Aufbau und Inbetriebnahme eines Protonen-Polarimeters an MAMI und Messung der Proton-Polarisation in der Reaktion p (e,e'p) pi 0 in paralleler Kinematik im Bereich der Delta(1232)-Resonanz

Das Detektorsystem des Spektrometers Ader Drei-Spektrometer-Anlage am MainzerElektronenbeschleuniger MAMI wurde im Rahmen dieser Arbeitum ein Fokalebenen-Proton-Polarimeter (FPP) ergänzt.Dazu wurden zwei Horizontale Doppeldriftkammern entworfenund zusammen mit einem Kohlenstoffanalysator hinter derFokalebene des Spektrometers aufgebaut.Zur Berechnung der Spin-Präzession in den inhomogenenMagnetfeldern des Spektrometers wurde das Programm QSPINerstellt und damit eine Spin-Transfer-Matrix (STM) erzeugt,mit der über eine Fitprozedur die Polarisationskomponentender Protonen in der Streuebene an die im FPP gemessenenangepaßt werden können.Mit elastischen Elektron-Proton-Streuexperimenten wurdenfalsche Asymmetrien im FPP untersucht, die berechnete STMbestätigt, die inklusive Proton-Kohlenstoff-Analysierstärkeauf einen größeren Streuwinkelbereich erweitert und dasVerhältnis zwischen dem elektrischen und dem magnetischenSachs-Formfaktor des Protons gemessen.Zur Untersuchung der Coulomb-Quadrupol-Übergangsamplitudebei der Anregung des Nukleons zur Delta(1232)-Resonanzwurden in einem Pion-Elektroproduktions-Experiment am Protonmit dem FPP die Komponenten der Polarisation derRückstoßprotonen in paralleler Kinematik gemessen.

A measurement of direct CP violation with the NA48 detector

Ziel des NA48 Experiments ist die Messung der direkten CPVerletzungim System der neutralen Kaonen. NA48 misst gleichzeitig dieZerfaellekurzlebiger und langlebiger Kaonen in zwei geladene undneutralePionen. Der Parameter der direkten CP Verletzung wird durchdasDoppelverhaeltnis der vier Zerfallsraten bestimmt. DasExperiment unddie Analyse sind so gestaltet, dass sich systematischeEffekte imDoppelverhaeltnis der Zerfallsraten prinzipiell aufheben.DieBestimmung unvermeidlicher systematischer Abweichungen nimmteinenHauptteil der Dissertation ein. Fuer diese Analyse wurdendie Datender ersten Strahlzeit 1997 verwendet. Das Ergebnis dieserAnalysefuer den Parameter der direkten CP Verletzung ist (18.3 +/-4.6 +/- 5.8) * 10E-4.

The topological trigger system of the TOF detector for the ALICE experiment at the LHC

The ALICE experiment at the LHC has been designed to cope with the experimental conditions and observables of a Quark Gluon Plasma reaction. One of the main assets of the ALICE experiment with respect to the other LHC experiments is the particle identification. The large Time-Of-Flight (TOF) detector is the main particle identification detector of the ALICE experiment. The overall time resolution, better that 80 ps, allows the particle identification over a large momentum range (up to 2.5 GeV/c for pi/K and 4 GeV/c for K/p). The TOF makes use of the Multi-gap Resistive Plate Chamber (MRPC), a detector with high efficiency, fast response and intrinsic time resoltion better than 40 ps. The TOF detector embeds a highly-segmented trigger system that exploits the fast rise time and the relatively low noise of the MRPC strips, in order to identify several event topologies. This work aims to provide detailed description of the TOF trigger system. The results achieved in the 2009 cosmic-ray run at CERN are presented to show the performances and readiness of TOF trigger system. The proposed trigger configuration for the proton-proton and Pb-Pb beams are detailed as well with estimates of the efficiencies and purity samples.

Optische Spektroskopie an Fermium (Z=100)

Im Rahmen der vorliegenden Arbeit wurde erstmals Laser-Atomspektroskopie an einem Element durchgeführt, für das bisher keine atomaren Niveaus bekannt waren. Die Experimente wurden am Element Fermium mit der Ordnungszahl Z=100 mit der Resonanzionisationsspektroskopie (RIS) in einer Puffergaszelle durchgeführt. Verwendet wurde das Isotop 255Fm mit einer Halbwertszeit von 20.1 h, das im Hochflusskernreaktor des ORNL, Oak Ridge, USA, hergestellt wurde. Die von einem elektrochemischen Filament in das Argon-Puffergas bei einer Temperatur von 960(20)°C abgedampften Fm-Atome wurden mit Lasern in einem Zweistufenprozess resonant ionisiert. Dazu wurde das Licht eines Excimerlaser gepumpten Farbstofflasers für den ersten Anregungsschritt um die Wellenlänge 400 nm durchgestimmt. Ein Teil des Excimer (XeF) Laser Pumplichtes mit den Wellenlänge 351/353 nm wurde für die nicht-resonante Ionisation verwendet. Die Ionen wurden mit Hilfe elektrischer Felder aus der optischen Zelle extrahiert und nach einem Quadrupol Massenfilter mit einem Channeltron-Detektor massenselektiv nachgewiesen. Trotz der geringen Probenmenge von 2.7 x 10^10 eingesetzten Atomen wurden zwei atomare Resonanzen bei Energien von 25099.8(2) cm-1 und 25111.8(2) cm-1 gefunden und das Sättigungsverhalten dieser Linien gemessen. Es wurde ein theoretisches Modell entwickelt, dass sowohl das spektrale Profil der sättigungsverbreiterten Linien als auch die Sättigungskurven beschreibt. Durch Anpassung an die Messdaten konnten die partiellen Übergangsraten in den 3H6 Grundzustand Aki=3.6(7) x 10^6/s und Aki=3.6(6) x 10^6/s bestimmt werden. Der Vergleich der Niveauenergien und Übergangsraten mit Multikonfigurations Dirac-Fock Rechnungen legt die spektroskopische Klassifizierung der beobachteten Niveaus als 5f12 7s7p 5I6 und 5G6 Terme nahe. Weiterhin wurde ein Übergang bei 25740 cm-1 gefunden, der aufgrund der beobachteten Linienbreite von 1000 GHz als Rydbergzustand Zustand mit der Niveauenergie 51480 cm-1 interpretiert wurde und über einen Zweiphotonen Prozess angeregt werden kann. Basierend auf dieser Annahme wurde die Obergrenze für die Ionisationsenergie IP = 52140 cm-1 = 6.5 eV abgeschätzt. In den Messungen wurden Verschiebungen in den Zeitverteilungsspektren zwischen den mono-atomaren Ionen Fm+ und Cf+ und dem Molekül-Ion UO+ festgestellt und auf Driftzeitunterschiede im elektrischen Feld der gasgefüllten optischen Zelle zurückgeführt. Unter einfachen Modellannahmen wurde daraus auf die relativen Unterschiede Delta_r(Fm+,Cf+)/r(Cf+) ˜ -0.2 % und Delta_r(UO+,Cf+)/r(Cf+) ˜ 20 % in den Ionenradien geschlossen. Über die Bestimmung der Abnahme der Fm-a Aktivität des Filamentes auf der einen Seite und die Messung der Resonanzzählrate auf der anderen Seite, wurde die Nachweiseffizienz der Apparatur zu 4.5(3) x 10^-4 bestimmt. Die Nachweisapparatur wurde mit dem Ziel weiterentwickelt, Laserspektroskopie am Isotop 251Fm durchzuführen, das über die Reaktion 249Cf(a,2n)251Fm direkt in der optischen Zelle erzeugt werden soll. Das Verfahren wurde am chemischen Homolog Erbium getestet. Dabei wurde das Isotop 163Er über die Reaktion 161Dy(a,2n)163Er erzeugt und nach Resonanzionisation nachgewiesen. Die Nachweiseffizienz der Methode wurde zu 1 x 10^-4 bestimmt.

Luminosity measurements with the LUCID detector in the ATLAS experiment

La misura della luminosità è un obiettivo importante per tutta la fisica del modello standard e per la scoperta di nuova fisica, poiché è legata alla sezione d'urto (σ) e al rate di produzione (R) di un determinato processo dalla relazione L = R*σ. Nell'eserimento ATLAS a LHC è installato un monitor di luminosità dedicato chiamato LUCID (Luminosity measurements Using Cherenkov Integrating Detector). Grazie ai dati acquisiti durante il 2010 la valutazione off-line delle performances del LUCID e l'implementazione di controlli on-line sulla qualità dei dati raccolti è stata possibile. I dati reali sono stati confrontati con i dati Monte Carlo e le simulazioni sono state opportunamente aggiustate per ottimizzare l'accordo tra i due. La calibrazione della luminosità relativa che permette di ottenere una valutazione della luminosità assoluta è stata possibile grazie ai cosiddetti Van der Meer scan, grazie ai quale è stata ottenuta una precisione dell'11%. L'analisi della fisica del decadimento della Z è in tuttora in corso per ottenere tramite il rate a cui avviene il processo una normalizzazione della luminosità con una precisione migliore del 5%.

Entwicklung einer Fokalebenen-Driftkammer für niederenergetische Pionen und experimentelle Bestimmung einer inversen Transfermatrix für das Short-Orbit-Spektrometer

Die Drei-Spektrometer-Anlage am Mainzer Institut für Kernphysik wurde um ein zusätzliches Spektrometer ergänzt, welches sich durch seine kurze Baulänge auszeichnet und deshalb Short-Orbit-Spektrometer (SOS) genannt wird. Beim nominellen Abstand des SOS vom Target (66 cm) legen die nachzuweisenden Teilchen zwischen Reaktionsort und Detektor eine mittlere Bahnlänge von 165 cm zurück. Für die schwellennahe Pionproduktion erhöht sich dadurch im Vergleich zu den großen Spektrometern die Überlebenswahrscheinlichkeit geladener Pionen mit Impuls 100 MeV/c von 15% auf 73%. Demzufolge verringert sich der systematische Fehler ("Myon-Kontamination"), etwa bei der geplanten Messung der schwachen Formfaktoren G_A(Q²) und G_P(Q²), signifikant. Den Schwerpunkt der vorliegenden Arbeit bildet die Driftkammer des SOS. Ihre niedrige Massenbelegung (0,03% X_0) zur Reduzierung der Kleinwinkelstreuung ist auf den Nachweis niederenergetischer Pionen hin optimiert. Aufgrund der neuartigen Geometrie des Detektors musste eine eigene Software zur Spurrekonstruktion, Effizienzbestimmung etc. entwickelt werden. Eine komfortable Möglichkeit zur Eichung der Driftweg-Driftzeit-Relation, die durch kubische Splines dargestellt wird, wurde implementiert. Das Auflösungsvermögen des Spurdetektors liegt in der dispersiven Ebene bei 76 µm für die Orts- und 0,23° für die Winkelkoordinate (wahrscheinlichster Fehler) sowie entsprechend in der nicht-dispersiven Ebene bei 110 µm bzw. 0,29°. Zur Rückrechnung der Detektorkoordinaten auf den Reaktionsort wurde die inverse Transfermatrix des Spektrometers bestimmt. Hierzu wurden an Protonen im ¹²C-Kern quasielastisch gestreute Elektronen verwendet, deren Startwinkel durch einen Lochkollimator definiert wurden. Daraus ergeben sich experimentelle Werte für die mittlere Winkelauflösung am Target von sigma_phi = 1,3 mrad bzw. sigma_theta = 10,6 mrad. Da die Impulseichung des SOS nur mittels quasielastischer Streuung (Zweiarmexperiment) durchgeführt werden kann, muss man den Beitrag des Protonarms zur Breite des Piks der fehlenden Masse in einer Monte-Carlo-Simulation abschätzen und herausfalten. Zunächst lässt sich nur abschätzen, dass die Impulsauflösung sicher besser als 1% ist.

Modeling, design and experimental characterization of Micro-Electro-Mechanical-Systems for gas chromatographic applications

Design parameters, process flows, electro-thermal-fluidic simulations and experimental characterizations of Micro-Electro-Mechanical-Systems (MEMS) suited for gas-chromatographic (GC) applications are presented and thoroughly described in this thesis, whose topic belongs to the research activities the Institute for Microelectronics and Microsystems (IMM)-Bologna is involved since several years, i.e. the development of micro-systems for chemical analysis, based on silicon micro-machining techniques and able to perform analysis of complex gaseous mixtures, especially in the field of environmental monitoring. In this regard, attention has been focused on the development of micro-fabricated devices to be employed in a portable mini-GC system for the analysis of aromatic Volatile Organic Compounds (VOC) like Benzene, Toluene, Ethyl-benzene and Xylene (BTEX), i.e. chemical compounds which can significantly affect environment and human health because of their demonstrated carcinogenicity (benzene) or toxicity (toluene, xylene) even at parts per billion (ppb) concentrations. The most significant results achieved through the laboratory functional characterization of the mini-GC system have been reported, together with in-field analysis results carried out in a station of the Bologna air monitoring network and compared with those provided by a commercial GC system. The development of more advanced prototypes of micro-fabricated devices specifically suited for FAST-GC have been also presented (silicon capillary columns, Ultra-Low-Power (ULP) Metal OXide (MOX) sensor, Thermal Conductivity Detector (TCD)), together with the technological processes for their fabrication. The experimentally demonstrated very high sensitivity of ULP-MOX sensors to VOCs, coupled with the extremely low power consumption, makes the developed ULP-MOX sensor the most performing metal oxide sensor reported up to now in literature, while preliminary test results proved that the developed silicon capillary columns are capable of performances comparable to those of the best fused silica capillary columns. Finally, the development and the validation of a coupled electro-thermal Finite Element Model suited for both steady-state and transient analysis of the micro-devices has been described, and subsequently implemented with a fluidic part to investigate devices behaviour in presence of a gas flowing with certain volumetric flow rates.

The incomplete ionization of substitutional dopants in Silicon Carbide

This thesis analyzes theoretically and computationally the phenomenon of partial ionization of the substitutional dopants in Silicon Carbide at thermal equilibrium. It is based on the solution of the charge neutrality equation and takes into account the following phenomena: several energy levels in the bandgap; Fermi-Dirac statistics for free carriers; screening effects on the dopant ionization energies; the formation of impurity bands. A self-consistent model and a corresponding simulation software have been realized. A preliminary comparison of our calculations with existing experimental results is carried out.

Design and Setup of a New HPGe Detector Based Body Counter Capable of Detecting Also Low Energy Photon Emitters

The present work describes the development of a new body-counter system based on HPGe detectors and installed at IVM of KIT. The goal, achieved, was the improvement of the ability to detect internal contaminations in the human body, especially the ones concerning low-energy emitters and multiple nuclides. The development of the system started with the characterisation of detectors purchased for this specific task, with the optimisation of the different desired measurement configurations following and ending with the installation and check of the results. A new software has been developed to handle the new detectors.

Measurement of the atmospheric muon charge ratio with the OPERA detector

The atmospheric muon charge ratio, defined as the number of positive over negative charged muons, is an interesting quantity for the study of high energy hadronic interactions in atmosphere and the nature of the primary cosmic rays. The measurement of the charge ratio in the TeV muon energy range allows to study the hadronic interactions in kinematic regions not yet explored at accelerators. The OPERA experiment is a hybrid electronic detector/emulsion apparatus, located in the underground Gran Sasso Laboratory, at an average depth of 3800 meters water equivalent (m.w.e.). OPERA is the first large magnetized detector that can measure the muon charge ratio at the LNGS depth, with a wide acceptance for cosmic ray muons coming from above. In this thesis, the muon charge ratio is measured using the spectrometers of the OPERA detector in the highest energy region. The charge ratio was computed separately for single and for multiple muon events, in order to select different primary cosmic ray samples in energy and composition. The measurement as a function of the surface muon energy is used to infer parameters characterizing the particle production in atmosphere, that will be used to constrain Monte Carlo predictions. Finally, the experimental results are interpreted in terms of cosmic ray and particle physics models.

Silicon-containing block copolymers with well-defined, branched architectures

In the past decade, block copolymers (BCPs) have attracted increasing scientific and technological interest because of their inherent capability to spontaneously self-assemble into ordered arrays of nanostructures. The importance of nanostructures in a number of applications has fostered the need for well-defined, complex macromolecular architectures. In this thesis, the influence of macromolecular architecture on the bulk morphologies of novel linear-hyperbranched and linear brush-like diblock copolymer structure is investigated. An innovative, generally applicable strategy for the preparation of these defined diblock copolymers, consisting of linear polystyrene and branched polycarbosilane blocks, is demonstrated. Furthermore, complete characterization and solid-state morphological studies are provided. Finally, the concept is extended to linear-hyperbrached and linear brush-like polyalkoxysilanes. A shift of the classical phase boundaries to higher PS weight fractions as well as the appearance of new morphologies confirms the dramatic effect that polymer topology has on the morphology of BCPs.

Identified primary hadron spectra with the TOF detector of the ALICE experiment at LHC

In this thesis the analysis to reconstruct the transverse momentum p_{t} spectra for pions, kaons and protons identified with the TOF detector of the ALICE experiment in pp Minimum Bias collisions at $\sqrt{s}=7$ TeV was reported. After a detailed description of all the parameters which influence the TOF PID performance (time resolution, calibration, alignment, matching efficiency, time-zero of the event) the method used to identify the particles, the unfolding procedure, was discussed. With this method, thanks also to the excellent TOF performance, the pion and kaon spectra can be reconstructed in the 0.5detectors and techniques to extend the identified spectra to a wider $p_{t}$ range was reported, showing an agreement within 6\%.

Existence of solutions and asymtptotic limits of the Euler-Poisson and the quantum drift-diffusion systems

My work concerns two different systems of equations used in the mathematical modeling of semiconductors and plasmas: the Euler-Poisson system and the quantum drift-diffusion system. The first is given by the Euler equations for the conservation of mass and momentum, with a Poisson equation for the electrostatic potential. The second one takes into account the physical effects due to the smallness of the devices (quantum effects). It is a simple extension of the classical drift-diffusion model which consists of two continuity equations for the charge densities, with a Poisson equation for the electrostatic potential. Using an asymptotic expansion method, we study (in the steady-state case for a potential flow) the limit to zero of the three physical parameters which arise in the Euler-Poisson system: the electron mass, the relaxation time and the Debye length. For each limit, we prove the existence and uniqueness of profiles to the asymptotic expansion and some error estimates. For a vanishing electron mass or a vanishing relaxation time, this method gives us a new approach in the convergence of the Euler-Poisson system to the incompressible Euler equations. For a vanishing Debye length (also called quasineutral limit), we obtain a new approach in the existence of solutions when boundary layers can appear (i.e. when no compatibility condition is assumed). Moreover, using an iterative method, and a finite volume scheme or a penalized mixed finite volume scheme, we numerically show the smallness condition on the electron mass needed in the existence of solutions to the system, condition which has already been shown in the literature. In the quantum drift-diffusion model for the transient bipolar case in one-space dimension, we show, by using a time discretization and energy estimates, the existence of solutions (for a general doping profile). We also prove rigorously the quasineutral limit (for a vanishing doping profile). Finally, using a new time discretization and an algorithmic construction of entropies, we prove some regularity properties for the solutions of the equation obtained in the quasineutral limit (for a vanishing pressure). This new regularity permits us to prove the positivity of solutions to this equation for at least times large enough.

Advanced Numerical Simulation of Silicon-Based Solar Cells

Photovoltaic (PV) conversion is the direct production of electrical energy from sun without involving the emission of polluting substances. In order to be competitive with other energy sources, cost of the PV technology must be reduced ensuring adequate conversion efficiencies. These goals have motivated the interest of researchers in investigating advanced designs of crystalline silicon solar (c-Si) cells. Since lowering the cost of PV devices involves the reduction of the volume of semiconductor, an effective light trapping strategy aimed at increasing the photon absorption is required. Modeling of solar cells by electro-optical numerical simulation is helpful to predict the performance of future generations devices exhibiting advanced light-trapping schemes and to provide new and more specific guidelines to industry. The approaches to optical simulation commonly adopted for c-Si solar cells may lead to inaccurate results in case of thin film and nano-stuctured solar cells. On the other hand, rigorous solvers of Maxwell equations are really cpu- and memory-intensive. Recently, in optical simulation of solar cells, the RCWA method has gained relevance, providing a good trade-off between accuracy and computational resources requirement. This thesis is a contribution to the numerical simulation of advanced silicon solar cells by means of a state-of-the-art numerical 2-D/3-D device simulator, that has been successfully applied to the simulation of selective emitter and the rear point contact solar cells, for which the multi-dimensionality of the transport model is required in order to properly account for all physical competing mechanisms. In the second part of the thesis, the optical problems is discussed. Two novel and computationally efficient RCWA implementations for 2-D simulation domains as well as a third RCWA for 3-D structures based on an eigenvalues calculation approach have been presented. The proposed simulators have been validated in terms of accuracy, numerical convergence, computation time and correctness of results.

Study of the forward photons productions in pp collisions at sqrt{s} = 7 TeV with the ZDC detector of the ATLAS experiment

The Zero Degree Calorimeter (ZDC) of the ATLAS experiment at CERN is placed in the TAN of the LHC collider, covering the pseudorapidity region higher than 8.3. It is composed by 2 calorimeters, each one longitudinally segmented in 4 modules, located at 140 m from the IP exactly on the beam axis. The ZDC can detect neutral particles during pp collisions and it is a tool for diffractive physics. Here we present results on the forward photon energy distribution obtained using p-p collision data at sqrt{s} = 7 TeV. First the pi0 reconstruction will be used for the detector calibration with photons, then we will show results on the forward photon energy distribution in p-p collisions and the same distribution, but obtained using MC generators. Finally a comparison between data and MC will be shown.