This thesis presents a search for Supersymmetry in final states containing two same-flavor opposite-sign leptons, jets and large missing transverse momentum. The search makes use of 36.1 fb−1 of proton-proton collision data collected at a center-of-mass energy of √s = 13 TeV by the ATLAS detector at the Large Hadron Collider. Two signal scenarios, which both involve the pair-production of squarks or gluinos decaying into final states with two leptons and the lightest supersymmetric particle, are targeted by the analysis. The first scenario considers decay chains with a leptonically decaying Z boson and is characterized by a peak in the dilepton invariant mass distribution. In the second scenario, decays through intermediate sleptons or an off-shell Z boson are considered. Such processes lead to a kinematic endpoint in the dilepton invariant mass distribution. The main Standard Model backgrounds include the pair-production of top quarks and direct production of Z bosons. These backgrounds are estimated with two data-driven methods. The observed data is found to be consistent with the Standard Model expectation and the results are interpreted in simplified Supersymmetry models for gluino and squark pair-production. Sensitivity is provided for gluino and squark masses up to 1.85 TeV and 1.3 TeV respectively. / I denna avhandling presenteras en analys som letar efter supersymmetriska partiklar producerade i proton-proton-kollisioner vid en kollisionsenergi på √s = 13 TeV. Analysen använder sig av data insamlad under 2015 och 2016 av ATLAS-experimentet vid CERNs Large Hadron Collider. Den totala analyserade datamängden motsvarar 36,1 fb−1. Kollisioner som resulterar i par av elektroner eller myoner med motsatt laddning, jets och en stor obalans i rörelsemängd i det transversella planet väljs ut för analys. Målet är att finna tecken på en produktion av skvarkar eller gluiner som sönderfaller till två leptoner och en oladdad supersymmetrisk partikel som lämnar detektorn utan att lämna någon signal. Inom supersymmetriska modeller kan sådana slutliga tillstånd uppkomma genom sönderfallskedjor med Z-bosoner som sönderfaller leptoniskt, eller genom sönderfallskedjor med sleptoner. Flera processer som förutspås av Standardmodellen kan efterlikna den eftersökta signalen och utgör bakgrunder i analysen. De viktigaste bakgrunderna består av Z-bosoner och par av toppkvarkar som produceras direkt i proton-proton-kollisionerna. Dessa bakgrunder uppskattas genom att använda data, medan andra mindre bakgrunder uppskattas genom att använda simuleringar. Ingen signifikant signal utöver den uppskattade backgrunden uppmäts i analysen. Istället tolkas resultaten med hjälp av simuleringar av förenklade supersymmetriska modeller. På så sätt kan exkluderingsgränser med 95% konfidensnivå beräknas för gluino- och skvark-massorna. Massor över 1,85 TeV utesluts för gluiner och massor över 1,3 TeV utesluts för skvarkar. / <p>QC 20180109</p>

Gauge theories is one of the most pervasive and important subject of modern theoretical physics, and there are still many things about them we do not understand. In particular dealing with strongly coupled theories where normal perturbative techniques do not apply is a fundamental open problem. In this thesis, we study a particular class of toy-models that have supersymmetry, which makes them much easier to deal with. We employ the mathematical technique of localization, which for supersymmetric theories lets us evaluate certain path integrals exactly and for any value of the coupling. This is used to study the 5d N=1 theories placed on toric Sasaki-Einstein manifolds and compute their partition functions, finding that they factorize into a product of contributions from each closed Reeb orbit of the manifold. This computation leads us to define two new hierarchies of special functions associated to these manifolds, and we study their properties. Finally, we use the 5d N=1 theories to construct new 4d N=2 theories on a large class of curved backgrounds. These theories have some interesting features, such as supporting both instantons and anti-instantons, and having a position-dependent complexified coupling constant.

<p>Frisch grid ionization chambers are commonly used experimental tools for charged particle spectroscopy. In the ideal Frisch grid chamber the anode pulse height is independent of where inside the sensitive volume the charge has been created. This ideal cannot be realized because of imperfect shielding of the anode by the grid. The effect of the imperfect shielding is generally referred to as grid inefficiency. For accurate energy determination the anode pulse height needs to be corrected for this.</p><p>At present two opposing explanation for grid inefficiency exist. The first explanation suggests that there is a reduction of the anode pulse height. This is said to arise from positive ions inducing charge on the anode as the electrons are collected. The second explanation suggests that there is a too large anode signal. The addition to the anode signal is said to arise from the drift of electrons.</p><p>In this thesis the concept of grid inefficiency is investigated by means of wave form digitization. The use of digital signal processing makes it possible to maintain information on the drift of electrons. This information is lost in charged particle spectroscopy experiments using electronic signal processing networks.</p><p>A series of experiments is described in this thesis. The first experiment was performed to find good measuring conditions for the following experiments. For this purpose the drift velocity of electrons was measured in two chamber filling gases, P-10 and CF4. The measured drift velocities are presented for the two gases. Finally, P-10 was chosen as filling gas for the following experiments.</p><p>In the second experiment the grid inefficiency was measured for two different types of shielding electrodes. The method of determining the grid inefficiency is based on the analysis of the shape of digitized charge signals. The measured values are shown to be in good agreement with calculated values.</p><p>In the final experiment the effects of grid inefficiency on alpha particle spectroscopy is investigated. It is shown how the correction for grid inefficiency by the two existing models yield equivalent results for energy determination. An attempt to separate the two models is also presented indicating that there is in fact a reduction of the anode pulse height because of grid inefficiency. The thesis is concluded with a theoretical discussion of the anode pulse shape. There grid inefficiency is explained by the drift of electrons. It is shown in this section how explaining grid inefficiency by the drift of electrons should yield the same result as explaining it by the effect of positive ions.</p>

The Gesellschaft für Schwerionenforschung (GSI) facility in Darmstadt, Germany, will be upgraded to accommodate a new generation of physics experiments. The future accelerator facility will be called FAIR and one of the experimentsat the site will be PANDA, which aims at performing hadron physics investigations by colliding anti-protons with protons. The licentiate thesis consistsof three sections related to PANDA. The first contains energy resolutionstudies of PbWO4 crystals, the second light yield uniformity studies of PbWO4 crystals and the third reconstruction of the lambda-bar-polarisation in the PANDA experiment. Two measurements of the energy resolution were performed at MAX-Lab in Lund, Sweden, with an array of 3x3 PbWO4 crystals using a tagged photon beam with energies between 19 and 56 MeV. For the April measurement, the crystals were cooled down to -15 degrees C and for the September measurement down to -25 degrees C. The measured relative energy resolution, <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csigma" />/E, is decreasing from approximately 12% at 20 MeV to 7% at 55 MeV. In the standard energy resolution expression <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csigma" />/E = a/<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csqrt%5B%5D%7BE%7D" /> <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Coplus" /> b/E <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Coplus" /> c, the three parameters a, b and c seem to be strongly correlated and thus difficult to determine independently over this relative small energy range. The value of a was therefore fixed to that one would expect from Poisson statistics of the light collection yield (50 phe/MeV) and the results from fits were <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csigma" />/E=0.45%/<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csqrt%5B%5D%7BE_%7BGeV%7D%7D" /> <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Coplus" />0.18%/EGeV <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Coplus" />8.63% and <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csigma" />/E = 0.45%/<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csqrt%5B%5D%7BE_%7BGeV%7D%7D" /><img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Coplus" />0.21%/EGeV <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Coplus" />6.12% for the April and September measurements, respectively. The data from the September measurement was also combined with previous data from MAMI for higher energies, ranging from approximately 64 to 715 MeV. The global fit over the whole range of energies gave an energy resolution expression of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csigma" />/E = 1.6%/<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csqrt%5B%5D%7BE_%7BGeV%7D%7D" /> <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Coplus" />0.095%/EGeV <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Coplus" />2.1%. Light yield uniformity studies of five PbWO4 crystals, three tapered and two non-tapered ones, have also been performed. The tapered crystals delivered a light output which increased with increasing distance from the Photo Multiplier Tube (PM tube). Black tape was put on different sides of one tapered crystals, far from the PM tube to try to get a more constant uniformity prole. It was seen that the light output profile depends on the position of the tape. Generally, the steep increase in light output at large distances from the PM tube could be damped. The third part of the thesis concerns the reconstruction of the lambdabar polarisation in the reaction <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?pbar+p%20%5Crightarrow%20lambdabar%20+%20lambda" />. Events were generated using a modied generator from the PS185 experiment at LEAR. With a 100% polarisation perpendicular to the scattering plane, a polarisation of (99±1.8)% was reconstructed. Slight non-zero polarisations along the axis determined by the outgoing hyperon as well as the axis in the scattering plane, were also reconstructed. These were (4.1±2.1)% and (2.6±2.0)% respectively. From this investigation it was shown that the detector efficiency was not homogeneous and that slow pions are difficult to reconstruct.

No description available.

Frisch grid ionization chambers are commonly used experimental tools for charged particle spectroscopy. In the ideal Frisch grid chamber the anode pulse height is independent of where inside the sensitive volume the charge has been created. This ideal cannot be realized because of imperfect shielding of the anode by the grid. The effect of the imperfect shielding is generally referred to as grid inefficiency. For accurate energy determination the anode pulse height needs to be corrected for this. At present two opposing explanation for grid inefficiency exist. The first explanation suggests that there is a reduction of the anode pulse height. This is said to arise from positive ions inducing charge on the anode as the electrons are collected. The second explanation suggests that there is a too large anode signal. The addition to the anode signal is said to arise from the drift of electrons. In this thesis the concept of grid inefficiency is investigated by means of wave form digitization. The use of digital signal processing makes it possible to maintain information on the drift of electrons. This information is lost in charged particle spectroscopy experiments using electronic signal processing networks. A series of experiments is described in this thesis. The first experiment was performed to find good measuring conditions for the following experiments. For this purpose the drift velocity of electrons was measured in two chamber filling gases, P-10 and CF4. The measured drift velocities are presented for the two gases. Finally, P-10 was chosen as filling gas for the following experiments. In the second experiment the grid inefficiency was measured for two different types of shielding electrodes. The method of determining the grid inefficiency is based on the analysis of the shape of digitized charge signals. The measured values are shown to be in good agreement with calculated values. In the final experiment the effects of grid inefficiency on alpha particle spectroscopy is investigated. It is shown how the correction for grid inefficiency by the two existing models yield equivalent results for energy determination. An attempt to separate the two models is also presented indicating that there is in fact a reduction of the anode pulse height because of grid inefficiency. The thesis is concluded with a theoretical discussion of the anode pulse shape. There grid inefficiency is explained by the drift of electrons. It is shown in this section how explaining grid inefficiency by the drift of electrons should yield the same result as explaining it by the effect of positive ions.

In this thesis a characterization of air showers induced by magnetic monopoles is presented. Monopoles are predicted to exist and be accelerated to relativistic velocities. High energy monopoles traversing earth’s atmosphere continuously deposit energy, inducing an air shower. These air showers have been described based on simulations run in CORSIKA. It was found that monopole air showers are continuous; they plateau after the shower maximum, and have a large electromagnetic component. As such,they can easily be distinguished from normal cosmic rays and most other air shower sources. Very high energy photons and muons could induce similar showers but do not produce identical signals in track-following detectors such as IceCube.

In this review, several tools used in the study of super-Yang-Mills scattering amplitudes are discussed, namely spinor-helicity and (super)twistor variables. These variables are then implemented in string theories in 4D, and a suitable generalization to 10D using pure spinors is discussed. Dimensional reduction of this model to 4D is then performed, and some comparisons to other 4D models are drawn.

In this project we study the use of neural networks as a tool for particle track pattern recognition with the possibility of its implementation in the Trigger system at the ATLAS experiment [1]. By using a method named Hough transform we created a Convolutional Neural Network (CNN) that is able to train on the transformed images of muons merged with minimum bias. We give an overview of how the CNN works and compare the results from the CNN with the old cut based method. We believe to have managed to find an alternative to the previously used algorithm, that is faster and more efficient.

Uncertainties in radiative effects of the quarks in -background in the form of final state radiation (FSR) are significant when it comes to reducing all forms of systematics that can arise from measuring the jets energy. Analysis on FSR is in general conducted on different simulated samples where one has included the radiative effect using algorithms such as PYTHIA[29]. The hypothesis is that through the re-weighting of the -background nominal sample one could add a better representation of the FSR effect. Finding a simple way to include a better description of FSR would not only save time in the simulation process but it would also be a way to reduce the systematic errors originating from limited MC statistics. Due to statistical effects coming from the simulations one cannot use the basic approach to define the effect of FSR as simply the difference between nominal and FSR. Two methods are tested to estimate the FSR effects; the first method uses a set of efficiency factors to represent the signal regions, the second method is to add a weight to the events of the nominal sample. The first method show positive results, especially in SR2, compared to a basic analysis, with an uncertainty of the FSR effect of: SR1:±29% SR2: ±51% SR3: ±37%. While a basic analysis gave an uncertainty of ±42%, ±122% and 36%. The second method shows positive signs where the re-weighted sample moves closer to the behaviour of the FSR sample. However, both methods are based on insufficient amount of statistics to draw any absolute conclusions.