The NPDGamma Experiment is used to study the n + p to d + g reaction for the purpose of examining the hadronic weak interaction. The nucleon-nucleon interaction is overwhelmingly mediated by the strong force, however, the weak part can be extracted by a study of its parity violating manifestations. When neutrons are incident on protons, deuterons and 2.2 MeV gamma rays are produced. If the incoming neutrons are polarized, the parity violating weak interaction gives rise to a measured spatial asymmetry, Ag, in the outgoing gamma rays, as sn · kg is parity odd. At low energies, the weak nucleon-nucleon interaction can be modeled as meson exchange and characterized with six parameters. NPDGamma is sensitive to one of these parameters, hp. Previous measurements that extrapolate hp from more complicated interactions disagree, and disagree with the theoretical reasonable range. Additionally, a previous iteration of the NPDGamma Experiment performed at Los Alamos National Lab was statistics limited in its measurement of Ag. For this reason, a new measurement was performed at the high neutron flux Spallation Neutron Source at Oak Ridge National Lab. In the experiment, a high flux of cold neutrons was polarized to ~ 95% by a supermirror polarizer, the spins flipped in a defined sequence by a radio-frequency spin rotator, and then the neutrons captured on a 16 L liquid para-hydrogen target, which emits gamma-rays asymmetrically upon capture. The gamma-rays are detected in a 3pi array of 48 CsI crystal detectors. This thesis discusses the NPDGamma Experiment in detail, and includes an analysis of subset of the NPDGamma data that has unique timing and data acquisition properties that preclude it being analyzed with the combined data set. Ag was extracted with a result of (6.254 ± 37.694) × 10-9

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

abstract: This thesis deals with the first measurements done with a cold neutron beam at the Spallation Neutron Source at Oak Ridge National Laboratory. The experimental technique consisted of capturing polarized cold neutrons by nuclei to measure parity-violation in the angular distribution of the gamma rays following neutron capture. The measurements presented here for the nuclei Chlorine ( 35Cl) and Aluminum ( 27Al ) are part of a program with the ultimate goal of measuring the asymmetry in the angular distribution of gamma rays emitted in the capture of neutrons on protons, with a precision better than 10-8, in order to extract the weak hadronic coupling constant due to pion exchange interaction with isospin change equal with one ( hπ 1). Based on theoretical calculations asymmetry in the angular distribution of the gamma rays from neutron capture on protons has an estimated size of 5·10-8. This implies that the Al parity violation asymmetry and its uncertainty have to be known with a precision smaller than 4·10-8. The proton target is liquid Hydrogen (H2) contained in an Aluminum vessel. Results are presented for parity violation and parity-conserving asymmetries in Chlorine and Aluminum. The systematic and statistical uncertainties in the calculation of the parity-violating and parity-conserving asymmetries are discussed. / Dissertation/Thesis / Ph.D. Physics 2012

Weak nucleon nucleon couplings are largely unknown because of the involved theoretical and experimental challenges. Theoretically the topic is difficult due to the non-perturbative nature of the strong interaction, which makes calculations of the couplings challenging. Experimentally, the topic is difficult given that 1) the observables are determined by ratios between strong couplings and weak couplings which differ in size by seven orders of magnitude, and 2) theoretically clean and predictable measurements are almost always restricted to simple systems that do not allow for effects that enhance the size of the asymmetry. However parity violation (PV) can be used to separate out the weak part and thus studies of PV in hadronic systems could offer a unique probe of nucleon structure. The n-3He experiment at the Spallation Neutron Source was performed to measure the parity violating asymmetry of the recoil proton momentum kp with respect to the neutron spin in the reaction n + 3He ---> p + T + 764 keV. This asymmetry is sensitive to the isospin-conserving and isospin-changing (∆I = 0, 1, 2) parts of the Hadronic Weak Interaction (HWI), and is expected to be small (~10-7). The goal of this experiment was to determine this PV asymmetry with a statistical sensitivity of 2x10-8. We also measured the parity even nuclear asymmetry proportional to kp · σn x kn for the first time for verification of nuclear theory and for confirmation of the sensitivity of our experiment to the parity violating asymmetry.

Dans cette thèse, on étudie le phénomène de localisation d'Anderson des opérateurs de Schrödinger à N particules qui englobe aussi bien la localisation exponentielle des fonctions propres que la localisation dynamique. Dans un premier temps, on considère le modèle d'Anderson discret multi- particulaire avec un potentiel aléatoire à valeurs indépendantes et identiquement distribuées i.i.d. dont la distribution commune est au moins log-Höldérienne et une interaction de courte portée. On établit pour ce modèle la localisation d'Anderson pour les énergies susamment proches du bas du spectre après avoir montré qu'il est non-aléatoire. D'autre part, on montre que la localisation complète des systèmes mono- particulaires s'étend aux systèmes multi-particulaires ayant une interaction globale susamment faible et pour un désordre arbitraire. Pour ce résultat, l'existence d'une densité bornée de la distribution commune des variables aléatoires i.i.d. est nécessaire et on le montre pour des interactions ayant une forme très générale mais bornées. Les résultats sont démontrés à l'aide de l'adaptation aux systèmes multi- particulaires de l'analyse multi-échelle à énergie variable qui permet de traiter des distributions singulières contrairement à la méthode des moments fractionnaires. Les estimées de Wegner intervenant notamment dans l'analyse multi-échelle sont établies pour des cubes vériant une propriété de séparabilité en utilisant le Lemme de Stollmann. On démontre également l'estimée de Combes-Thomas qui joue un rôle important dans l'analyse des énergies extrêmes. / In this thesis, we study for the N-particles Schrodinger operators the Anderson localization phenomenon which consists of both exponential localization of eigenfunctions and dynamical localization. We rst consider the discrete multi-particle Anderson model with a short range interaction and a random potential whose values are independent and identically distributed i.i.d. with a log-Hölder continuous common probability distribution function. For such model, we show that the bottom of its spectrum is non-random and prove the Anderson localization for energies suciently close to the spectral edge. On the other hand, we establish that the complete localization from singleparticle systems extends to multi-particle systems with suciently weak interaction at arbitrary disorder and for absolute continuous probability distribution function of the i.i.d random variables. The results are proved by an adaptation to multi-particle systems of the vari- able energy multi-scale analysis which allows singular distributions instead of the fractional moments method. Wegner bounds, useful for the multi-scale analysis are proved for separable cubes using the Stollmann's Lemma. We also prove the Combes-Thomas estimate which plays an important role in the analysis of extreme energies.

The study of the muon decay process μ+ → e+νeν ̄μ is a powerful constraint on the behaviour of the weak interaction, without contamination of the other, stronger, fundamental interactions. The spectrum measured from the momentum and angles of the decay positrons is parametrized using a set of four decay parameters. The purpose of the TWIST experiment is to measure these decay parameters to an unprecedented precision; an order of magnitude improvement in the uncertainties over measurements completed before the TWIST experiment. Measurements of the muon decay parameters constrain the values of a series of 19 weak coupling constants. In the standard model, V-A weak interaction, 18 of these constants are 0, while the remaining constant describes interactions between left handed particles, gV_LL= 1.The decay parameter ρ quantifies the behaviour of the spectrum with respect to momentum. According to the standard model the value of this parameter is 3/4. TWIST measured a value of ρ = 0.74991±0.00009(stat)±0.00028(sys). The measurement is limited by its systematic uncertainty, so a large focus of the experiment was on the determination and control of these uncertainties. The systematic uncertainties are derived from uncertainties in the detector construction and uncertainties in the biases generated by differences between the data and a matching Monte Carlo. Muon decay also limits the possibility of family symmetry breaking interactions. TWIST can be used to search for the possibility of muons decaying into a positron and a single unidentified neutral particle μ+ → e+X0 that does not otherwise interact with normal matter. The large momentum and angle acceptance of the TWIST spectrometer allows for searches of two body decays for masses of the X0 boson mX0 ∈ [0,80] MeV/c, with a variety of behaviours with respect to the angle of the positron track. Upper limits on massive and mass-less X0 decays are set with a 90% confidence level separately at parts per million for massive decays and parts in 10000 for mass-less decays.

Cette thèse présente une mesure de la section efficace de production du quark-top célibataire en voie t avec 1,04~fb^{-1} de données recueillies par le détecteur ATLAS au LHC à partir de collisions proton-proton d'énergie centre de masse sqrt(s) = 7TeV. Les événements sélectionnés contiennent un lepton, de l'énergie transverse manquante, et deux ou trois jets, l'un d'eux étant étiqueté comme étant issu d'un quark-b. Le modèle pour le bruit de fond se compose des processus multijets, W+jets et production de paires de quarks top ainsi que de contributions moindres venant d'événements Z+jets et diboson. En utilisant une méthode de coupures et de comptage basée sur la distribution d'un discriminant multivarié construit avec des arbres de décision stimulés, la section efficace de production de quark-top célibataire en voie t a été mesurée. La valeur sigma_ {t} = 97,3^{30,7}_{-30,2}~pb a été obtenue. Ce résultat est en bon accord avec la prédiction du Modèle Standard. En supposant que les éléments de la matrice CKM reliee au quark-top obéissent à la relation |Vtb|>>|Vts|, |V_td|, la force du couplage W-t-b est extraite de la section mesurée, |Vtb| = 1,23^{+0,20}_{-0,19}. Si on suppose que |Vtb|<1, une limite inférieure |Vtb|>0.61 est obtenue avec un niveau de confiance de 95%. / This thesis presents a measurement of the cross section of t-channel single top-quark production using 1.04~fb^{-1} data collected by the ATLAS detector at the LHC with proton-proton collision at center-of-mass sqrt(s)=7TeV. Selected events contain one lepton, missing transverse energy, and two or three jets, one of them b-tagged. The background model consists of multijets, W+jets and top-quark pair events, with smaller contributions from Z+jets and diboson events. By using a cut and count method based on the distribution of a multivariate discriminant constructed with the boosted decision trees, the cross section of t-channel single top-quark production is measured: sigma_{t}= 97.3^{+30.7}_{-30.2}~pb, which is in good agreement with the prediction of the Standard Model. Assuming that the top-quark-related CKM matrix elements obey the relation |Vtb|>>|Vts|, |V_td|, the coupling strength at the W-t-b vertex is extracted from the measured cross section, |Vtb| = 1,23^{+0,20}_{-0,19}. If it is assumed that |Vtb|<1, a lower limit of |Vtb|>0.61 is obtained at the 95% confidence level.

Cette thèse présente une étude de la production de boson de Higgs dans les collisions proton-proton à sqrt(s) = 13 TeV enregistrées avec le détecteur CMS au Grand collisionneur de hadrons (LHC) du CERN, exploitant la voie de désintégration en une paire de bosons Z qui se désintègrent à leur tour en paires d’électrons ou de muons (H->ZZ->4l, l = e,mu).Ce travail s’inscrit dans le contexte du début du Run II du LHC, une nouvelle période de prise de données qui a commencé en 2015 après une interruption de deux ans. Ce redémarrage est marqué par une augmentation de l’énergie dans le centre de masse de 8 TeV à 13 TeV et un resserrement de l’espacement entre paquets de protons de 50 ns à 25 ns. Ces nouveaux paramètres augmentent à la fois la luminosité et placent des contraintes inédites sur le déclenchement, la reconstruction et l’analyse des données de collisions pp. Un effort important est donc consacré à l’amélioration et la réoptimisation du système de déclenchement de CMS pour le Run II, en mettant l’accent sur la reconstruction et la sélection des électrons et sur la préparation de chemins de déclenchement multi-leptons préservant une efficacité maximale pour le canal H->ZZ->4l.Dans un second temps, les algorithmes de sélection hors-ligne des électrons et des muons sont optimisés et leurs efficacités sont mesurées dans les données, tandis que la logique de sélection des candidats à quatre leptons est améliorée. Afin d’extraire des modes de production rares du boson de Higgs tels que la fusion de bosons vecteurs, la production par « Higgsstrahlung » VH et la production associée ttH, une nouvelle répartition des événements sélectionnés en catégories exclusives est introduite, fondée sur des discriminants utilisant le calcul d’éléments de matrice et l’étiquetage de saveur des jets.Les résultats de l’analyse des premières données à 13 TeV sont présentés pour des lots de données enregistrés en 2015 et au début de 2016, qui correspondent à des luminosités intégrées respectives de 2.8 fb-1 and 12.9 fb-1. Le boson de Higgs est redécouvert de façon indépendante à la nouvelle énergie. L’intensité du signal relative à la prédiction du modèle standard, la masse et la largeur de désintégration du boson sont mesurées, ainsi qu’un jeu de paramètres contrôlant les contributions des principaux modes de production attendus. Tous les résultats sont en bon accord avec les prévisions du modèle standard pour un boson de Higgs à 125 GeV, aux incertitudes de mesure près, ces dernières étant dominées par la composante statistique avec l’échantillon de données actuel. Enfin, une autre résonance se désintégrant en quatre leptons est recherchée à haute masse, et aucun excès significatif n’est observé. / This thesis reports a study of Higgs boson production in proton-proton collisions at sqrt(s) = 13 TeV recorded with the CMS detector at the CERN Large Hadron Collider (LHC), exploiting the decay channel into a pair of Z bosons that in turn decay into pairs of electrons or muons (H->ZZ->4l, l = e,mu).This work is carried out in the context of the beginning of Run II of the LHC, a new data-taking period that started in 2015, following a two-year-long shutdown. This restart is marked by an increase of the centre-of-mass energy from 8 TeV to 13 TeV, and a narrowing of the spacing of proton bunches from 50 ns to 25 ns. These new parameters both increase the luminosity and set new constraints on the triggering, reconstruction and analysis of pp collision events. Therefore, considerable effort is devoted to the improvement and reoptimization of the CMS trigger system for Run II, focusing on the reconstruction and selection of electrons and on the preparation of multilepton trigger paths that preserve a maximal efficiency for the H->ZZ->4l channel.Secondly, the offline algorithms for electron and muon selection are optimized and their efficiencies are measured in data, while the selection logic of four-lepton candidates is improved. In order to extract rare production modes of the Higgs boson such as vector boson fusion, VH associated production and ttH associated production, a new classification of selected events into exclusive categories is introduced, using discriminants based on matrix-element calculations and jet flavour tagging.Results of the analysis of first 13 TeV data are presented for two data sets recorded in 2015 and early 2016, corresponding to integrated luminosities of 2.8 fb-1 and 12.9 fb-1, respectively. A standalone rediscovery of the Higgs boson in the four-lepton channel is achieved at the new energy. The signal strength relative to the standard model prediction, the mass and decay width of the boson, and a set of parameters describing the contributions of its main predicted production modes are measured. All results are in good agreement with standard model expectations for a 125 GeV Higgs boson within the incertainties, which are dominated by their statistical component with the current data set. Finally, a search for an additional high-mass resonance decaying to four leptons is performed, and no significant excess is observed.

High precision measurements of a weak interaction decay were conducted to search for possible variation of the decay rate parameter caused by an antineutrino flux. The experiment searched for variation of the ⁵⁴Mn electron capture decay rate parameter to a level of precision of 1 part in ∼10⁵ by comparing the difference between the decay rate in the presence of an antineutrino flux ∼3×10¹² cm^-2sec^-1 and no flux measurements. The experiment is located 6.5 meters from the reactor core of the High Flux Isotope Reactor (HFIR) in Oak Ridge National Laboratory. A measurement to this level of precision requires a detailed understanding of both systematic and statistical errors. Otherwise, systematic errors in the measurement may mimic fundamental interactions. <div><br></div><div>The gamma spectrum has been collected from the electron capture decay of ⁵⁴Mn. What differs in this experiment compared to previous experiments are, (1) a strong, uniform, highly controlled, and repeatable source of antineutrino flux, using a reactor, nearly 50 times higher than the solar neutrino flux on the Earth, (2) the variation of the antineutrino flux from HFIR is 600 times higher than the variation in the solar neutrino flux on the Earth, (3) the extensive use of neutron and gamma-ray shielding around the detectors, (4) a controlled environment for the detector including a fixed temperature, a nitrogen atmosphere, and stable power supplies, (5) the use of precision High Purity Germanium (HPGe) detectors and finally, (6) accurate time stamping of all experimental runs. By using accurate detector energy calibrations, electronic dead time corrections, background corrections, and pile-up corrections, the measured variation in the ⁵⁴Mn decay rate parameter is found to be δλ/λ=(0.034±1.38)×10^-5. This measurement in the presence of the HFIR flux is equivalent to a cross-section of σ=(0.097±1.24)×10^-25cm². These results are consistent with no measurable decay rate parameter variation due to an antineutrino flux, yielding a 68% confidence level upper limit sensitivity in δλ/λ <= 1.43×10^-5 or σ<=1.34×10^-25cm² in cross-section. The cross-section upper limit obtained in this null or no observable effect experiment is ∼10⁴ times more sensitive than past experiments reporting positive results in ⁵⁴Mn.</div>

Presented is a search for the rare hadronic B meson decay B0 -&amp;gt; eta phi. It is based on 86 x 10^6 BB pairs recorded by the BABAR experiment at the Stanford Linear Accelerator Center between 1999 and 2002. phi mesons are reconstructed in the channel phi -&amp;gt; K+ K-. eta mesons are reconstructed in the channels eta -&amp;gt; gamma gamma and eta -&amp;gt; pi+ pi- pi0. Signal events are identified by a candidate counting and a maximum-likelihood method. To ensure an unbiased measurement, the number of signal events is blinded throughout the analysis. Although no significant signal is found by either method, the maximum-likelihood method obtains a smaller statistical uncertainty. In this method, the branching fraction of the decay B0 -&amp;gt; eta phi is determined by the upper limit BR (B0 -&amp;gt; eta phi) &amp;lt; 3.28 x 10^-6 (90%). This value includes a systematic uncertainty of 6.2%. The cited upper limit is consistent with recent theoretical predictions. Therefore, this search gives no indication for particle interactions that are not described by the Standard Model of particle physics. / Vorgestellt wird eine Suche nach dem seltenen hadronischen B-Meson-Zerfall B0 -&amp;gt; eta phi. Sie basiert auf 86 x 10^6 BB-Paaren, die zwischen 1999 und 2002 vom BABAR-Experiment am Stanford Linear Accelerator Center aufgezeichnet wurden. phi-Mesonen werden im Kanal phi -&amp;gt; K+ K- rekonstruiert. eta-Mesonen werden in den Kanälen eta -&amp;gt; gamma gamma und eta -&amp;gt; pi+ pi- pi0 rekonstruiert. Zur Identifikation von Signalereignissen wird eine Abzählmethode und eine Maximum-Likelihood-Methode verwendet. Um eine unvoreingenommene Messung zu gewährleisten, bleibt die Anzahl der Signalereignisse während der gesamten Analyse blind. Durch keine der verwendeten Methoden wird ein signifikantes Signal nachgewiesen. Die Maximum-Likelihood-Methode liefert jedoch eine kleinere statistische Unsicherheit. In dieser Methode ist das Verzweigungsverhältnis des Zerfalls B0 -&amp;gt; eta phi durch die obere Grenze BR (B0 -&amp;gt; eta phi) &amp;lt; 3.28 x 10^-6 (90%) gegeben. Dieser Wert enthält eine systematische Unsicherheit von 6.2%. Die angegebene obere Grenze ist mit aktuellen theoretischen Vorhersagen konsistent. Damit gibt diese Untersuchung keine Hinweise auf Wechselwirkungen, die nicht durch das Standardmodell der Elementarteilchenphysik beschrieben werden.