Next-to-minimal super-symmetric extensions of the Standard Model (SM) predict the existence of several non-SM like Higgs bosons. The process pp→a1h±→4b+W involves the production and the decay of a spin-0 charged Higgs boson and a CP-odd Higgs boson a1 which can have a sizable cross section in the NMSSM. The invariant masses of these intermediate bosons can be reconstructed from the four momenta of the final state particles using mass minimization algorithms. This thesis presents a cut-based analysis of two mass scenarios and specialized algorithms that are capable of recovering the signal in a large background arising from Standard Model processes such as ttbar. The analysis is tested with a realistic ATLAS detector simulation investigating trigger efficiencies and probing several jet reconstruction algorithms.

Kaluza-Klein theories generally in $(4+D)$ and more specifically in five dimensions are reviewed. The magnetic monopole solutions found in the Kaluza-Klein theories are generally reviewed and their generalizations to Anti-de Sitter spacetimes are discussed.

The OPERA experiment is designed to perform first direct observation of $nu_{tau}$ appearance in an almost pure $nu_{mu}$ beam. The OPERA detector is a hybrid set-up which combines a lead/emulsion target with various electronic detectors. It is located in Gran Sasso Laboratory (LNGS), 730 km away from CERN where neutrino beam is produced. A good electron identification in the ECC brick would also allow OPERA to search for $nu_{mu}rightarrownu_{e}$ oscillations. We have studied electron identification in the Emulsion Cloud Chamber (ECC) brick which was exposed to CERN SPS H4 electron beam. Emulsion scanning was performed in LNGS scanning laboratory. FEDRA framework was used for the data analysis. In total, we have found 30 electron showers in the brick. The characteristics of each shower have been studied. The background base-track contamination in the shower was estimated as $20pm 4$. This is mainly due to shower overlap of electrons and passing through cosmic rays.

The OPERA experiment is designed to search for nu-tau appearance in almost pure CERN-SPS nu-mu beam. The OPERA detector is placed in the Gran Sasso underground laboratory which is 730 km away from CERN. It is a hybrid set-up which combines a lead/emulsion target with various electronic detectors. The detector is composed of two super modules(SM) which contains about 150,000 ECC bricks. Each of the brick is obtained by stacking 56 lead plates with 57 emulsion films. Behind the each brick, an emulsion film doublet, called Changeable Sheet (CS) is attached in order to confirm tracks produced in neutrino interactions. The CS requires very low background track density in order to ensure the expected performance in the experiment. The background tracks in CS can be erased by a special treatment called as refreshing. A refreshing facility was constructed in the LNGS laboratory. The METU group has participated in the construction of the facility and the production of the CS films from the beginning. The main steps of emulsion refreshing and the test results on emulsion quality after the refreshing will be discussed. A Monte Carlo simulation is performed in order to estimate background to nu-mu to nu-tau oscillation due to D0 production and decay in the ECC brick. It is found that this background is significant for the short decay path topology of the tau lepton.

We consider three distinct categories of supersymmetric scenarios with heavy scalars and light gauginos. First, we investigate the SO(10) SUSY GUTs, and locate MSSM parameter space regions that satisfy GUT scale Yukawa unification, which is a distinct feature of these models. Then taking example SO(10) cases, we perform a Monte Carlo study with toy detector simulation at 14 TeV at the LHC on the no $met$ leptonic channels 2,3 leptons + $ge$4 jets and show that discovery is possible with $sim$1 fb$^{-1}$ of integrated luminosity. We also demonstrate the feasibility of invariant mass endpoint measurements for $sim$100 fb$^{-1}$. Furthermore, in a cosmological context, we propose that SO(10) scenarios with excess neutralino relic abundance can be made WMAP-compatble by assuming neutralino decays to axinos, and show that there are various axino/axion cold and warm dark matter admixtures which can be consistent with non-thermal leptogenesis requirements for the thermal re-heat temperature. Afterwards we complement the SO(10)s with the string-inspired G$_2$-MSSM and focus point mSUGRA scenarios and perform a full simulation search of these at $sqrt{s} =$ 14 TeV at the LHC with the CMS detector where the main production mechanism is through gluino pair production and the final states are cheracterized by all-hadronic topologies (including $b$s and $t$s). Through the design of six prototype all-hadronic selection paths and using the CMS High Lever Trigger paths with highest significance (including the $b$-enriched ones), we find that all but one model benchmarks are accessible with 100 pb$^{-1}$ integrated luminosity. We present the results as a function of the gluino mass considering the major detector systematic effects.

Quantum Chromodynamics(QCD) is part of the Standard Model(SM) that describes the interaction of fundamental particles. In QCD, due to the fact that strong coupling constant is large at low energies, perturbative approaches do not work. For this reason, non-perturbative approaches have to be used for studying the properties of hadrons. Among several non-perturbative approaches, QCD sum rules is one of the reliable methods which is applied to understand the properties of hadrons and their interactions. In this thesis, the semileptonic rare decays of $B$ meson to $K_{1}(1270)$ and $K_{1} (1400)$ are analyzed in the framework of three point QCD sum rules approach. The $Brightarrow K_{1} (1270,1400) ell^+ ell^-$ decays are significant flavor changing neutral current (FCNC) decays of the $B$ meson, since FCNC processes are forbidden at tree level at SM. These decays are sensitive to the new physics beyond SM. The radiative $Brightarrow K_{1}(1270) gamma$ decay is observed experimentally. Although semileptonic $Bto K_1(1270,1400)$ decays are still not observed, they are expected to be observed at future B factories. These decays happens at the quark level with $brightarrow s ell^+ ell^- $ transition, providing new opportunities for calculating CKM matrix elements: $V_{tb}$ and $V_{ts}$. Applying three point QCD sum rules to $Brightarrow K_{1} (1270,1400) ell^+ ell^-$ decays is tricky, due to the fact that the $K_{1} (1270)$ and $K_{1} (1400)$ states are the mixtures of ideal $^{3}P_{1}(K_{1}^{A})$ and $^{1}P_{1}(K_{1}^{B})$ orbital angular momentum states. First, by taking axial vector and tensor current definitions for $K_1$ mesons, the transition form factors of $Brightarrow K_{1A} ell^+ ell^-$ and $Brightarrow K_{1B} ell^+ ell^-$ are calculated. Then using the definitions for $K_1$ mixing, the transition form factors of $Brightarrow K_{1} (1270,1400) ell^+ ell^-$ decays are obtained. The results of these form factors are used to estimate the branching ratio of $B$ meson into $K_1(1270)$ and $K_1(1400)$. The results obtained for form factors and branching fractions are also compared with the ones in the literature.

Neutrino-electron scatterings are purely leptonic processes with robust Standard Model (SM) predictions. Their measurements can therefore provide constraints to physics beyond SM. The &nu / e &minus / e&minus / data taken at the Kuo-Sheng Reactor Neutrino Laboratory were used to probe two sceneria: Non-Standard Neutrino Interactions (NSI) and Unparticle Physics. New constraints were placed to the NSI parameters (&epsilon / eL , &epsilon / eR ), (&epsilon / eL , &epsilon / eR ) and (&epsilon / eL , &epsilon / eR ) , as well as to the coupling constants for scalar (&lambda / 0 ) and vector (&lambda / 1 ) unparticles to the neutrinos and electrons.

The aim of the OPERA experiment is to verify the neutrino oscillation, directly measuring the appearance of from an initially pure beam produced at CERN. For this purpose OPERA detector is located underground Gran Sasso Laboratory(LNGS) 730 km away from CERN. The detector structure designed to be a hybrid system consisting of emulsion targets and electronic detectors. Total area of the emulsion targets in the OPERA detector is around 110000 m2 which needs fast and reliable automatic scanning systems. For this purpose, two dierent automatic scanning systems were developed in Japan and Europe. For now there are 12 scanning laboratories dedicated to the OPERA Experiment. The Emulsion Scanning Laboratory in the Physics department of METU is one of the scanning laboratories for the OPERA Experiment. The automatic scanning system in METU is European type which is using commercial hardware for easy construction and maintain. Also the laboratory has a unique feature in terms of experimental high energy physics laboratories. The emulsion scan- ning laboratory in METU is the

Forward Jet Calibration for CMS detector is presented using Z boson + jet event samples in the pseudorapidity region of 0 &lt / |&eta / | &lt / 5. The results are based on proton-proton collision data at center of mass energy of &radic / s = 7 TeV corresponding to &sim / 1 fb&minus / 1 of data. Z bosons are reconstructed from opposite sign lepton pairs (&mu / +&mu / &minus / , e+e&minus / ) and the transverse momentum balance of the Z boson and the associated jet is used to derive the calibration coefficients. The coefficients are tested on jets from a WW Monte Carlo sample using the W-mass constraint. The W mass peak position is observed to be improved by 20 % without loss of resolution.

Conventional Heavy Quarkonium systems, Charmonium and Bottomonium, are believed to be composed of a heavy quark and anti-quark pair. These systems are investigated by dierent methods resulting from dierent approaches to Quantum Chromodynamics (QCD), such as Lattice QCD, Eective Theories and Sum Rules. In this thesis we study the spectrum of Charmonium and Bottomonium using a non-relativistic Quark Model. Assuming one gluon exchange for the short distances and a linear confining potential for long distances we derive Breit-Fermi interaction Hamiltonian and calculate the spectra arising from this Hamiltonian. Also we calculate the partial widths of E1 and M1 radiative decays.