This thesis describes a search for the rare radiative decay of a B meson to two photons. where the charged congugate mode is implied throughout. These decays are highly suppressed in the Standard Model where the branching fraction is expected to be of order 10^-8. In some new physics scenarios this could be enhanced by up to an order of magnitude to 10^-7. Therefore an observation of a significant signal above the Standard Model prediction could be a sign of new physics. The search for this rare decay was performed using the data collected with the BaBar detector at the SLAC National Accelerator Laboratory PEP-II storage ring operating at the Upsilon(4S) resonance. The analysis uses a dataset with an integrated luminosity of 425.7 fb-1 corresponding to 467 million BB pairs. A signal yield of 21.3 +12.8 -11.8 events with a significance of 1.88 sigma was measured using an unbinned extended maximum likelihood fit. An upper limit on the branching fraction is set at the 90% confidence level of less than 3.2 times 10^-7. This is about two times more stringent than the best upper limit of less than 6.2 times 10^-7 published by the Belle collaboration. / text

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21564号 / 理博第4471号 / 新制||理||1642(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)准教授 市川 温子, 教授 鶴 剛, 教授 中家 剛 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

要旨ファイルを2017-04-17に差替え / 京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19502号 / 理博第4162号 / 新制||理||1598(附属図書館) / 32538 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 中家 剛, 教授 谷森 達, 准教授 成木 恵 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19882号 / 理博第4209号 / 新制||理||1605(附属図書館) / 32959 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 中家 剛, 教授 谷森 達, 教授 永江 知文 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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An angular analysis of the rare decay B0 → K∗ (K+ π− )µ+ µ− is presented. The study is based on a data sample from pp collisions at centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider which corresponds to an integrated luminosity of 20.3 fb−1 . An extended unbinned maximum-likelihood fit of the decay angular distribution is used to measure the CP-averaged angular observables FL, S3, S4, S5, S7 and S8 and the cor- responding form-factor independent observables P1, P4, P5, P6 and P8. The measurements are performed in the region 0.04 GeV2 < q2 < 6 GeV2 , where q is the dimuon invariant mass. The results are in agreement with the Standard Model predictions and com- patible with measurements published by other experiments. The most signifi- cant deviations are observed for parameters P4, P5 at the level of 2.7 standard deviations and for P8 which is 1.9 standard deviations away from one of the predictions. The P5 deviation in bin 4 GeV2 < q2 < 6 GeV2 is consistent with the one reported by the LHCb collaboration. The second part of this work shortly summarises the operation of the ATLAS Semiconductor Tracker, testing of the prototype module for the Inner Tracker strip upgrade, and the monitoring of non-collision background which was devel- oped as a part of this thesis.

A comparative study is done on the Mini Drift Chamber (MDC) and the Scintillating Electromagnetic Calorimeter (SEC), two main components of the WASA detector. The purpose of the study is to determine the most effective way to calculate the mass of the η−meson by determining the invariant mass of the final products in the η → e+e− decay. When calculating the invariant mass of the lepton pair the distribution from the MDC had a standard deviation of σMDC = (4.212 ± 0.080) · 10−2 GeV/c2 and from the SEC σSEC = (3.563±0.011)·10−2 GeV/c2. To get a precise measurement, events with a lepton scattering at a polar angle below 30◦ have to be rejected, and to achieve highest precision, it is favorable to use the SEC for momenta above 0.28 GeV/c and the MDC below, respectively. In this study, a combined method is developed which results in an invariant mass resolution of σMix = (3.341±0.012)·10−2 GeV/c2. Thus, the combined method gives a small improvement compared to using the SEC alone, but a considerable improvement compared to using only the MDC.

This thesis studies the rare decay η' → π+π-e+e- using Monte Carlo simulations and data from the BES-III detector in Beijing, China. The branching ratio of the reaction was measured at BES-III in 2013 using a data set of 225×106 J/Ψ events. This work lays the groundwork for an updated branching ratio measurement using the full data set of 1.3×109 J/Ψ and determines a potential CP-violating asymmetry in the angle between the decay planes of the π+π-- and e+e--pairs. A total of 2558 signal events are observed after cuts, and the asymmetry parameter is determined to be  Aφ = (1.96 ± 1.97stat.± 0.4syst. ) × 10-2. The result is consistent with zero within the uncertainty.

Les désintégrations de quark $b$ rares interviennent principalement via des courant neutres changeant la saveur, (Flavor Changing Neutral Current, FCNC en anglais). Le modèle Standard n'autorise les courants qu'au niveau des boucles. Ces processus FCNC sont sujets \`a une suppression de GIM conduisant à des processus rares. Par conséquent les désintégration $b to s$ sont de très bon outils pour la recherche de phénomène de Nouvelle Physique au delà du Modèle Standard. Cette thèse présente l'analyse angulaire de la désintégration $B^0\to K^{*0}\mu^+\mu^-$ avec l'ensemble des données collecté par l'expérience lhcb durant le run I du lhc. La complète série des observable angulaires a été mesuré via un ajustement d'une fonction de vraisemblance, gr$\hat{\rm a}$ce à une sélection amélioré et les 3 fb$^{-1}$ de donné collecté en 2011 et 2012 par lhcb. Par ailleurs, l'analyse du rapport $R_{K^*}$ est également présenté et les résultats sont attendu pour la fin de l'année 2015. / Rare beauty decays proceed mostly through the $b\to s$ Flavor Changing Neutral Current, which is possible only at loop level in the Standard Model. These FCNC processes are subject to GIM suppression leading to a rare decay. Therefore the $b\to s$ processes are good tools to look for New Physics phenomenon beyond the Standard Model. New Physics particle could become detectable by causing deviation from the Standard Model predictions for observables such as angular observables, branching ratio or CP asymmetries. This thesis present the angular analysis of the $B^0\to K^{*0}\mu^+\mu^-$ decay with the whole dataset collected by lhcb during the first run of the lhc. The full set of the angular observables has been measured through a maximum likelihood fit, thanks to an improved selection and the 3 fb$^{-1}$ of data collected in 2011 and 2012 by lhcb. In addition, the analysis on the measurement of the ratio $R_{K^*}$ has also been presented and the results are expected by the end of 2015.