belle II detector was necessary. Additionally the upgrade aims to increase the physics performance of the detector, making it more sensitive to the effects of New Physics. The detector upgrade will see improvements and redesigns of almost all subsystems as well as the inclusion of a whole new sub-detector, the PiXel vertex Detector (PXD). The introduction of the PXD will ensure that decay vertices are reconstructed with an extremely high precision in the harsh background conditions expected at Belle II. The PXD is a semi-conductor based particle tracking detector and will be the innermost sub-detector of Belle II. It offers excellent track and vertex reconstruction capabilities, while having a thickness of only 75 μm in order to minimise multiple scattering effects.

Due to the innovative concept of a high-luminosity nano-beam accelerator, the scale of background being produced at the future SuperKEKB cannot be derived from a traditional electron-positron collider and has, therefore, to be simulated using first-principle Monte Carlo techniques. This thesis focuses on a detailed study of the expected background for the pixel vertex detector at the upcoming Belle II experiment. It starts with a comprehensive summary of the key components of the SuperKEKB accelerator and the Belle II detector before delving into the details of the Belle II simulation and reconstruction framework basf2. It was decided to develop the basf2 framework from scratch, rather than adapting the software framework used at Belle. The changes made in the upgrade from the Belle to the Belle II detector, would have required major modifications of nearly all existing libraries.

This thesis continues by explaining, in detail, the measurement and analysis of an experiment conducted at Belle in 2010, shortly before the KEKB accelerator and the Belle detector were shut down. The experiment aimed at establishing the validity of a major background for the PXD, namely the two-photon process into an electron-positron pair, described by the Monte-Carlo generators KoralW and BDK, which have never been tested in the kinematical region relevant for the PXD. From a comparison ba

Gewitterzellen mit ihren negativen Begleiterscheinungen wie Starkregen, Hagel

oder Fallwinden verursachen Verspätungen sowie Flugausfälle und sind damit für

höhere Kosten der Airlines und Flughafenbetreiber verantwortlich. Eine verlässliche

Vorhersage von Gewittern bis zu mehreren Stunden könnte dagegen den

Entscheidungsträgern am Flughafen einen größeren zeitlichen Spielraum geben,

um auf mögliche Gewitterzellen angemessen zu reagieren und adäquate Maßnahmen

zu ergreifen. Zur Bereitstellung zuverlässiger Gewittervorhersagen bis zu

sechs Stunden wurde Cb-LIKE am Deutschen Zentrum für Luft- und Raumfahrt

(DLR) entwickelt.

Der neue Gewittervorhersagealgorithmus wird in der vorliegenden Dissertation

detailliert vorgestellt. Cb-LIKE ist ein automatisiertes System, das unter

Verwendung von Modelldaten des COSMO-DE Wettermodells des Deutschen

Wetterdienstes (DWD) Gebiete ausweist, die eher für oder gegen eine Entwicklung

von Gewittern sprechen. Vier atmosphärische Parameter (CAPE, Vertikalwind,

Radarreflektivität und Temperatur an der Wolkenobergrenze) fließen in

das System ein. Eine neu entwickelte „Best-Member-Selection“ sorgt dabei durch

einen Abgleich zur aktuellen Gewittersituation für die automatische Auswahl des

realistischsten Modelllaufes aus einem Ensemble. Dadurch wird die beste Datengrundlage

für die Berechnung der Gewittervorhersagen gewährleistet. Für die

Auswahl des besten Members stehen vier verschiedene Modi zur Verfügung. Ein

neu entwickeltes Fuzzy-Logik System ermöglicht anschließend die Kombination

der Modelldaten und die Berechnung eines Gewitterindikators von 11,6¯6 bis 88,3¯3

für jeden Gitterpunkt des Modells für die nächsten sechs Stunden in stündlichen

Intervallen. Je höher der Wert des Indikators, desto mehr sprechen die Modellparameter

für die Entstehung von Gewittern. Zusätzlich wird die Vorhersagequalität

des neuen Algorithmus anhand einer umfassenden Verifikation unter Verwendung

einer „neighbourhood-verification“ Technik und von „multi-event contingency tables“

untersucht. Für die Sommerperiode 2012 weist Cb-LIKE im Vergleich zur

COSMO-DE Radarreflektivität bessere Werte in den Verifikationsgrößen auf. So

ist das „Fehlalarmverhältnis“ für den neuen Algorithmus niedriger (0,48 zu 0,56),

die „Wahrscheinlichkeit der Detektion“ (0,52 zu 0,45) und der „Critical Success

Index“ (0,50 zu 0,48) fallen dagegen höher aus. Die Resultate zeigen, dass der Cb-

LIKE Algorithmus eine sinnvolle neue Methodik für Gewittervorhersagen von hoher

Qualität auf der Datenbasis des COSMO-DE Modells darstellt. Die Ergebnisse

aus der Verifikation ermöglichen außerdem die Übersetzung des Cb-LIKE Indikatorfeldes

in die gewünschten probabilistischen Gewittervorhersagen. Zusätzlich

wird die erfolgreiche Implementierung der Cb-LIKE Gewittervorhersagen in das

WxFUSION System, eine graphische Benutzeroberfläche, vorgestellt.

This thesis deals with Double Field Theory (DFT), an effective field theory capturing the low energy dynamics of closed strings on a torus. All observables arising from those dynamics match on certain families of background space times. These different backgrounds are connected by T-duality. DFT renders T-duality on a torus manifest by adding D windig coordinates in addition to the D space time coordinates. An essential consistency constraint of the theory, the strong constraint, only allows for fields which depend on half of the coordinates of the arising doubled space.

An important application of DFT are generalized Scherk-Schwarz compactifications. They give rise to half-maximal, electrically gauged supergravities which are classified by the embedding tensor formalism, specifying the embedding of their gauge group into O(n,n). Because it is not compatible with all solutions of the embedding tensor, the strong constraint is replaced by the closure constraint of DFT's flux formulation. This allows for compactifications on backgrounds which are not T-dual to well-defined geometric ones. Their description requires non-geometric fluxes. Due to their special properties, they are also of particular phenomenological interest. However, the violation of the strong constraint obscures their uplift to full string theory. Moreover, there is an ambiguity in generalizing traditional Scherk-Schwarz compactifications to the doubled space of DFT: There is a lack of a general procedure to construct the twist of the compactification.

After reviewing DFT and generalized Scherk-Schwarz compactifications, DFT_WZW, a generalization of the current formalism is presented. It captures the low energy dynamics of a closed bosonic string propagating on a compact group manifold and it allows to solve the problems mentioned above. Its classical action and the corresponding gauge transformations arise from Closed String Field Theory up to cubic order in the massless fields. These results are rewritten in terms of a generalized metric and extended to all orders in the fields. There is an explicit distinction between background and fluctuations. For the gauge algebra to close, the latter have to fulfill a modified strong constraint, while for the former the closure constraint is sufficient. Besides the generalized diffeomorphism invariance known from the traditional formulation, DFT_WZW is invariant under standard diffeomorphisms of the doubled space. They are broken by imposing the totally optional extended strong constraint. In doing so, the traditional formulation is restored. A flux formulation for the new theory is derived and its connection to generalized Scherk-Schwarz compactifications is discussed. Further, a possible tree-level uplift of a genuinely non-geometric background (not T-dual to any geometric configuration) is presented. Finally, the ambiguity in constructing the compactification's twist is eliminated. Altogether, a more general picture of DFT and the structures it is based on emerges.

In this thesis we study the geometry and the low-energy effective physics associated with Abelian gauge groups in F-theory compactifications.

To construct suitable torus-fibered Calabi-Yau manifolds, we employ the framework of toric geometry. By identifying appropriate building blocks of Calabi-Yau manifolds that can be studied independently, we devise a method to engineer large numbers of manifolds that give rise to a specified gauge group and achieve a partial classification of toric gauge groups. Extending our analysis from gauge groups to matter spectra, we prove that the matter content of the most commonly studied F-theory set-ups is rather constrained. To circumvent such limitations, we introduce an algorithm to analyze torus-fibrations defined as complete intersections and present several novel kinds of F-theory compactifications. Finally, we show how torus-fibrations without section are linked to fibrations with multiple sections through a network of successive geometric transitions.

In order to investigate the low-energy effective physics resulting from our compactifications, we apply M- to F-theory duality. After determining the effective action of F-theory with Abelian gauge groups in six dimensions, we compare the loop-corrected Chern-Simons terms to topological quantities of the compactification manifold to read off the massless matter content. Under certain assumptions, we show that all gravitational and mixed anomalies are automatically canceled in F-theory. Furthermore, we compute the low-energy effective action of F-theory compactifications without section and suggest that the absence of a section signals the presence of an additional massive Abelian gauge field. Adjusting our analysis to four dimensions, we show that remnants of this massive gauge field survive as discrete symmetries that impose selection rules on the Yukawa couplings of the effective theory.

This thesis presents a study of the galaxy populations in massive galaxy clusters that have been selected via the Sunyaev - Zeldovich Effect from the South Pole Telescope. The clusters have multiband optical imaging data from the Dark Energy Survey (DES). Each cluster has a robust mass estimate and with the deep DES data they cover a redshift range between 0 and 1.1. This makes it an ideal cluster sample to study evolutionary trends of the galaxy populations with mass and redshift.