Despite decades of theoretical and experimental investigation, the fundamental interactions between nucleons remains poorly understood. While the strong interaction is responsible for binding quarks into nucleons, and nucleons into nuclei, there is no consistent description of these processes. At the low energies where nucleon binding occurs, the interactions are in principle calculable from quantum chromodynamics, but the required non-perturbative calculations are not possible. Instead, different models have been created to describe different phenomena. These models require experimental input to constrain them. As the expected weak interaction effects are not seen in the strangeness-conserving systems as have been seen in other systems, it is believed that the strong interaction interferes with the weak interaction. Therefore by measuring parity-violating observables that occur due to the weak interaction, information can be gained about the strong interaction. The NPDGamma and n3He experiments are two complementary experiments that measured a parity violating observables in a few nucleon system. They ran on the Fundamental Neutron Physics Beamline at the Spallation Neutron Source. The NPDGamma experiment measured the parity violating directional asymmetry in the gamma ray's emission direction after polarized cold neutron capture on a liquid parahydrogen target using an array of 48 CsI detectors. The n3He experiment measured the parity violating directional asymmetry in the proton emission direction after polarized cold neutron capture on a gaseous $^{3}$He target. The capture occurs inside an ionization chamber that measures the proton emission direction. Both experiments have completed data taking with data analysis in an advanced state. These experiments should be able to be used with a number of already existing experimental results to constrain the models. I designed and assembled a pair of $^{3}$He ionization chambers that were used as beam monitors during the experiments. Using the lessons learned from the beam monitors, I then designed and assembled the ionization chamber that is the combined target and detector for the n3He experiment. The monitors and target chamber were examined to determine their charge collection properties and linearity after installation. One of the monitors was calibrated to determine the neutron flux from the output current. / February 2017

Doctor of Philosophy / Department of Physics / Yurii Y. Maravin / This thesis presents the first study of a rare production of Z boson in association with two photons (Zγγ), where the Z boson decays into a pair of muons or electrons, by proton-proton collisions at the Large Hadron Collider (LHC). This study uses full data samples that have been collected with the Compact Muon Solenoid (CMS) detector in 2012 with a center of mass energy of 8TeV, corresponding to an integrated luminosity of 19.7 fb⁻¹. The Zγγ production cross section is measured within a fiducial region defined by two leptons with two photons where transverse momentum over 15 GeV and distance between gamma and lepton above 0.4. Using the obtained samples, the Zγγ cross section is measured to be: 12.6 ±1.6 (stat.) ± 1.7 (syst.) ± 0.3 (lumi.) fb. where stat., syst., and lumi. denote the statistical uncertainty, systematic uncertainty, and the uncertainty in integrated luminosity, respectively. This result is in an excellent agreement with the theoretical prediction of 13.0 ± 1.5 fb.

Many interesting physical processes produce non-interacting particles that could only be measured using the missing transverse momentum. The increase of the proton beam intensity in the Large Hadron Collider (LHC) provides sensitivity to rare physics processes while inevitably increasing the number of simultaneous proton collisions in each event. The missing transverse momentum (MET) is a variable of great interest, defined as the negative sum of the transverse momentum of all visible particles. The precision of the MET determination deteriorates as the complexity of the recorded data escalates. Given the current complexity of data analysis, a new algorithm is developed to effectively determine the MET. Several well-understood physics processes were used to test the effectiveness of the newly designed algorithm. The performance of the new algorithm is also compared to that of the standard algorithm used in the ATLAS experiment. / Graduate

A dissertation submitted in fulfillment of the requirements for the degree of Master of Physics in the School of Physics November 1, 2017. / The ATLAS detector at the Large Hadron Collider (LHC) at CERN is undergoing upgrades to its instrumentation, as well as the hardware and software that comprise its Trigger and Data Acquisition (TDAQ) system. The increased energy will yield larger cross sections for interesting physics processes, but will also lead to increased artifacts in on-line reconstruction in the trigger, as well as increased trigger rates, beyond the current system’s capabilities. To meet these demands it is likely that the massive parallelism of General-Purpose Programming with Graphic Processing Units (GPGPU) will be utilised. This dissertation addresses the problem of integrating GPGPU into the existing Trigger and TDAQ platforms; detailing and analysing GPGPU performance in the context of performing in a high-throughput, on-line environment like ATLAS. Preliminary tests show low to moderate speed-up with GPU relative to CPU, indicating that to achieve a more significant performance increase it may be necessary to alter the current platform beyond pairing suitable GPUs to CPUs in an optimum ratio. Possible solutions are proposed and recommendations for future work are given. / LG2018

A basic assumption in fundamental physics is that equal amounts of matter and antimatter were created after the Big Bang. When particles and antiparticles collide, they annihilate, i.e. disappear and produce photons. Nevertheless, the universe consists mainly of matter today. To explain why all matter did not disappear, violation of CP symmetry beyond the Standard Model is required. CP symmetry means that the laws of physics are the same if particles are interchanged with antiparticles and spatial coordinates of all particles are mirrored. CP symmetry is relatively poorly tested in baryon decays. A new method to study CP symmetry in hyperon-antihyperon pairs has been developed at Uppsala University. Hyperons are baryons with one or more strange quarks. The method allows determining the decay asymmetry parameters of the hyperon and antihyperon separately if the hyperon-antihyperon pair is polarized. If any significant difference between the magnitudes of these parameters is found, the process is CP violating. The particle physics experiment BESIII in China is a suitable experiment to conduct this kind of measurements because it is a high precision experiment and has collected large data samples of hyperon-antihyperon pairs. The goal of this project was to study statistical precisions of the physics parameters that can be obtained with the new method in cases of J/ψ meson decaying into ΛΛ, Σ+Σ− and Σ0Σ0. High statistical precision is required to detect CP violation, because CP violating processes are, if they exist, expected to be rare. The main focus was to study the process e+e− → J/ψ → Σ0Σ0 → ΛγΛγ → pπ−γpπ+γ. In this process, CP symmetry can be tested in two decay processes: electromagnetic decay Σ0 → Λγ and weak decay Λ → pπ−. Only the asymmetry parameter of Λ → pπ− was studied. The study served as a validity check of the new method and ongoing analyses at BESIII. The statistical precision was studied by simulations: Monte Carlo data samples were created and then a maximum-log-likelihood fit was applied to the samples. An important component when determining the asymmetry parameters turned out to be the relative phase ∆φJ/ψ. The relative phase is one of the parameters used for determining the relation between the electric and magnetic form factors. ∆φJ/ψ is also related to the polarization of the hyperon-antihyperon pair. The study showed that the value of ∆φJ/ψ has a large impact on the uncertainties of the hyperon and antihyperon asymmetry parameters. A low value of ∆φJ/ψ resulted in high uncertainties and strong correlations between the asymmetry parameters. The formalism is different for different processes, which affects the uncertainties as well. The formalism used for the Σ0Σ0 process gives poorer parameter precision of the asymmetry parameter related to the Λ → pπ− decay than the formalism used for the ΛΛ process. Therefore, the ΛΛ process is a much more suitable process for CP studies of the Λ → pπ− decay. / Ett grundantagande inom den fundamentala fysiken är att lika stora mängder av materia och antimateria skapades efter Big Bang. När partiklar och antipartiklar kolliderar, annihilerar de, dvs försvinner och producerar fotoner. Trots detta består dagens universum huvudsakligen av materia. För att förklara varför all materia inte försvann krävs ett brott mot CP-symmetrin bakom standardmodellen. CP-symmetrin innebär att fysikens lagar är desamma om man byter partiklar mot antipartiklar och speglar partikelns rumsliga koordinater. CP-symmetri i baryonsönderfall är relativt dåligt testad. En ny metod för att studera CP-symmetrin har utvecklats vid Uppsala universitet för hyperon-antihyperon par. Hyperoner är baryoner med en eller fler särkvarkar. Metoden gör det möjligt att bestämma asymmetriparametrar hos hyperon- och antihyperonsönderfall separat om hyperonantihyperonparet är polariserat. Om en signifikant skillnad mellan värden av dessa parametrar upptäcks, är processen CP-brytande. Partikelfysikexperimentet BESIII i Kina är ett lämpligt experiment för sådana här mätningar eftersom det är ett högpresicionsexperiment och har dessutom samlat in stora mängder data av hyperon-antihyperonpar. Målet för detta projekt har varit att studera de statistiska precisioner av fysikparametrar som kan nås när man använder den nya metoden i de fall där J/ψ mesonen sönderfaller till ΛΛ, Σ+Σ− och Σ0Σ0. Hög statistisk precision behövs för att upptäcka CP-brott, eftersom CP-brytande processer, om de existerar, är relativt sällsynta. Huvudfokuset var att studera processen e+e− → J/ψ → Σ0Σ0 → ΛγΛγ → pπ−γpπ+γ. I denna process kan CP-symmetri testas för två sönderfallsprocesser: det elektromagnetiska sönderfallet Σ0 → Λγ och det svaga sönderfallet Λ → pπ−. I denna rapport studerades bara asymmetriparametrarna av Λ → pπ−. Detta arbete har fungerat som validitetskontroll av den nya metoden och pågående analyser på BESIII. Den statistiska precisionen undersöktes med simuleringar: Monte Carlo datamängder skapades och sedan en maximum-log-likelihood-anpassning av datan genomfördes. En viktig komponent i bestämningen av asymmetriparametrarna visade sig vara den relativa fasen, ∆φJ/ψ. Den relativa fasen är en av de parametrar som används för att bestämma relationen mellan de elektriska och magnetiska formfaktorer. ∆φJ/ψ är också relaterad till hyperonens hyperon-antihyperonparets polarisation. I forskningsprojektet visades att ∆φJ/ψ har en stor inverkan på osäkerheterna av hyperon- och antihyperonasymmetriparametrarna. Ett lågt värde av ∆φJ/ψ resulterade i stora osäkerheter och starka korrelationer mellan asymmetriparametrarna. Formalismen är annorlunda för olika processer, vilket också påverkar osäkerheterna. Formalismen som används för Σ0Σ0-processen ger sämre parameterprecision av asymmetriparametern kopplad till sönderfallet Λ → pπ− än formalismen som används för ΛΛ-processen. Därför är ΛΛ-processen en mycket lämpligare process för att testa CP-symmetrin i Λ → pπ− sönderfallet.

Following the announcement of the discovery of a new particle on the 4th of July 2012 at the ATLAS and CMS experiments at the LHC, many efforts were needed for the understanding of its properties and to discern whether it is the Standard Model Higgs boson. The research presented in this thesis is based on the H → ZZ(*) → 4l decay channel. Three main contributions are discussed: the Standard Model Higgs boson mass measurement, the search for a heavy Higgs boson, and lastly, the implementation of a kinematic likelihood fitter as a new approach to improve the invariant mass resolution of the final states. The Standard Model Higgs boson mass measurement is presented. The measured mass is 124:51± 0:52(stat)± 0:06(syst) GeV for the combined data taken during 2011 and 2012 (4:6 fb-¹ at 7 TeV and 20:7 fb-¹ at 8 TeV). Contributing to the mass measurement, a tool was developed to validate the model used by generating several pseudo datasets from Monte Carlo samples and fitting them with the profile likelihood. The results show that the model is correct and only small deviations are seen in the parameters of interest, mH, and the signal strength, μ. Studies in the asymptotic limit show that these deviations are a symptom of low statistics in some of the final states. The search for a heavy Higgs boson is presented as well. No significant excess of events over the Standard Model prediction is found. A simultaneous fit to the profile likelihood gives 95% confidence level upper limits on the production cross-section of a heavy Higgs times the branching ratio to Z boson pairs in the mass range from 140 GeV to 1 TeV. Contributing to this search, a pseudo dataset, called Asimov dataset, is created from the Monte Carlo samples to test the profile likelihood fits and validate the model used. The results show that fit the model is correct. In addition, the limits are also interpreted in the context of Type I and Type II Two Higgs Doublet Models (2HDM). Finally, a Kinematic Likelihood Fitter (KLFitter) is studied and used to constrain the Z boson mass as an alternative to the standard tool used for the 2011 and 2012 measurement. This affects the distribution of the invariant mass, m4l, from which the Higgs boson mass is inferred. Small improvements are seen in the invariant mass resolution when higher hypothetical Higgs boson masses are considered.

Two measurements of the Cabibbo-Kobayashi-Maskawa angle &gamma; using B &rarr; DK and B⁰ &rarr; DK^&ast;0 decays are presented in this thesis. The subsequent D meson decays to the K_S⁰&pi;⁺&pi;^− and K_S⁰K⁺K^− final states are studied using a binned Dalitz plot analysis. The D strong-phase variation over the Dalitz plot is taken from measurements performed at the CLEO-c experiment, making the analysis independent of a model to describe the D decay amplitude. Both measurements are performed using proton-proton collision data collected by the Large Hadron Collider beauty (LHCb) experiment in 2011 and 2012, corresponding to an integrated luminosity of 3 fb^−1 at centre-of-mass energies &radic;s = 7 TeV and 8 TeV. The value &gamma;= (62 ⁺¹⁵<sub style='position: relative; left: -1.7em;'>−14</sub>)° is measured using B⁰ &rarr; DK^&ast;0 decays and &gamma; = (71 ± 20)° is measured using B⁰ &rarr; DK^&ast;0 decays, with a second solution for each value corresponding to &gamma; + 180°. The measurements are consistent with the world average value of &gamma;.

This thesis describes the measurement of inclusive heavy flavor jet suppression in collisions between two lead nuclei with the center of mass energy per nucleon-nucleon pair of 2.76 TeV with the ATLAS detector at the Large Hadron Collider (LHC). The measurement of the heavy flavor jets and b-jet quenching at the LHC is important in the path towards the understanding of QGP. Parton showers initiated by heavy quarks are expected to be sensitive to the medium in a different way as the large quark mass suppresses the medium-induced radiation. This results in a different interplay between radiative and collisional energy loss. Therefore the analysis of the properties of jet associated with b hadrons (b-jet) is useful in understanding energy loss in the QGP. The inclusive b-jet suppression R AA has been measured using muons in jets, where a b-jet corresponds to a jet with at least one muon clustered with the anti-k t algorithm with parameter R = 0.2. The b-jets of p T between 30 GeV - 150 GeV are identified by the semileptonic decay of beauty hadrons. Muons originating from background sources, primarily Charm hadrons, pion and kaon decays, have been removed from the analysis using template fits to the distribution of a quantity(p T^rel) capable of statistically distinguishing between signal and background. The measured nuclear modification factor R AA has been presented in different centrality bins as a function of the b-jet transverse momentum p T.The results of R AA indicate that the yield of the most central event (0-10%) experiences more suppression compared to the most peripheral event (60-80%) by a factor of approximate 2.

This thesis presents the first measurement of the d*(2380) (hexaquark) electromagnetic coupling, extracted from the deuteron photodisintegration (~γd → d* → ~np) reaction. The experiment was carried out at the Mainzer Microtron (MAMI) facility in the Institut für Kernphysik in Mainz, Germany. A racetrack microtron at the MAMI facility provided a 1557 MeV longitudinally polarised electron beam. This electron beam was directed onto a thin radiator to produce a bremsstrahlung photon beam. Diamond and amorphous (metallic) radiators were used to produce linearly and circularly polarised photons respectively. The produced bremsstrahlung photon beam was energy 'tagged' with a resolution of ~4 MeV over the photon-energy range of 150-1400 MeV using the Glasgow Photon Tagger. The tagged photons were incident on a 10 cm long liquid deuterium target. This target was surrounded by a new nucleon recoil polarimeter apparatus and placed within the Crystal Ball calorimeter at MAMI. An array of PbWO4 and BaF2 detectors (TAPS) was used to provide calorimetry at forward angles. The newly constructed large acceptance recoil polarimeter measures the polarisation of the nucleons in the final state. The combination of this new apparatus with the polarised photon beam facility gives access to a number of single and double polarisation observables. The photon beam asymmetry, Σ, and the double polarisation observable, Cx', were examined in measurements of the reaction d(→γ,→n→p) over a large range of energies with a close to full angular coverage. The observable Cx' is determined for the neutron produced in deuteron photodisintegration for the first time. The new data constrains mechanisms of deuteron photodisintegration and assesses the existence and contribution of the d*(2380) resonance.

Estágio realizado no CERN e orientado Eva Sanchez-Corral Mena / Tese de mestrado integrado. Engenharia Informática e Computação. Faculdade de Engenharia. Universidade do Porto. 2008