Heavy quark decays provide a very advantageous investigation to test the Standard Model (SM). Recently, promising experiments with b quark, as well as the analysis of the huge data sets produced at the Large Hadron Collider(LHC) experiment, have led to an increasing study and sensitive measurements of relative b quark decays. In this thesis, a preliminary study is presented for the first time observation of the B+ → ψ(2S)φK+ with a statistical significance above 5 standard deviations using proton-proton collisions at √s = 8 TeV collected with CMS detector at LHC. The data sample, selected on the basis of the dimuon decay mode of the ψ(2S), corresponds to an integrated luminosity of 19.6 fb−1. A total of 140±15 B+ → ψ(2S)φK+ events have been observed. The branching fraction of B+ → ψ(2S)φK+ is measured relative to B+ → ψ(2S)K+, whose absolute branching fraction (BF) is known. The ratio is converted to an absolute branching fraction of B+ → ψ(2S)φK+, including systematics which is determined to be (4.0 ± 0.4(stat) ± 0.6(syst) ± 0.1(BR)) × 10−6, where the third uncertainty is due to imprecise knowledge of BF. The upper limit of the fraction of B+ → ψ(2S)(non−φ)K+ component in the selected B+ → ψ(2S)K+K−K+ channel is found to be 26% at 95% confidence level.

At the dawn of the Large Hadron Collider era, the Brout-Englert-Higgs mechanism remains the most appealing theoretical explanation of the electroweak symmetry breaking, despite the fact that the associated fundamental scalar boson has escaped any direct detection attempt. In this thesis, we consider a particular extension of the minimal Brout-Englert-Higgs scalar sector implemented in the Standard Model of strong and electroweak interactions. This extension, which is a specific, "twisted", realisation of the generic two-Higgs-doublet model, is motivated by a relative phase in the definition of the phenomenologically successful CP and custodial symmetries. Considering extensively various theoretical, indirect and direct constraints, this model appears as a viable alternative to more conventional scenarios like supersymmetric models, and gives grounds to largely unexplored possibilities of exotic scalar signatures at present and future collider experiments.

This thesis describes the research I did during my Master's study. I investigated the stau-neutralino coannihilation region of the Mirage Mediation Model at the Large Hadron Collider (LHC). By constructing five kinematic observables at the LHC, the masses of supersymmetric particles (sparticles) were determined. The Mirage Mediation Model parameters were determined from the sparticles' masses. This is the first time to establish the Mirage Mediation Model at the LHC. All these techniques can be applied to other coannihilation regions of the Mirage Mediation Model and other supersymmetry (SUSY) models.

Following the discovery of the Higgs-like boson at the Large Hadron Collider, there is demand for precision measurements on recent findings. The Compact Linear Collider, CLIC, is a candidate for a future linear electron-positron collider for such precision measurements. In CLIC, the beams will be brought to collisions in the multi-TeV regime through high gradient acceleration with high frequency RF power. A high intensity electron beam, the so-called drive beam, will serve as the power source for the main beam, as the drive beam is decelerated in special structures, from which power is extracted and transfered to the main beam. When the drive beam is decelerated the beam quality deteriorates and the momentum spread increases, which makes the beam transport challenging. Dedicated diagnostics to monitor the momentum profile along each bunch train and transverse profile diagnostics will be needed to guarantee the reliability of the decelerator and consequently the power source of the main beam acceleration. A test facility, CTF3, has been constructed at CERN to validate key technical aspects of the CLIC concept. The beam quality in the decelerator will be investigated in the test beam line, TBL, where several power extraction structures reduce the drive beam energy by up to 55%. At the same time, the single-bunch rms energy spread grows from the initial value of 1% to almost 6%. To monitor the parameters of such a beam is challenging but crucial for the optimization of the beamline. In this thesis we report on progress made on adapting generally used methods for beam profile measurements to the demanding conditions of a wide momentum profile. Two detector technologies are used for measuring transverse profile and momentum profile and we discuss the performance of these instruments, in the view of the large momentum spread and with the outlook towards equivalent beam profile monitors in the CLIC decelerator.

The ATLAS Experiment is one of the four large detectors located at the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland. In summer 2008, ATLAS is expected to start collecting data from proton-proton collisions at 14 TeV centre-of-mass energy. In the centre of the detector, the reconstruction of charged particle tracks is performed by silicon and drift tube based sub-detectors. In order to achieve the ATLAS physics goals the resolutions of the measured track parameters should not be degraded by more than 20% due to misalignment. Thus, the relative positions of the silicon detector elements have to be known to an accuracy of about 10 micrometers in the coordinate with the best measurement precision. This requirement can be achieved by track based alignment algorithms combined with measurements from hardware based alignment techniques. A robust track based alignment method based on track residual and overlap residual optimisation has been developed and implemented into the ATLAS offline software framework. The alignment algorithm has been used to align a test beam setup and also part of the final ATLAS detector using cosmic ray muons. Several simulation studies showed that the algorithm will be able to align the full detector with collision data. In addition to detector misalignments, limitations in the knowledge of the proton structure are going to affect physics discoveries at the LHC. Therefore, parton distribution uncertainties in high-mass Drell-Yan processes have been determined. This study includes the analysis of the forward-backward asymmetry. It has been performed on the level of next-to-leading order in both, Monte Carlo simulation using k-factors and parton distribution functions. This analysis is crucial for new physics searches with the ATLAS detector.

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This thesis presents a measurement of the effective B0s decay width, ΓFS, from a single exponential fit to the flavour-specific decay channel B0s → D-s π +. This measurement is based on an integrated luminosity of 340 pb-1 recorded by LHCb in 2011 at a center of mass energy of 7TeV. The dataset is divided into two exclusive selections. B0s → D-s (( ϕ →K-K+) π-)π + only has a significant background contribution arising from combinatorial background, and the modelling of this is determined entirely by the data. B0s → D-s ((K-K* (892)0 → K+ π-))π + has a larger contribution from combinatoric and mis-identified background and provides an alternative measurement. A simultaneous fit for the effective B0s decay width is performed to both the datasets leading to the result: ΓFS = 0:668 ± 0:017 ± 0:031 ps-1 The result is then combined with information from the LHCb B0s → J/ψØ analysis leading to an improved measurement of the average B0 s decay width: Γs = 0:666 ± 0:010 ± 0:031 ps-1

The search for the Higgs boson has been a cornerstone of the physics program at the Large Hadron Collider in Geneva Switzerland. The ATLAS experiment successfully discovered the Higgs using the so-called ‘Golden Channels’ of H0 -> gamma gamma and H0 -> ZZ(∗) using data samples collected during the 2011 and 2012 run periods. In order to check if the discovered Higgs is consistent with purely Standard Model behaviour, it is necessary to further confirm the existence of the Higgs in each production mode and decay channel predicted by the Standard Model. For this dissertation, a search for the Higgs was conducted using the H0 -> b bbar decay channel, where the Higgs is produced by the inverse pair decay of two weak bosons exchanged by a scattered quark pair, also known as Vector Boson Fusion (VBF). This analysis uses data samples collected during the 2011 run period by the ATLAS detector totalling 4.2 /fb of proton-proton collisions at sqrt(s) = 7 TeV. No excess of events above background expectation is observed and 95% confidence level upper limits on the Standard Model Higgs cross section times branching ratio, sigma(VBF) x BR(H0 -> b bbar), are derived for Higgs masses in the range 115 < mH < 130 GeV. An observed 95% confidence level upper limit of 18.7 times the Standard Model cross section is obtained for a Higgs boson mass of 125 GeV. / Graduate / 0798