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This dissertation presents searches for direct pair production of a scalar partner of the top quark in events with only jets and \acrlong{met} in proton--proton collisions recorded during LHC Run 1 and Run 2 with the ATLAS detector. In the supersymmetry scenario, the partner is called top squark or stop. The stop ($\stop$) is assumed to decay via $\stop \to t \ninoone$, $\stop\to b\chinoonepm \to b W^{\left(\ast\right)} \ninoone$, or $\stop\ra bW\ninoone$, where $\ninoone$ ($\chinoonepm$) denotes the lightest neutralino (chargino). Exclusion limits are reported in terms of the stop and neutralino masses. The LHC Run 1 analysis uses an integrated luminosity of 20.1~{\ifb} at $\acrshort{sqrts}=8~\tev$ to exclude top squark masses in the range $270$--$645~\GeV$ for $\ninoone$ masses below $30~\GeV$, assuming a 100\% $\stop \to t \ninoone$ \gls{br}. For a \gls{br} of $50\%$ to either $\stop \to t \ninoone$ or $\stop\to b\chinoonepm$, and assuming $m_{\chinoonepm} = 2 m_{\ninoone}$, stop masses in the range $250$--$550~\GeV$ are excluded for $\ninoone$ masses below $60~\GeV$. The LHC Run 2 analysis uses an integrated luminosity of 13.3~{\ifb} at $\acrshort{sqrts}=13~\tev$. Assuming a 100\% $\stop \to t \ninoone$ \gls{br}, stop masses in the range $310$--$820~\GeV$ are excluded for $\ninoone$ masses below $160~\GeV$. For $\mstop\sim m_t+\mLSP$ scenario, the search excludes stop masses between $23$--$380~\GeV$. Additionally, scenarios where stops are produced indirectly through gluino decay but have very low $p_T$ signature due to a very small $\Delta (\mstop, \mLSP)$, have been considered. The result is interpreted as an upper limit for the cross section in terms of the gluino and stop masses. This excludes all models considered which include $m_{\gluino}$ up to 1600~\GeV\ with $\mLSP<560~\GeV$ at 95\% CL. Finally, the analysis strategy from the LHC Run 1 search is applied in the broader scope of supersymmetry called \gls{pmssm}. This dissertation presents a summary of the results that related to the stop search.

Two decay channels of the ω(782) meson, into π+π-π0 and π+π-, are studied. The dynamics of the three-pion channel is represented using a two-dimensional distribution, called a Dalitz plot. A high-statistics Dalitz plot distribution is needed to test theoretical predictions and increase understanding of the decay mechanism. The isospin-breaking two-pion decay gives insight into the ρ-ω mixing. The ω→π+π- decay has previously been studied in π+π- spectra in high statistics e+e- experiments and with lower statistics in hadroproduction experiments. The collected evidence indicates that the resulting interference pattern strongly depends on the production reaction. In 2011 an experiment to investigate ω hadronic decays in pd→3Heω reaction was performed with the WASA detector. Two studies based on the collected data are included in this thesis. In the first, the dominant decay channel ω→π+π-π0 is selected and two experimental Dalitz plot distributions are created. Each distribution corresponds to one of the two incident beam energies used in the experiment. A fit to the Dalitz plots is performed using a parametrisation including the expected P-wave shape. The result indicates an onset of the intermediate ρ in the two-pion channel, as predicted by theoretical models. The efficiency corrected Dalitz plot bin contents are reported to facilitate comparison to theoretical predictions by direct fits to the experimental data. In the second study, the ω→π+π- decay channel is selected. For events with a 3Heπ+π- final state, the 3He missing mass is constructed in search for the ρ-ω interference pattern in pd production. No significant deviations around the ω mass position was found. Dedicated studies using experimental data to estimate background contribution and to extract signal acceptance shows that the background is too large to observe the expected signal with the collected data sample. The last part of the thesis presents pre-studies for using data collected at the KLOE detector for an ω→π+π-π0 Dalitz plot analysis. Since the ω mesons are produced in the e+e-→ωπ0 reaction, the study focuses on the impact of the π0-π0 interference.

A study is presented on the production of vector boson (W and Z0) events in association with recoiling hadronic activity in the form of hadronic jets, using proton-proton collisions at the LHC. The dataset was taken by the ATLAS detector during the 2011 data-taking run, at a centre of mass energy p s = 7 TeV, and corresponds to an integrated luminosity of 4.6 fb 1. A measurement of the cross-section ratio of W+jets Z+jets events is de ned, reducing the large systematic uncertainties inherent in the experimental measurement of such events. Inclusive and di erential cross-sections are presented for W+jets Z+jets , as a function of a range of kinematic variables, and are compared to state-of- the-art theoretical predictions.

xix, 149 p. ; ill. (some col.) A print copy of this title is available through the UO Libraries. Search the library catalog for the location and call number. / We report on a study of the invariant mass spectrum of the hadronic system in à - [arrow right] à - à 0 à à à à à ½ à decays. This study was performed using data obtained with the BABAR detector operating at the PEP-II e + e - collider. We present fits to phenomenological models in which resonance parameters associated with the à (770), à '(1450) and à "(1700) mesons are determined. We also discuss the implications of our data with regard to estimates of the hadronic contribution to the muon anomalous magnetic moment. / Adviser: Eric Torrence

abstract: This work presents analysis and results for the NPDGamma experiment, measuring the spin-correlated photon directional asymmetry in the $\vec{n}p\rightarrow d\gamma$ radiative capture of polarized, cold neutrons on a parahydrogen target. The parity-violating (PV) component of this asymmetry $A_{\gamma,PV}$ is unambiguously related to the $\Delta I = 1$ component of the hadronic weak interaction due to pion exchange. Measurements in the second phase of NPDGamma were taken at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS) from late 2012 to early 2014, and then again in the first half of 2016 for an unprecedented level of statistics in order to obtain a measurement that is precise with respect to theoretical predictions of $A_{\gamma,PV}=O(10^{-8})$. Theoretical and experimental background, description of the experimental apparatus, analysis methods, and results for the high-statistics measurements are given. / Dissertation/Thesis / Doctoral Dissertation Physics 2017

Double hard parton-parton interactions are expected to occur frequently in proton-proton (p-p) collisions at the LHC. They can give rise to significant backgrounds to certain rare single scattering (SPS) signals, and are an interesting signal process in their own right. In this thesis, we discuss the theoretical description of the double parton scattering (DPS) cross section in the context of Quantum ChromoDynamics (QCD). After an overview of QCD and an introduction to DPS in Chapter 1, we describe in Chapter 2 a framework for calculating the p-p DPS cross section introduced by Snigirev et al., in which this cross section is expressed in terms of double PDFs D_p {ij}(x_1,x_2,Q_A 2,Q_B 2) (dPDFs). We show that the equal-scale dPDFs are subject to momentum and number sum rule constraints, and use these in the construction of an explicit set of leading order (LO) equal-scale dPDFs (the 'GS09' dPDFs). The leptonic same-sign WW DPS signal obtained using GS09 dPDFs is compared with that obtained using simple factorised forms, and the prospects of observing this signal taking into account SPS backgrounds are analysed. We discuss two ways in which the dPDF framework for describing p-p DPS is deficient in Chapter 3. We discuss interference and correlated parton effects in flavour, spin, colour, and parton type, which are ignored by the dPDF framework. We then study DPS-type graphs in which the parton pairs from both protons have arisen from a perturbative 1-&gt;2 branching, derive an expression for the part of such graphs associated with the particles arising from the 1-&gt;2 branchings being almost on-shell, and use this to demonstrate that the treatment of these graphs by the the dPDF framework is unsatisfactory. In Chapter 4, we study DPS-type graphs in which the parton pair from only one proton has arisen from a perturbative 1-&gt;2 branching. We discover that such graphs contribute to the LO p-p DPS cross section, and that crosstalk between partons in the 'nonperturbatively generated' pair is allowed provided that it occurs at a lower scale than that of the perturbative 1-&gt;2 branching in the other proton. The result of this analysis is combined with that of the previous chapter to propose a formula for the LO total DPS cross section, and our proposal is compared with those from other authors. We finish in Chapter 5 with some conclusions and suggestions for further work.

Ce travail de thèse s'inscrit dans le cadre de la physique hadronique et consiste en des études phénoménologiques et expérimentales dédiées à la structure interne des nucléons et reliées aux mesures des facteurs de forme des hadrons dans les régions temps et espace. Dans le cadre du futur complexe accélérateur d'antiprotons et d'ions (FAIR - Facility for Antiproton and Ion Research) à Darmstadt, Allemagne, un programme expérimental dont le but est la mesure des facteurs de forme électromagnétiques du proton dans la région temps est prévu auprès du détecteur de grande acceptance PANDA (anti-Proton Annihilation at Darmstadt) à partir des réactions d'annihilation pbar p -> e+ e- dans l'intervalle en énergie 2.25(1.5) <sqrt(s)(p L ) < 5.47(15) GeV (GeV/c), où sqrt(s)(p L ) est l'énergie totale dans le système centre de masse (l'impulsion du faisceau dans le référentiel du laboratoire). La difficulté réside dans l'extraction du signal d'intérêt dans le bruit de fond des voies hadroniques, principalement la production d'une paire de pions chargés. L'étude phénoménologique de la production d'une paire de mésons dans l'annihilation pbar p représente l'un des sujets de cette thèse. Le but de cette étude est double : d'une part, être capable de mieux évaluer le bruit de fond hadronique et d'autre part, accroître nos connaissances sur la structure interne des hadrons car une telle réaction contient des informations sur le contenu en quarks des nucléons. Un modèle effectif de mésons a été développé pour évaluer la section efficace d'annihilation pbar p en une paire de pions légers, dans le domaine en énergie d’intérêt. Un facteur de forme logarithmique a été introduit pour modéliser la nature composite des hadrons en interaction. Ce modèle s'applique aussi à la diffusion élastique pion proton, par symétrie de croisement, et à la production d'une paire de kaons chargés, suivant la symétrie SU(3). Le modèle a été ensuite étendu à différentes voies neutres telles pi0-pi0, eta-eta, pi0-eta. Les résultats obtenus sont présentés et comparés aux données existantes. Dans la région espace, l'effort expérimental entrepris à Jefferson Lab (Newport News, VA, USA) et dédié à la mesure précise du rapport des facteurs de forme électromagnétiques du proton dans la diffusion élastique doublement polarisée ep, sera poursuivi à plus haut quadri-moment transféré carré, au-dessus de 10 GeV2, et concernera aussi le neutron. Cette méthode nécessite une mesure précise de la polarisation du proton ou du neutron de recul. Pour concevoir et optimiser la polarimétrie dans la région du GeV, une détermination de l'efficacité et des pouvoirs d'analyse, c'est-à-dire de la figure de mérite d'un polarimètre, est indispensable préalablement aux expériences à JLab. Dans ce contexte, j'ai contribué à l'expérience ALPOM2 (JINR Dubna, Russie), la seule expérience actuellement capable de mesurer les pouvoirs d'analyse protons et neutrons pour les mesures à JLab avec plusieurs types de cibles. Expérimentalement, un faisceau polarisé de protons ou de neutrons de 3.0, 3.75 et 4.2 GeV/c est obtenu par cassure du faisceau de deutons polarisés du Nuclotron et les fragments chargés issus des collisions avec les cibles de C, CH2, CH et Cu sont mesurés. Pour les neutrons, dans l'intervalle en impulsion de 1 à 6 GeV/c, deux processus ont été considérés pour déterminer les pouvoirs d'analyse : np -> np, et réaction avec échange de charge np -> pn. A partir de la comparaison des figures de mérite associées à chacun de ces deux processus, calculés par un modèle, la réaction avec échange de charge apparaît comme plus efficace pour la polarimétrie à haute énergie. Les pouvoirs d'analyse du neutron pour la réaction d'échange de charge sur des cibles CH et Cu ont été mesurés pour la première fois jusqu'à 4.2 GeV/c. Pour le proton, des données plus précises de pouvoir d'analyse ont été obtenues. Les résultats expérimentaux de l'analyse préliminaire sont présentés. / This thesis work, set in the framework of hadron physics, reports on a phenomenological and an experimental studies dedicated to nucleon internal structure, both related to hadron electromagnetic form factor measurements in the time-like and in the space-like regions.At the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, an experimental program aiming to determine the proton electromagnetic form factors in the time-like region is planned with the PANDA (anti-Proton Annihilation at Darmstadt) large acceptance detector through the annihilation reaction pbar p -> e+ e- in the energy range 2.25(1.5) <sqrt(s)(p L ) < 5.47(15) GeV (GeV/c), where sqrt(s)(p L ) is the total energy in the center of mass system (the beam momentum in laboratory frame). In such reactions, the difficulty is to extract the signal of interest from the huge background coming from hadronic channels, mainly pion pair production. Phenomenological studies of meson pair production in pbar p annihilation is one of the subjects of this thesis. The goal is two-fold : to better evaluate the hadronic background and to improve our knowledge on the hadron internal structure as such reaction contains by itself useful information on the hadron quark content. An effective meson model has been developed to evaluate the cross section of pbar p annihilation into light meson pairs, in the energy domain relevant to the PANDA experiment. A logarithmic form factor is introduced to account for the composite nature of the interacting hadrons. The model was also applied to pi p elastic scattering, using crossing symmetry, and to charged kaon pair production, on the basis of SU(3) symmetry. The model has then been extended to different neutral channels pi0-pi0, eta-eta, eta-pi0 relying on SU(3) symmetry. In the range 3.362(5) <sqrt(s)(p L ) < 4.559(10.1) GeV (GeV/c), the results obtained are presented and compared to existing data.In the space-like region, the experimental effort started at Jefferson Lab (Newport News, VA, USA) and dedicated to precise measurements of the proton electromagnetic form factor ratio based on the recoil polarization method in elastic ep scattering, will be pursued up to higher four-momentum transfer squared, above 10 GeV2, and will be also applied to neutron. This method requires an accurate measurement of the polarization of the recoil particle, the proton or the neutron. In order to design and optimize the polarimetry in the GeV region, the determination of the efficiency and the analyzing powers, that combine into the figure of merit of a polarimeter, is mandatory prior to perform the experiments at JLab. In this context I contributed to the ALPOM2 experiment (JINR Dubna, Russia), the only experiment right now able to measure proton and neutron analyzing powers in the momentum range of interest for Jefferson Lab measurements and allowing considering different types of target. Experimentally, in the framework of ALPOM2, from the Nuclotron polarized deuteron beam, polarized proton and neutron beams at 3.0, 3.75 and 4.2 GeV/c were obtained by deuteron break-up and the charged fragments from the collisions with C, CH2, CH and Cu targets were measured. For neutrons, in the range from 1 to 6 GeV/c, two processes have been considered to determine the analyzing powers: np -> np and the charge exchange reaction np -> pn. From the comparison of the figures of merit associated to each of these two processes, the charge exchange reaction appears to be more efficient for polarimetry at high energy. Neutron analyzing powers for the charge exchange reaction on CH, and Cu targets have been measured up to 4.2 GeV/c for the first time. For the proton, more precise analyzing power data have been obtained. Experimental results of preliminary analysis are presented.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23597号 / 理博第4759号 / 新制||理||1682(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)長野 邦浩, 教授 中家 剛, 准教授 吉岡 興一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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