Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 04/05

Germanium detectors are a choice technology in fundamental research. They are suitable for the

search for rare events due to their high sensitivity and excellent energy resolution. As an example, the GERDA (GERmanium Detector Array) experiment searching for neutrinoless double

beta decay is described. The observation of this decay would resolve the fundamental question

whether the neutrino is its own antiparticle. Especially adapted detector technologies and low

background rates needed to detect very rare events such as neutrinoless double beta decays are

discussed. The identification of backgrounds originating from the interaction of radiation, especially alpha-particles, is a focus of this thesis. Low background experiments face problems from alpha-particles due to unavoidable surface contaminations of the germanium detectors. The segmentation of detectors is used to obtain information about the special characteristics of selected events. The high precision test stand GALATEA was especially designed for surface scans of germanium detectors. As part of this work, GALATEA was completed and commissioned. The final

commissioning required major upgrades of the original design which are described in detail. Collimator studies with two commercial germanium detectors are presented. Different collimation

levels for a beta-source were investigated and crystal axis effects were examined. The first scan with an alpha-source of the passivated end-plate of a special 19-fold segmented prototype detector mounted in GALATEA is described. The alpha-induced surface events were studied and characterized. Crosstalk and mirror pulses seen in the segments of the germanium detector were analyzed. The detector studies presented in this thesis will help to further improve the design of germanium detectors for low background experiments.

This thesis unifies several studies, which all are dedicated to the subject of statistical data

analysis in radio astronomy and radio astrophysics.

Radio astronomy, like astronomy as a whole, has undergone a remarkable development in the past twenty years in introducing new instruments and technologies. New telescopes like the upgraded VLA, LOFAR, or the SKA and its pathfinder missions offer unprecedented sensitivities, previously uncharted frequency domains and unmatched survey capabilities.

Many of these have the potential to significantly advance the science of radio astrophysics and cosmology on all scales, from solar and stellar

physics, Galactic astrophysics and cosmic magnetic fields, to Galaxy cluster astrophysics

and signals from the epoch of reionization.

Since then, radio data analysis, calibration and imaging techniques have entered a similar phase of new development to push the boundaries and adapt the field to the new instruments and scientific opportunities.

This thesis contributes to these greater developments in two specific subjects, radio interferometric imaging and cosmic magnetic field statistics.

Throughout this study, different data analysis techniques are presented and employed

in various settings, but all can be summarized under the broad term of statistical infer-

ence. This subject encompasses a huge variety of statistical techniques, developed to solve

problems in which deductions have to be made from incomplete knowledge, data or measurements. This study focuses especially on Bayesian inference methods that make use of a subjective definition of probabilities, allowing for the expression of probabilities and statistical knowledge prior to an actual measurement.

The thesis contains two different sets of application for such techniques. First, situations

where a complicated, and generally ill-posed measurement problem can be approached by

assuming a statistical signal model prior to infer the desired measured variable. Such

a problem very often is met should the measurement device take less data then needed

to constrain all degrees of freedom of the problem. The principal case investigated in

this thesis is the measurement problem of a radio interferometer, which takes incomplete

samples of the Fourier transformed intensity of the radio emission in the sky, such that it is

impossible to exactly recover the signal. The new imaging algorithm RESOLVE is presented,

optimal for extended radio sources. A first showcase demonstrates the performance of the

new technique on real data. Further, a new Bayesian approach to multi-frequency radio

interferometric imaging is presented and integrated into RESOLVE.

The second field of application are astrophysical problems, in which the inherent stochas-

tic nature of a physical process demands a description, where properties of physical quanti-

ties can only be statistically estimated. Astrophysical plasmas for instance are very often in a turbulent state, and thus governed by statistical hydrodynamical laws. Two studies are presented that show how properties of turbulent plasma magnetic fields can be inferred from radio observations.

Two analyses searching for squarks and gluinos which decay into final states with multiple

jets, an isolated electron or muon and a large missing transverse energy are presented. Both rely on data taken by the ATLAS detector in

pp collisions at a center-of-mass energy of 8 TeV at the LHC during 2012. The first analysis uses a subset of 5.8 fb-1 of this dataset, the other analysis uses the full statistics of 20.3 fb-1.

Both analysis share the same methods regarding the triggers and the background estimation techniques. The two

dominant backgrounds are ttbar and W+jets production. The ttbar

and the W+jets backgrounds are estimated in a semi-data-driven method. The minor QCD multi-jet background is estimated in an entirely

data-driven method. The final background estimates in the analyses are derived in a profile-log-likelihood fit.

None of the analyses sees an excess beyond Standard Model expectations.

The analysis of the partial dataset derives limits in a MSUGRA/CMSSM model with parameters A_0=0, tan(beta) = 10

and mu > 0 and excludes squarks and gluinos with masses below 1.2 TeV for equal squark and gluino masses.

The analysis of the full dataset derives limits in simplified models and in a MSUGRA/CMSSM model with parameters A_0=-2 m_0,

tan(beta) = 30 and mu > 0. Gluinos (squarks) with masses below 1.2 TeV (750 GeV) can be excluded for vanishing LSP masses in simplified models. Gluino masses below 1.2 TeV can be excluded for every m_0 value in the MSUGRA/CMSSM model.

Why do we exist? CP violation is an integral part of this question as its understanding is crucial to explain the matter-antimatter asymmetry observed in our universe. Several experiments were designed and carried out to precisely measure CP violation, especially in the B meson system where large asymmetries where predicted and found. With Belle II and LHCb, two new experiments are going to improve the existing measurements. Belle II will be based on the very successful Belle experiment at the KEKB collider, currently

holding the world record on luminosity with 2.11×10³⁴ cm⁻²2s⁻¹.

The B meson system has a very rich decay topology and many of theses decay modes and their CP asymmetry parameters have already been measured at Belle. The most famous decay channel, B0⟶J/ψK0s, poses very tight constraints on sin 2φ₁ but leaves a twofold ambiguity on the actual value of the angle φ₁ in the CKM triangle. The decay mode B0⟶D*-D*+K0s, while experimentally much more challenging, offers the unique possibility to also extract cos2φ₁ and thus resolve this ambiguity.

In the first chapters of this thesis we present the principle of this measurement and the results for the branching fraction and the time-dependent CP violation parameters of B0⟶D*-D*+K0s decays. These results are obtained from the final data sample of the Belle experiment containing 772 million BBbar pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.

We obtain the branching fraction BR(B0⟶D*-D*+K0s) = (5.35+0.35−0.34(stat) ± 0.57(syst))×10⁻³, which is in agreement with the current world average. In a 3 parameter fit sensitive to cos2φ₁, we extract the currently most precise values for the CP parameters

Jc/J0 = 0.37 ± 0.10(stat) ± 0.02(syst), (2Js1/J0) sin(2φ₁) = 0.30 ± 0.16(stat) ± 0.03(syst), (2Js2/J0) cos(2φ₁) = 0.16 ± 0.16(stat) ± 0.03(syst). This allows us to exclude a negative value for cos2φ₁ at a 85% confidence under the assumption that that (2Js2/J0) is positive.

Finally, we describe the implementation of the vertex detector geometry for the upcoming Belle II experiment. The upgrade to Belle aims to increase the integrated luminosity by a factor of 50 and will receive, among other upgrades, a completely new vertex detector. To produce simulated events, a precise description of the sensor geometry and material budget is needed.

One of the most fundamental correlations between the properties of galaxies in the local Universe is the so-called morphology-density relation (Dressler 1980). A plethora of studies utilizing multi-wavelength tracers of activity have shown that late type star forming galaxies favour low density regions in the local Universe (e.g. G´omez et al. 2003). In particular, the cores of massive galaxy clusters are galaxy graveyards full of massive spheroids that are dominated by old stellar populations. A variety of physical processes might be effective in suppressing star formation and affecting the morphology of cluster and group galaxies. Broadly speaking, these can be grouped in two big families: (i) interactions with other cluster members and/or with the cluster gravitational potential and (ii) interactions with the hot gas that permeates massive galaxy systems. Galaxy groups are the most common galaxy environment in our Universe, bridging the gap between the low density field and the crowded galaxy clusters. Indeed, as many as 50%-70% of galaxies reside in galaxy groups in the nearby Universe (Huchra & Geller 1982; Eke et al. 2004), while only a few percent are contained in the denser cluster cores. In addition, in the current bottom-up paradigm of structure formation, galaxy groups are the building blocks of more massive systems: they merge to form clusters. As structures grow, galaxies join more and more massive systems, spending most of their life in galaxy groups before entering the cluster environment. Thus, it is plausible to ask if group-related processes may drive the observed relations between galaxy properties and their environment.

To shed light on this topic we have built the largest X-ray selected samples of galaxy groups with secure spectroscopic identification on the major blank field surveys. For this purpose, we combine deep X-ray Chandra and XMM data of the four major blank fields (All-wavelength Extended Groth Strip International Survey (AEGIS), the COSMOS field, the Extended Chandra Deep Field South (ECDFS), and the Chandra Deep Field North (CDFN) ). The group catalog in each field is created by associating any X-ray extended emission to a galaxy overdensity in the 3D space. This is feasible given the extremely rich spectroscopic coverage of these fields. Our identification method and the dynamical analysis used to identify the galaxy group members and to estimate the group velocity dispersion is extensively tested on the AEGIS field and with mock catalogs extracted from the Millennium Simulation (Springel et al. 2005). The effect of dynamical complexity, substructure, shape of X-ray emission, different radial and redshift cuts have been explored on the LX −sigma relation. We also discover a high redshift group at z~1.54 in the AEGIS field. This detection illustrates that mega-second Chandra exposures are required for detecting such objects in the volume of deep fields. We provide an accurate measure of the Star Formation Rate (SFR) of galaxies by using the deepest available Herschel PACS and Spitzer MIPS data available for the considered fields. We also provide a well-calibrated estimate of the SFR derived by using the SED fitting technique for undetected sources in mid- and far-infrared observations.

Using this unique sample, we conduct a comprehensive analysis of the dependence of the total SFR , total stellar masses and halo occupation distribution (HOD) of massive galaxies (M*>10^10 M_sun) on the halo mass of the groups with rigorous consideration of uncertainties. We observe a clear evolution in the level of star formation (SF) activity in galaxy groups. Indeed, the total star formation activity in high redshift

(0.5

We present a study of the galaxy populations in massive galaxy clusters selected by their Sunyaev–Zel’dovich Effect (SZE) signatures. Selection via the SZE is approximately mass- limited where the mass limit varies only slightly with redshift, making it an ideal selection method for studying the evolution of the galaxy content of clusters. We begin by introducing the SZE, the South Pole Telescope (SPT), and the larger research project in which this Thesis is embedded. We then present the core galaxy population studies of this Thesis.

In Chapter 3, we present the first large-scale follow-up of an SZE-selected galaxy cluster sample. Of 224 galaxy cluster candidates in the sample, we optically confirm 158 clusters and measure their photometric redshifts. We find a redshift range of 0.1