<p>This diploma thesis presents a preliminary study of the ratio of branching ratio r = BR(η → 3π⁰) / BR(η → π⁺ π^-π⁰). The experimental data used is collected by WASA-at-COSY which is a 4π sr detector optimised to detect light mesons and their decay products and is situated in Jülich, Germany.The focus of the work is to see how different reconstruction methods for the detected particles can alter both the measured values of the  branching ratios and the luminosity dependence of these branching ratios. The results show that for some of the methods, the measured branching ratios have a clear luminosity dependence. Depending on method, the extracted branching ratios vary differently. A few different methods have been studied, so the results provides a qualitative understanding of the behaviour of the measured branching ratios for different luminosities.</p>

This diploma thesis presents a preliminary study of the ratio of branching ratio r = BR(η → 3π0) / BR(η → π+ π- π0). The experimental data used is collected by WASA-at-COSY which is a 4π sr detector optimised to detect light mesons and their decay products and is situated in Jülich, Germany.The focus of the work is to see how different reconstruction methods for the detected particles can alter both the measured values of the  branching ratios and the luminosity dependence of these branching ratios. The results show that for some of the methods, the measured branching ratios have a clear luminosity dependence. Depending on method, the extracted branching ratios vary differently. A few different methods have been studied, so the results provides a qualitative understanding of the behaviour of the measured branching ratios for different luminosities.

Neutrino-nucleon scattering is an effective way to investigate the inner structure of the nucleon, to extract the Standard Model parameters and to explore heavy quarks production dynamics. In the last decades, several experiments have been constructed to study weak interactions of neutrinos with nucleons. One of them was CERN-WA95 experiment operated by the CHORUS collaboration. It is based on a hybrid detector with nuclear emulsion as a target followed by electronic devices. Nuclear emulsion provides three dimensional spatial information with an outstanding resolution of the order of one micron. Therefore, it is ideal to detect short-lived particles. A special technique has been developed to reconstruct events in the emulsion which allows to perform a detailed investigation of events such as charmed hadrons production by neutrinos. As a result, the backround in the selected charm sample is up to six times lower compared to similar experiments. Such a method also permits to make direct measurements of some quantities instead of model fittings. This thesis is devoted to the study of the muonic decays of charmed hadrons and their production in emulsion. Manual inspection of charm events gives a complete reconstruction of charm decay topology. The extraction of the inclusive muonic branching ratio is based on the ratios per number of charged daughters in charm decay. Such an approach allows to separetely measure the muonic branching ratios for neutral and charged charm particles. Finally, normalization of the events with a muon in the final state to the charged current events gives dimuon production rate which is found compatible with the previous experiments. On top of that, preliminary results are shown for Bjorken x distribution and for a direct measurement of the Vcd Cabbibo-Kabayashi-Maskawa matrix element.

Neutrino-nucleon scattering is an effective way to investigate the inner structure of the nucleon, to extract the Standard Model parameters and to explore heavy quarks production dynamics. In the last decades, several experiments have been constructed to study weak interactions of neutrinos with nucleons. One of them was CERN-WA95 experiment operated by the CHORUS collaboration. It is based on a hybrid detector with nuclear emulsion as a target followed by electronic devices. Nuclear emulsion provides three dimensional spatial information with an outstanding resolution of the order of one micron. Therefore, it is ideal to detect short-lived particles. A special technique has been developed to reconstruct events in the emulsion which allows to perform a detailed investigation of events such as charmed hadrons production by neutrinos. As a result, the backround in the selected charm sample is up to six times lower compared to similar experiments. Such a method also permits to make direct measurements of some quantities instead of model fittings. This thesis is devoted to the study of the muonic decays of charmed hadrons and their production in emulsion. Manual inspection of charm events gives a complete reconstruction of charm decay topology. The extraction of the inclusive muonic branching ratio is based on the ratios per number of charged daughters in charm decay. Such an approach allows to separetely measure the muonic branching ratios for neutral and charged charm particles. Finally, normalization of the events with a muon in the final state to the charged current events gives dimuon production rate which is found compatible with the previous experiments. On top of that, preliminary results are shown for Bjorken x distribution and for a direct measurement of the Vcd Cabbibo-Kabayashi-Maskawa matrix element.

Graduate

With the start of the Large Hadron Collider(LHC) at CERN, we will obtain a new understanding of the physics beyond our current limits. New discoveries will be made; but we will require a deeper understanding, which the LHC machine, being a hadron collider, will not be able to elucidate. Instead, we will need an e+e- collider to make precision measurements of the newly discovered phenomena. Electroweak symmetry breaking and the origin of fermion and boson masses are fundamental issues in our understanding of particle physics. The essential piece of electroweak symmetry breaking - the Higgs boson - will probably be discovered at the LHC. If there are one, or more, Higgs boson(s) precise measurements of all properties of the Higgs will be very important. In this thesis I present two measurements of Standard Model Higgs boson properties in the context of the International Linear Collider (ILC) at √s = 500 GeV, using the proposed International Linear Detector (ILD). First a performance study of ILD to measure the branching ratios of the Higgs boson with mH = 120 GeV, where the Higgs boson is produced with a Z-boson via the Higgsstralung process, and the Z decays into e+e- or μ+μ-. It will also be essential to study the Higgs Yukawa coupling. Therefore, in the second part of this thesis, I present a study of e+e- → tt¯H with the aim of making a direct measurement of the the top-Higgs coupling, using the semi-leptonic nal state and mH of 120 GeV. I show that the top-Higgs coupling can be measured with an accuracy of better than 28%.

Nessa tese procuramos o decaimento radioativo raro - -. É um dos resultados da experiência E761 realizada no Proton Center do Fermilab, usando o feixe de híperons carregados com momento de 377 GeV/c. Medimos a fração deste feixe que é constituída de -, sendo esta (3,9 ±0,3)X10-5. Não encontramos sinal do decaimento radiativo - - e determinamos um novo limite superior de 7,5X 10-4 (90% CL). / In this thesis we have searched for the rare hyperon radiative decay - -. It is one of the results of E761 experiment which was realized at Fermilab Proton Center using a 377 GevIc charged hyperon beam. We measure the - beam fraction, which is (3.9 ± 0.3)x10-5 at the start of the decay region. No signal for the radiative decay was found and we determine a new upper limit of 7.5 x 10-4 at 90% CL for the - - branching ratio.

>Magister Scientiae - MSc / An increasing number of measurements reveal the presence of a low-energy enhancement in the gamma-ray strength function (GSF). The GSF, which is the ability of nuclei to absorb or emit rays, provides insight into the statistical properties of atomic nuclei. For this project the GSF was studied for 74Ge which was populated in the reaction 74Ge(p,p')74Ge* at a beam energy of 18 MeV. The data were collected with the STARS-LIBERACE array at Lawrence Berkeley National Laboratory. Silicon detector telescopes were used for particle identi cation and rays in coincidence were detected with 5 clover-type high-purity germanium detectors. Through the analysis particle- - coincidence events were constructed. These events, together with well-known energy levels, were used to identify primary rays from the quasicontinuum. Primary rays from a broad excitation energy region, which decay to six 2+ states could be identi ed. These states and the associated primary rays are used to measure the GSF for 74Ge with the Ratio Method [1], which entails taking ratios of e ciency-corrected primary -ray intensities from the quasicontinuum. Results from the analysis of the data and focus on the existence of the low-energy enhancement in 74Ge will be discussed. The results are further discussed in the context of other work done on 74Ge using the ( , ') [2], (3He,3He') [3] and ( , ') [4] reactions.

Nessa tese procuramos o decaimento radioativo raro - -. É um dos resultados da experiência E761 realizada no Proton Center do Fermilab, usando o feixe de híperons carregados com momento de 377 GeV/c. Medimos a fração deste feixe que é constituída de -, sendo esta (3,9 ±0,3)X10-5. Não encontramos sinal do decaimento radiativo - - e determinamos um novo limite superior de 7,5X 10-4 (90% CL). / In this thesis we have searched for the rare hyperon radiative decay - -. It is one of the results of E761 experiment which was realized at Fermilab Proton Center using a 377 GevIc charged hyperon beam. We measure the - beam fraction, which is (3.9 ± 0.3)x10-5 at the start of the decay region. No signal for the radiative decay was found and we determine a new upper limit of 7.5 x 10-4 at 90% CL for the - - branching ratio.

Results of the search for the rare decay $B_s^0 \to \mu^+ \mu^-$ using data collected by the D0 detector at the Fermilab Tevatron collider are presented. This analysis covers the full Run II data set, corresponding to approximately 10.4~fb$^{-1}$ of integrated luminosity in $p\bar{p}$ collisions at a center of mass energy of 1.96 TeV. The analysis used new variables and a multivariate technique to improve the background reduction. After seeing fewer events than expected from background, a new Tevatron best observed limit was set on the branching fraction of the decay at $\cal{B}$($B_s^0 \to \mu^+ \mu^-$) $< 15 \times 10^{-9}$ ($12 \times 10^{-9}$) at the 95\% (90\%) C.L.