High precision tools for slepton pair production processes at hadron colliders

In this thesis, we develop high precision tools for the simulation of slepton pair production processes at hadron colliders and apply them to phenomenological studies at the LHC. Our approach is based on the POWHEG method for the matching of next-to-leading order results in perturbation theory to parton showers. We calculate matrix elements for slepton pair production and for the production of a slepton pair in association with a jet perturbatively at next-to-leading order in supersymmetric quantum chromodynamics. Both processes are subsequently implemented in the POWHEG BOX, a publicly available software tool that contains general parts of the POWHEG matching scheme. We investigate phenomenological consequences of our calculations in several setups that respect experimental exclusion limits for supersymmetric particles and provide precise predictions for slepton signatures at the LHC. The inclusion of QCD emissions in the partonic matrix elements allows for an accurate description of hard jets. Interfacing our codes to the multi-purpose Monte-Carlo event generator PYTHIA, we simulate parton showers and slepton decays in fully exclusive events. Advanced kinematical variables and specific search strategies are examined as means for slepton discovery in experimentally challenging setups.

Production, radiochemical separation and chemical coupling of radioactive arsenic isotopes to synthesize radiopharmaceuticals for molecular imaging

Noninvasive molecular-imaging technologies are playing a keyrole in drug discovery, development and delivery. Positron Emission Tomography (PET) is such a molecular imaging technology and a powerful tool for the observation of various diseases. However, it is limited by the availability of agents with high selectivity to the target and a physical half-life of the used positron emitting nuclide which matches the biological half-life of the observed process. For the long lasting enrichment of antibodies in tumor tissue few suitable isotopes for PET imaging are currently available. The element arsenic provides a range of isotopes, which could be used for diagnosis and also for endoradiotherapy. This work describes the development of radiochemical separation procedures to separate arsenic isotopes in no-carrier-added (nca) purity from reactor or cyclotron irradiated targets, the development and evaluation of a labeling chemistry to attach these separated arsenic isotopes to monoclonal antibodies, the in vitro and in vivo evaluation of antibodies labeled with radioactive arsenic isotopes and the molecular imaging using small animal PET.

Development of an experiment for ultrahigh-precision g-factor

Die vorliegende Arbeit befasst sich mit der Entwicklung und dem Aufbau eines Experiments zur hochpräzisen Bestimmung des g-Faktors gebundener Elektronen in hochgeladenen Ionen. Der g-Faktor eines Teilchens ist eine dimensionslose Konstante, die die Stärke der Wechselwirkung mit einem magnetischen Feld beschreibt. Im Falle eines an ein hochgeladenes Ion gebundenen Elektrons, dient es als einer der genausten Tests der Quantenelektrodynamik gebundener Zustande (BS-QED). Die Messung wird in einem dreifach Penning-Fallen System durchgeführt und basiert auf dem kontinuierlichen Stern-Gerlach-Effekt. Der erste Teil dieser Arbeit gibt den aktuellen Wissensstand über magnetische Momente wieder. Der hier gewählte experimentelle Aufbau wird begründet. Anschließend werden die experimentellen Anforderungen und die verwendeten Messtechniken erläutert. Das Ladungsbrüten der Ionen - einer der wichtigsten Aufgaben dieser Arbeit - ist dargestellt. Seine Realisierung basiert auf einer Feld-Emissions-Spitzen-Anordnung, die die Messung des Wirkungsquerschnitts für Elektronenstoßionisation ermöglicht. Der letzte Teil der Arbeit widmet sich der Entwicklung und dem Aufbau des Penning-Fallen Systems, sowie der Implementierung des Nachweisprozesses. Gegenwärtig ist der Aufbau zur Erzeugung hochgeladener Ionen und der dazugehörigen Messung des g-Faktors abgeschlossen, einschließlich des Steuerprogramms für die erste Datennahme. Die Ionenerzeugung und das Ladungsbrüten werden die nächsten Schritte sein.

Determination of the gluon polarisation from open charm production at COMPASS

One of the main goals of the COMPASS experiment at CERN is the determination of the gluon polarisation in the nucleon. It is determined from spin asymmetries in the scattering of 160 GeV/c polarised muons on a polarised LiD target. The gluon polarisation is accessed by the selection of photon-gluon fusion (PGF) events. The PGF-process can be tagged through hadrons with high transverse momenta or through charmed hadrons in the final state. The advantage of the open charm channel is that, in leading order, the PGF-process is the only process for charm production, thus no physical background contributes to the selected data sample. This thesis presents a measurement of the gluon polarisation from the COMPASS data taken in the years 2002-2004. In the analysis, charm production is tagged through a reconstructed D0-meson decaying in $D^{0}-> K^{-}pi^{+}$ (and charge conjugates). The reconstruction is done on a combinatorial basis. The background of wrong track pairs is reduced using kinematic cuts to the reconstructed D0-candidate and the information on particle identification from the Ring Imaging Cerenkov counter. In addition, the event sample is separated into D0-candidates, where a soft pion from the decay of the D*-meson to a D0-meson, is found, and the D0-candidates without this tag. Due to the small mass difference between D*-meson and D0-meson the signal purity of the D*-tagged sample is about 7 times higher than in the untagged sample. The gluon polarisation is measured from the event asymmetries for the for the different spin configurations of the COMPASS target. To improve the statistical precision of the final results, the events in the final sample are weighted. This method results in an average value of the gluon polarisation in the x-range covered by the data. For the COMPASS data from 2002-2004, the resulting value of the gluon polarisation is $=-0.47+-0.44 (stat)+-0.15(syst.)$. The result is statistically compatible with the existing measurements of $$ in the high-pT channel. Compared to these, the open charm measurement has the advantage of a considerably smaller model dependence.

The construction of TRIGA-TRAP and direct high-precision Penning trap mass measurements on rare-earth elements and americium

Nuclear masses are an important quantity to study nuclear structure since they reflect the sum of all nucleonic interactions. Many experimental possibilities exist to precisely measure masses, out of which the Penning trap is the tool to reach the highest precision. Moreover, absolute mass measurements can be performed using carbon, the atomic-mass standard, as a reference. The new double-Penning trap mass spectrometer TRIGA-TRAP has been installed and commissioned within this thesis work, which is the very first experimental setup of this kind located at a nuclear reactor. New technical developments have been carried out such as a reliable non-resonant laser ablation ion source for the production of carbon cluster ions and are still continued, like a non-destructive ion detection technique for single-ion measurements. Neutron-rich fission products will be available by the reactor that are important for nuclear astrophysics, especially the r-process. Prior to the on-line coupling to the reactor, TRIGA-TRAP already performed off-line mass measurements on stable and long-lived isotopes and will continue this program. The main focus within this thesis was on certain rare-earth nuclides in the well-established region of deformation around N~90. Another field of interest are mass measurements on actinoids to test mass models and to provide direct links to the mass standard. Within this thesis, the mass of 241-Am could be measured directly for the first time.

Feasibility study of performing high precision gamma spectroscopy of lambda lambda hypernuclei in the PANDA experiment

Hypernuclear physics is currently attracting renewed interest, due tornthe important role of hypernuclei spectroscopy rn(hyperon-hyperon and hyperon-nucleon interactions) rnas a unique toolrnto describe the baryon-baryon interactions in a unified way and to rnunderstand the origin of their short-range.rnrnHypernuclear research will be one of the main topics addressed by the {sc PANDA} experimentrnat the planned Facility for Antiproton and Ion Research {sc FAIR}.rnThanks to the use of stored $overline{p}$ beams, copiousrnproduction of double $Lambda$ hypernuclei is expected at thern{sc PANDA} experiment, which will enable high precision $gamma$rnspectroscopy of such nuclei for the first time.rnAt {sc PANDA} excited states of $Xi^-$ hypernuclei will be usedrnas a basis for the formation of double $Lambda$ hypernuclei.rnFor their detection, a devoted hypernuclear detector setup is planned. This setup consists ofrna primary nuclear target for the production of $Xi^{-}+overline{Xi}$ pairs, a secondary active targetrnfor the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform $gamma$ spectroscopy.rnrnIn the present work, the feasibility of performing high precision $gamma$rnspectroscopy of double $Lambda$ hypernuclei at the {sc PANDA} experiment has been studiedrnby means of a Monte Carlo simulation. For this issue, the designing and simulation of the devoted detector setup as well as of the mechanism to produce double $Lambda$ hypernuclei have been optimizedrntogether with the performance of the whole system. rnIn addition, the production yields of double hypernuclei in excitedrnparticle stable states have been evaluated within a statistical decay model.rnrnA strategy for the unique assignment of various newly observed $gamma$-transitions rnto specific double hypernuclei has been successfully implemented by combining the predicted energy spectra rnof each target with the measurement of two pion momenta from the subsequent weak decays of a double hypernucleus.rn% Indeed, based on these Monte Carlo simulation, the analysis of the statistical decay of $^{13}_{Lambda{}Lambda}$B has been performed. rn% As result, three $gamma$-transitions associated to the double hypernuclei $^{11}_{Lambda{}Lambda}$Bern% and to the single hyperfragments $^{4}_{Lambda}$H and $^{9}_{Lambda}$Be, have been well identified.rnrnFor the background handling a method based on time measurement has also been implemented.rnHowever, the percentage of tagged events related to the production of $Xi^{-}+overline{Xi}$ pairs, variesrnbetween 20% and 30% of the total number of produced events of this type. As a consequence, further considerations have to be made to increase the tagging efficiency by a factor of 2.rnrnThe contribution of the background reactions to the radiation damage on the germanium detectorsrnhas also been studied within the simulation. Additionally, a test to check the degradation of the energyrnresolution of the germanium detectors in the presence of a magnetic field has also been performed.rnNo significant degradation of the energy resolution or in the electronics was observed. A correlationrnbetween rise time and the pulse shape has been used to correct the measured energy. rnrnBased on the present results, one can say that the performance of $gamma$ spectroscopy of double $Lambda$ hypernuclei at the {sc PANDA} experiment seems feasible.rnA further improvement of the statistics is needed for the background rejection studies. Moreover, a more realistic layout of the hypernuclear detectors has been suggested using the results of these studies to accomplish a better balance between the physical and the technical requirements.rn

Electroweak precision observables and effective four-fermion interactions in warped extra dimensions

In this thesis, we study the phenomenology of selected observables in the context of the Randall-Sundrum scenario of a compactified warpedrnextra dimension. Gauge and matter fields are assumed to live in the whole five-dimensional space-time, while the Higgs sector is rnlocalized on the infrared boundary. An effective four-dimensional description is obtained via Kaluza-Klein decomposition of the five dimensionalrnquantum fields. The symmetry breaking effects due to the Higgs sector are treated exactly, and the decomposition of the theory is performedrnin a covariant way. We develop a formalism, which allows for a straight-forward generalization to scenarios with an extended gauge group comparedrnto the Standard Model of elementary particle physics. As an application, we study the so-called custodial Randall-Sundrum model and compare the resultsrnto that of the original formulation. rnWe present predictions for electroweak precision observables, the Higgs production cross section at the LHC, the forward-backward asymmetryrnin top-antitop production at the Tevatron, as well as the width difference, the CP-violating phase, and the semileptonic CP asymmetry in B_s decays.

Warped extra dimensions: flavor, precision tests and Higgs physics

In this thesis, the phenomenology of the Randall-Sundrum setup is investigated. In this context models with and without an enlarged SU(2)_L x SU(2)_R x U(1)_X x P_{LR} gauge symmetry, which removes corrections to the T parameter and to the Z b_L \bar b_L coupling, are compared with each other. The Kaluza-Klein decomposition is formulated within the mass basis, which allows for a clear understanding of various model-specific features. A complete discussion of tree-level flavor-changing effects is presented. Exact expressions for five dimensional propagators are derived, including Yukawa interactions that mediate flavor-off-diagonal transitions. The symmetry that reduces the corrections to the left-handed Z b \bar b coupling is analyzed in detail. In the literature, Randall-Sundrum models have been used to address the measured anomaly in the t \bar t forward-backward asymmetry. However, it will be shown that this is not possible within a natural approach to flavor. The rare decays t \to cZ and t \to ch are investigated, where in particular the latter could be observed at the LHC. A calculation of \Gamma_{12}^{B_s} in the presence of new physics is presented. It is shown that the Randall-Sundrum setup allows for an improved agreement with measurements of A_{SL}^s, S_{\psi\phi}, and \Delta\Gamma_s. For the first time, a complete one-loop calculation of all relevant Higgs-boson production and decay channels in the custodial Randall-Sundrum setup is performed, revealing a sensitivity to large new-physics scales at the LHC.

Measurement of the pair production of b-jets in proton-proton collisions at root out s = 7 TeV with the ATLAS detector

In hadronischen Kollisionen entstehen bei einem Großteil der Ereignisse mit einem hohen Impulsübertrag Paare aus hochenergetischen Jets. Deren Produktion und Eigenschaften können mit hoher Genauigkeit durch die Störungstheorie in der Quantenchromodynamik (QCD) vorhergesagt werden. Die Produktion von \textit{bottom}-Quarks in solchen Kollisionen kann als Maßstab genutzt werden, um die Vorhersagen der QCD zu testen, da diese Quarks die Dynamik des Produktionsprozesses bei Skalen wieder spiegelt, in der eine Störungsrechnung ohne Einschränkungen möglich ist. Auf Grund der hohen Masse von Teilchen, die ein \textit{bottom}-Quark enthalten, erhält der gemessene, hadronische Zustand den größten Teil der Information von dem Produktionsprozess der Quarks. Weil sie eine große Produktionsrate besitzen, spielen sie und ihre Zerfallsprodukte eine wichtige Rolle als Untergrund in vielen Analysen, insbesondere in Suchen nach neuer Physik. In ihrer herausragenden Stellung in der dritten Quark-Generation könnten sich vermehrt Zeichen im Vergleich zu den leichteren Quarks für neue Phänomene zeigen. Daher ist die Untersuchung des Verhältnisses zwischen der Produktion von Jets, die solche \textit{bottom}-Quarks enthalten, auch bekannt als $b$-Jets, und aller nachgewiesener Jets ein wichtiger Indikator für neue massive Objekte. In dieser Arbeit werden die Produktionsrate und die Korrelationen von Paaren aus $b$-Jets bestimmt und nach ersten Hinweisen eines neuen massiven Teilchens, das bisher nicht im Standard-Modell enthalten ist, in dem invarianten Massenspektrum der $b$-Jets gesucht. Am Large Hadron Collider (LHC) kollidieren zwei Protonenstrahlen bei einer Schwerpunktsenergie von $\sqrt s = 7$ TeV, und es werden viele solcher Paare aus $b$-Jets produziert. Diese Analyse benutzt die aufgezeichneten Kollisionen des ATLAS-Detektors. Die integrierte Luminosität der verwendbaren Daten beläuft sich auf 34~pb$^{-1}$. $b$-Jets werden mit Hilfe ihrer langen Lebensdauer und den rekonstruierten, geladenen Zerfallsprodukten identifiziert. Für diese Analyse müssen insbesondere die Unterschiede im Verhalten von Jets, die aus leichten Objekten wie Gluonen und leichten Quarks hervorgehen, zu diesen $b$-Jets beachtet werden. Die Energieskala dieser $b$-Jets wird untersucht und die zusätzlichen Unsicherheit in der Energiemessung der Jets bestimmt. Effekte bei der Jet-Rekonstruktion im Detektor, die einzigartig für $b$-Jets sind, werden studiert, um letztlich diese Messung unabhängig vom Detektor und auf Niveau der Hadronen auswerten zu können. Hiernach wird die Messung zu Vorhersagen auf nächst-zu-führender Ordnung verglichen. Dabei stellt sich heraus, dass die Vorhersagen in Übereinstimmung zu den aufgenommenen Daten sind. Daraus lässt sich schließen, dass der zugrunde liegende Produktionsmechanismus auch in diesem neu erschlossenen Energiebereich am LHC gültig ist. Jedoch werden auch erste Hinweise auf Mängel in der Beschreibung der Eigenschaften dieser Ereignisse gefunden. Weiterhin können keine Anhaltspunkte für eine neue Resonanz, die in Paare aus $b$-Jets zerfällt, in dem invarianten Massenspektrum bis etwa 1.7~TeV gefunden werden. Für das Auftreten einer solchen Resonanz mit einer Gauß-förmigen Massenverteilung werden modell-unabhängige Grenzen berechnet.

Production of antihydrogen via double charge exchange

Spectroscopy of the 1S-2S transition of antihydrogen confined in a neutral atom trap and comparison with the equivalent spectral line in hydrogen will provide an accurate test of CPT symmetry and the first one in a mixed baryon-lepton system. Also, with neutral antihydrogen atoms, the gravitational interaction between matter and antimatter can be tested unperturbed by the much stronger Coulomb forces.rnAntihydrogen is regularly produced at CERN's Antiproton Decelerator by three-body-recombination (TBR) of one antiproton and two positrons. The method requires injecting antiprotons into a cloud of positrons, which raises the average temperature of the antihydrogen atoms produced way above the typical 0.5 K trap depths of neutral atom traps. Therefore only very few antihydrogen atoms can be confined at a time. Precision measurements, like laser spectroscopy, will greatly benefit from larger numbers of simultaneously trapped antihydrogen atoms.rnTherefore, the ATRAP collaboration developed a different production method that has the potential to create much larger numbers of cold, trappable antihydrogen atoms. Positrons and antiprotons are stored and cooled in a Penning trap in close proximity. Laser excited cesium atoms collide with the positrons, forming Rydberg positronium, a bound state of an electron and a positron. The positronium atoms are no longer confined by the electric potentials of the Penning trap and some drift into the neighboring cloud of antiprotons where, in a second charge exchange collision, they form antihydrogen. The antiprotons remain at rest during the entire process, so much larger numbers of trappable antihydrogen atoms can be produced. Laser excitation is necessary to increase the efficiency of the process since the cross sections for charge-exchange collisions scale with the fourth power of the principal quantum number n.rnThis method, named double charge-exchange, was demonstrated by ATRAP in 2004. Since then, ATRAP constructed a new combined Penning Ioffe trap and a new laser system. The goal of this thesis was to implement the double charge-exchange method in this new apparatus and increase the number of antihydrogen atoms produced.rnCompared to our previous experiment, we could raise the numbers of positronium and antihydrogen atoms produced by two orders of magnitude. Most of this gain is due to the larger positron and antiproton plasmas available by now, but we could also achieve significant improvements in the efficiencies of the individual steps. We therefore showed that the double charge-exchange can produce comparable numbers of antihydrogen as the TBR method, but the fraction of cold, trappable atoms is expected to be much higher. Therefore this work is an important step towards precision measurements with trapped antihydrogen atoms.