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.In dieser Doktorarbeit entwickeln wir Hochpräzisionswerkzeuge für die Simulation der Paarproduktion von Sleptonen in hadronischen Kollisionsprozessen an Teilchenbeschleunigern und verwenden sie für phänomenologische Untersuchungen am LHC. Unser Vorgehen basiert auf der POWHEG Methode für die konsistente Kombination von störungstheoretischen Resultaten in nächstführender Ordnung mit Partonschauern. Wir berechnen die Matrixelemente für die Paarproduktion von Sleptonen sowie für die Produktion eines Sleptonpaares in Assoziation mit einem Jet gemäß störungstheoretischer Methoden der supersymmetrischen Quantenchromodynamik in nächstführender Ordnung. Beide Prozesse implementieren wir anschließend in der POWHEG BOX, einem öffentlich verfügbaren Computerprogramm, das allgemeine Bestandteile des POWHEG Verfahrens enthält. Wir untersuchen phänomenologische Konsequenzen unserer Berechnungen in mehreren supersymmetrischen Massenkonfigurationen unter Beachtung experimenteller Ausschlussgrenzen und treffen präzise Vorhersagen für Sleptonsignaturen am LHC. Eine genaue Beschreibung harter Jets erfolgt durch die Berücksichtigung von QCD-Emissionen in den partonischen Matrixelementen. Partonschauer und Sleptonzerfälle simulieren wir in vollständig exklusiven Kollisionsereignissen durch die Anbindung unserer Implementierungen an das Monte-Carlo-Programm PYTHIA. Auf Grundlage der kinematischen Information aller beobachtbaren Teilchen untersuchen wir die Leistungsfähigkeit speziell entwickelter Variablen in der Trennung des Signals von Untergrundprozessen und die Chancen spezifischer Suchstrategien für Sleptonen in experimentell schwer zugänglichen supersymmetrischen Massenkonfigurationen

Singular order parameter interaction at nematic quantum critical point in two dimensional electron systems

We analyze the infrared behavior of effective N-point interactions between order parameter fluctuations for nematic and other quantum critical electron systems with a scalar order parameter in two dimensions. The interactions exhibit a singular momentum and energy dependence and thus cannot be represented by local vertices. They diverge for all N greater or equal 4 in a collinear static limit, where energy variables scale to zero faster than momenta, and momenta become increasingly collinear. The degree of divergence is not reduced by any cancellations and renders all N-point interactions marginal. A truncation of the order parameter action at quartic or any other finite order is therefore not justified. The same conclusion can be drawn for the effective action describing fermions coupled to a U(1) gauge field in two dimensions.Comment: 18 pages, 1 figur

Slepton pair production in the POWHEG BOX

We present an implementation for slepton pair production at hadron colliders in the POWHEG BOX, a framework for combining next-to-leading order QCD calculations with parton-shower Monte-Carlo programs. Our code provides a SUSY Les Houches Accord interface for setting the supersymmetric input parameters. Decays of the sleptons and parton-shower effects are simulated with PYTHIA. Focussing on a representative point in the supersymmetric parameter space we show results for kinematic distributions that can be observed experimentally. While next-to-leading order QCD corrections are sizable for all distributions, the parton shower affects the color-neutral particles only marginally. Pronounced parton-shower effects are found for jet distributions.Comment: 10 pages, 4 figure

Single-top production in the s-channel and the top-quark mass

We use a fixed-order expansion of resummed soft-gluon corrections to determine an approximate NNLO formula for the partonic cross section of single-top production in the $s$-channel. This formula is implemented in the program Hathor for the numerical evaluation of hadronic cross sections. With the resulting code, we perform a fit of the top-quark mass to Tevatron cross section data. Results for $m_t$ are given in the pole-mass scheme and in the $\overline{\mathrm{MS}}$ scheme

Slepton Pair Production in Association with a Jet: NLO-QCD Corrections and Parton-Shower Effects

We present a calculation of the next-to-leading order QCD corrections to slepton pair production in association with a jet at the LHC together with their implementation in the POWHEG BOX. For the simulation of parton-shower effects and the decays of the sleptons we employ the multi-purpose Monte-Carlo program PYTHIA. We discuss the impact of next-to-leading order QCD corrections on experimentally accessible distributions and illustrate how the parton shower can modify observables that are sensitive to QCD radiation effects. Having full control on the hard jet in the process, we provide precise predictions also for monojet analyses

Slepton pair production in association with a jet: NLO-QCD corrections and parton-shower effects

We present a calculation of the next-to-leading order QCD corrections to slepton pair production in association with a jet at the LHC together with their implementation in the POWHEG BOX. For the simulation of parton-shower effects and the decays of the sleptons we employ the multi-purpose Monte-Carlo program PYTHIA. We discuss the impact of next-to-leading order QCD corrections on experimentally accessible distributions and illustrate how the parton shower can modify observables that are sensitive to QCD radiation effects. Having full control on the hard jet in the process, we provide precise predictions also for monojet analyses