Measurement of the unpolarized K+ Lambda and K+ Sigma 0 electroproduction cross-section off the proton with KAOS-spectrometer

The new stage of the Mainz Microtron, MAMI, at the Institute for Nuclear Physics of the Johannes Gutenberg-University, operational since 2007, allows open strangeness experiments to be performed. Covering the lack of electroproduction data at very low Q2, p(e,K+)Lambda and p(e,K+)Sigma0, reactions have been studied at Q^2 = 0.036(GeV/c)^2 andrnQ^2 = 0.05(GeV=c)^2 in a large angular range. Cross-section at W=1.75rnGeV will be given in angular bins and compared with the predictions of Saclay-Lyon and Kaon Maid isobaric models. We conclude that the original Kaon-Maid model, which has large longitudinal couplings of the photon to nucleon resonances, is unphysical. Extensive studies for the suitability of silicon photomultipliers as read out devices for a scintillating fiber tracking detector, with potential applications in both positive and negative arms of the spectrometer, will be presented as well.

Modeling the gas and aqueous phase chemistry of the marine boundary layer

Ein eindimensionales numerisches Modell der maritimenGrenzschicht (MBL) wurde erweitert, um chemische Reaktionenin der Gasphase, von Aerosolpartikeln und Wolkentropfen zu beschreiben. Ein Schwerpunkt war dabei die Betrachtung derReaktionszyklen von Halogenen. Soweit Ergebnisse vonMesskampagnen zur Verfuegung standen, wurden diese zurValidierung des Modells benutzt. Die Ergebnisse von frueheren Boxmodellstudien konntenbestaetigt werden. Diese zeigten die saeurekatalysierteAktivierung von Brom aus Seesalzaerosolen, die Bedeutung vonHalogenradikalen fuer die Zerstoerung von O3, diepotentielle Rolle von BrO bei der Oxidation von DMS und dievon HOBr und HOCl in der Oxidation von S(IV). Es wurde gezeigt, dass die Beruecksichtigung derVertikalprofile von meteorologischen und chemischen Groessenvon grosser Bedeutung ist. Dies spiegelt sich darin wider,dass Maxima des Saeuregehaltes von Seesalzaerosolen und vonreaktiven Halogenen am Oberrand der MBL gefunden wurden.Darueber hinaus wurde die Bedeutung von Sulfataerosolen beidem aktiven Recyceln von weniger aktiven zu photolysierbarenBromspezies gezeigt. Wolken haben grosse Auswirkungen auf die Evolution und denTagesgang der Halogene. Dies ist nicht auf Wolkenschichtenbeschraenkt. Der Tagesgang der meisten Halogene ist aufgrundeiner erhoehten Aufnahme der chemischen Substanzen in die Fluessigphase veraendert. Diese Ergebnisse betonen dieWichtigkeit der genauen Dokumentation der meteorologischenBedingungen bei Messkampagnen (besonders Wolkenbedeckungsgrad und Fluessigwassergehalt), um dieErgebnisse richtig interpretieren und mit Modellresultatenvergleichen zu koennen. Dieses eindimensionale Modell wurde zusammen mit einemBoxmodell der MBL verwendet, um die Auswirkungen vonSchiffemissionen auf die MBL abzuschaetzen, wobei dieVerduennung der Abgasfahne parameterisiert wurde. DieAuswirkungen der Emissionen sind am staerksten, wenn sie insauberen Gebieten stattfinden, die Hoehe der MBL gering istund das Einmischen von Hintergrundluft schwach ist.Chemische Reaktionen auf Hintergrundaerosolen spielen nureine geringe Rolle. In Ozeangebieten mit schwachemSchiffsverkehr sind die Auswirkungen auf die Chemie der MBL beschraenkt. In staerker befahrenen Gebieten ueberlappensich die Abgasfahnen mehrerer Schiffe und sorgen fuerdeutliche Auswirkungen. Diese Abschaetzung wurde mitSimulationen verglichen, bei denen die Emissionen alskontinuierliche Quellen behandelt wurden, wie das inglobalen Chemiemodellen der Fall ist. Wenn die Entwicklungder Abgasfahne beruecksichtigt wird, sind die Auswirkungendeutlich geringer da die Lebenszeit der Abgase in der erstenPhase nach Emission deutlich reduziert ist.

Tracking, b-tagging and measurement of the b-jet production cross section with the ATLAS detector

The Standard Model of elementary particle physics was developed to describe the fundamental particles which constitute matter and the interactions between them. The Large Hadron Collider (LHC) at CERN in Geneva was built to solve some of the remaining open questions in the Standard Model and to explore physics beyond it, by colliding two proton beams at world-record centre-of-mass energies. The ATLAS experiment is designed to reconstruct particles and their decay products originating from these collisions. The precise reconstruction of particle trajectories plays an important role in the identification of particle jets which originate from bottom quarks (b-tagging). This thesis describes the step-wise commissioning of the ATLAS track reconstruction and b-tagging software and one of the first measurements of the b-jet production cross section in pp collisions at sqrt(s)=7 TeV with the ATLAS detector. The performance of the track reconstruction software was studied in great detail, first using data from cosmic ray showers and then collisions at sqrt(s)=900 GeV and 7 TeV. The good understanding of the track reconstruction software allowed a very early deployment of the b-tagging algorithms. First studies of these algorithms and the measurement of the b-tagging efficiency in the data are presented. They agree well with predictions from Monte Carlo simulations. The b-jet production cross section was measured with the 2010 dataset recorded by the ATLAS detector, employing muons in jets to estimate the fraction of b-jets. The measurement is in good agreement with the Standard Model predictions.

Forward modelling of petrological crust-forming processes on the early Earth

Tonalite-trondhjemite-granodiorite (TTG) gneisses form up to two-thirds of the preserved Archean continental crust and there is considerable debate regarding the primary magmatic processes of the generation of these rocks. The popular theories indicate that these rocks were formed by partial melting of basaltic oceanic crust which was previously metamorphosed to garnet-amphibolite and/or eclogite facies conditions either at the base of thick oceanic crust or by subduction processes.rnThis study investigates a new aspect regarding the source rock for Archean continental crust which is inferred to have had a bulk compostion richer in magnesium (picrite) than present-day basaltic oceanic crust. This difference is supposed to originate from a higher geothermal gradient in the early Archean which may have induced higher degrees of partial melting in the mantle, which resulted in a thicker and more magnesian oceanic crust. rnThe methods used to investigate the role of a more MgO-rich source rock in the formation of TTG-like melts in the context of this new approach are mineral equilibria calculations with the software THERMOCALC and high-pressure experiments conducted from 10–20 kbar and 900–1100 °C, both combined in a forward modelling approach. Initially, P–T pseudosections for natural rock compositions with increasing MgO contents were calculated in the system NCFMASHTO (Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–TiO2) to ascertain the metamorphic products from rocks with increasing MgO contents from a MORB up to a komatiite. A small number of previous experiments on komatiites showed the development of pyroxenite instead of eclogite and garnet-amphibolite during metamorphism and established that melts of these pyroxenites are of basaltic composition, thus again building oceanic crust instead of continental crust.rnThe P–T pseudosections calculated represent a continuous development of their metamorphic products from amphibolites and eclogites towards pyroxenites. On the basis of these calculations and the changes within the range of compositions, three picritic Models of Archean Oceanic Crust (MAOC) were established with different MgO contents (11, 13 and 15 wt%) ranging between basalt and komatiite. The thermodynamic modelling for MAOC 11, 13 and 15 at supersolidus conditions is imprecise since no appropriate melt model for metabasic rocks is currently available and the melt model for metapelitic rocks resulted in unsatisfactory calculations. The partially molten region is therfore covered by high-pressure experiments. The results of the experiments show a transition from predominantly tonalitic melts in MAOC 11 to basaltic melts in MAOC 15 and a solidus moving towards higher temperatures with increasing magnesium in the bulk composition. Tonalitic melts were generated in MAOC 11 and 13 at pressures up to 12.5 kbar in the presence of garnet, clinopyroxene, plagioclase plus/minus quartz (plus/minus orthopyroxene in the presence of quartz and at lower pressures) in the absence of amphibole but it could not be explicitly indicated whether the tonalitic melts coexisting with an eclogitic residue and rutile at 20 kbar do belong to the Archean TTG suite. Basaltic melts were generated predominantly in the presence of granulite facies residues such as amphibole plus/minus garnet, plagioclase, orthopyroxene that lack quartz in all MAOC compositions at pressures up to 15 kbar. rnThe tonalitic melts generated in MAOC 11 and 13 indicate that thicker oceanic crust with more magnesium than that of a modern basalt is also a viable source for the generation of TTG-like melts and therefore continental crust in the Archean. The experimental results are related to different geologic settings as a function of pressure. The favoured setting for the generation of early TTG-like melts at 15 kbar is the base of an oceanic crust thicker than existing today or by melting of slabs in shallow subduction zones, both without interaction of tonalic melts with the mantle. Tonalitic melts at 20 kbar may have been generated below the plagioclase stability by slab melting in deeper subduction zones that have developed with time during the progressive cooling of the Earth, but it is unlikely that those melts reached lower pressure levels without further mantle interaction.rn

High mobility rates during the period of the "Celtic migrations"? - 87 Sr, 86 Sr and delta 18 O evidence from Early La Tène Europe

Although the period of the historic “Celtic migrations” is archaeologically extensively studied, the long-lasting question whether mass migration or increased individual mobility caused the expansion of the La Tène culture throughout continental Europe persist. Strontium (Sr) and in part oxygen (O) isotope analysis of human remains from the early La Tène cemeteries of Nebringen (Germany), Münsingen-Rain (Switzerland), Monte Bibele (Italy) and the Czech cemeteries of Radovesice I, Radovesice II and Kutná Hora was, therefore, carried out to investigate the importance of residential changes during this time period. These isotope analyses showed that most analysed individuals either came from the area they were buried in or from the surrounding area of the cemetery. An exception was formed by the Czech cemeteries, where almost a quarter of the studied individuals appeared non-local. Together with Nebringen, these cemeteries also had the most varied Sr isotope ratios, which suggest highly mobile communities in which individuals regularly changed their residency. The isotopic ratios of the cemeteries of Münsingen-Rain and Monte Bibele appeared far less varied. In part, these differences might be explained by the community structures of these cemeteries. Morphological kinship analysis in Münsingen-Rain demonstrated biological relatedness among most of the analysed individuals. These related individuals also shared similar isotope signatures, which suggest an origin from the surrounding Aar Valley. In the vicinity of the cemetery of Monte Bibele, an associated settlement site was discovered. The deceased presumably not only shared this settlement, but also cultivated the same land plots. Dispersed settlement structures were suggested for Nebringen, Radovesice and Kutná Hora, as these agriculturally favourable landscapes were densely populated during prehistoric times. Connected to these community structures are the prevailing geological conditions in these areas. Both Münsingen-Rain and Monte Bibele are located in a region where homogeneous geological conditions prevail, whereas the landscapes of Nebringen, Radovesice and Kutná Hora are characterised by complex heterogeneous geological conditions. As the majority of individuals in Nebringen and the Czech cemeteries correspond to the expected isotope values for the studied areas, regularly changing land plots might have contributed to the observed variation. Although mass migration as depicted by the historical sources was not observed individual mobility of a small part of these studied communities certainly played a role. Males appeared, thereby, to have slightly more often a non-local birthplace or moved during childhood. Male mobility was, however, not always associated with burial as a warrior. Females, on the other hand, originated more often from the region. Patrilocal residential patterns, with the exception of the Czech cemeteries, were nevertheless not observed. Objects and ideas also seem to have been exchanged freely, as there are no indications that individuals with particular grave goods came from specific areas. It rather appears that the individuals buried with them were either local or had different places of origin. This can be explained by the fact that the exact origin of grave goods is difficult to establish and the occurrence of similar 87Sr/86Sr values in different areas. This study provided important new insights on the period of the “Celtic migrations” and the way of life of these prehistoric people.