The nature of the dark matter in the Universe is one of the greatest mysteries in modern astronomy. The neutralino is a nonbaryonic dark matter candidate in minimal supersymmetric extensions to the standard model of particle physics. If the dark matter halo of our galaxy is made up of neutralinos some would become gravitationally trapped inside massive bodies like the Earth. Their pair-wise annihilation produces neutrinos that can be detected by neutrino experiments looking in the direction of the centre of the Earth. The AMANDA neutrino telescope, currently the largest in the world, consists of an array of light detectors buried deep in the Antarctic glacier at the geographical South Pole. The extremely transparent ice acts as a Cherenkov medium for muons passing the array and using the timing information of detected photons it is possible to reconstruct the muon direction. A search has been performed for nearly vertically upgoing neutrino induced muons with AMANDA-B10 data taken over the three year period 1997-99. No excess above the atmospheric neutrino background expectation was found. Upper limits at the 90 % confidence level has been set on the annihilation rate of neutralinos at the centre of the Earth and on the muon flux induced by neutrinos created by the annihilation products.

<p>This thesis reports on searches for supersymmetric particles, in particular neutralinos, conducted with the DELPHI detector at the LEP accelerator at CERN. The searches were performed within the framework of the Minimal Supersymmetric Standard Model (MSSM), with<i> R</i>-parity conserved and gravity mediated supersymmetry breaking.</p><p>The neutralino search covered both <i>Χ</i>0₂<i>Χ</i>0₁ and<i> </i><i>Χ</i>0<i>jΧ</i>_i0<i>i</i> (<i>j </i>=3,4 and <i>i </i>=1,2) production channels. Data collected in 1999 and 2000 were used, in total about 451 pb^-1 at centre-of-mass energies from 192 to 208 GeV. No signal was found in any of the search channels, and the results were interpreted as model independent limits on the production cross-sections of the different topologies. For deriving these limits the data analysed here were combined with those collected at a centre-of-mass energy of 189 GeV (∾ 158 pb^-1). The obtained upper limits of the cross-section for ~<i>Χ</i>0₂<i>Χ</i>0₁ production, when <i>Χ</i>0₂→ <i>Z</i>*<i>Χ</i>0₁, vary with masses of the neutralinos involved and typically range between 0.05 pb and 0.8 pb.</p><p>The negative results from all sparticle searches were used to exclude regions in the parameter space within a constrained MSSM, with gaugino and sfermion mass unification at the GUT scale, and to set limits on the sparticle masses. The mass of the lightest neutralino is constrained to be larger than 45.5 GeV/<i>c</i>² for any <i>m</i>₀, for tan <i>β ≤ </i>40 and without sfermion mixing. An interpretation of the results was also performed within the Anomaly Mediated Supersymmetry Breaking model, and the lower mass limit of the lightest neutralino is 68 GeV/<i>c</i>². All limits are given at 95% confidence level.</p><p>In the ATLAS combined testbeam 2004, a full slice of the ATLAS detector was tested. The SPS accelerator at CERN was used to create particle beams with energies from 1 to 350 GeV. The beamline instrumentation, such as scintillators, beam chambers and Cherenkov detectors, and extra detectors, are described in this thesis. The data from the testbeam were used to investigate the performance of the hadronic calorimeter for pions at various pseudorapidities and energies. The energy resolutions and linearities obtained were found to be comparable with results from earlier hadronic standalone testbeams. The obtained resolutions were about σ/<i>E</i> = 52 % / sqrt <i>E </i>[<i>GeV</i>] ⊕ 5 %.</p>

<p>This Master  thesis considers certain aspects of Supersymmetric Quantum Mechanics in the context of Path integral approach. First we state all the basic mathematical structure involved, and carry out some basic Gaussian integrals for both commutative and non-commutative variables. Later in the thesis these simple results obtained are generalized to study the Supersymmetric sigma models on flat and curved space. And we will recover the beautiful relationship between the supersymmetric sigma  model and the geometry of the  target manifold in the form of topological invariants of the manifold, for the models on curved space.</p>

This thesis reports on searches for supersymmetric particles, in particular neutralinos, conducted with the DELPHI detector at the LEP accelerator at CERN. The searches were performed within the framework of the Minimal Supersymmetric Standard Model (MSSM), with R-parity conserved and gravity mediated supersymmetry breaking. The neutralino search covered both Χ02Χ01 and Χ0jΧi0i (j =3,4 and i =1,2) production channels. Data collected in 1999 and 2000 were used, in total about 451 pb-1 at centre-of-mass energies from 192 to 208 GeV. No signal was found in any of the search channels, and the results were interpreted as model independent limits on the production cross-sections of the different topologies. For deriving these limits the data analysed here were combined with those collected at a centre-of-mass energy of 189 GeV (∾ 158 pb-1). The obtained upper limits of the cross-section for ~Χ02Χ01 production, when Χ02→ Z*Χ01, vary with masses of the neutralinos involved and typically range between 0.05 pb and 0.8 pb. The negative results from all sparticle searches were used to exclude regions in the parameter space within a constrained MSSM, with gaugino and sfermion mass unification at the GUT scale, and to set limits on the sparticle masses. The mass of the lightest neutralino is constrained to be larger than 45.5 GeV/c2 for any m0, for tan β ≤ 40 and without sfermion mixing. An interpretation of the results was also performed within the Anomaly Mediated Supersymmetry Breaking model, and the lower mass limit of the lightest neutralino is 68 GeV/c2. All limits are given at 95% confidence level. In the ATLAS combined testbeam 2004, a full slice of the ATLAS detector was tested. The SPS accelerator at CERN was used to create particle beams with energies from 1 to 350 GeV. The beamline instrumentation, such as scintillators, beam chambers and Cherenkov detectors, and extra detectors, are described in this thesis. The data from the testbeam were used to investigate the performance of the hadronic calorimeter for pions at various pseudorapidities and energies. The energy resolutions and linearities obtained were found to be comparable with results from earlier hadronic standalone testbeams. The obtained resolutions were about σ/E = 52 % / sqrt E [GeV] ⊕ 5 %.

The production of η mesons in proton-proton collisions has been studied with the WASA detector using internal pellet targets in the CELSIUS storage ring at the The Svedberg Laboratory in Uppsala. Data were taken at two beam energies, 1360 MeV and 1445 MeV, corresponding to CM excess energies of 40 and 72 MeV, respectively. The η was detected via its 2γ decay in a near-4π electromagnetic calorimeter, whereas the protons were measured by a combination of straw chambers and plastic scintillator planes in the forward direction. The measurements were kinematically complete. The analysis yielded 69·103 events at 1360 MeV and 93·103 events at 1445 MeV, with a background contribution of less than 5%. Data were acceptance-corrected using a parametrization of a matrix element which includes all states up to two units of total angular momentum. The final state interaction between protons in the 1S0 state was included by a momentum-dependent enhancement factor in the relevant amplitudes. Angular distributions of the final state, invariant mass spectra and Dalitz plots are presented. The cos θη-distribution is found to be anisotropic with its maximum at 90° at both energies. From the parametrization it is inferred that this is due to interference between the Ss and Sd final states. A significant contribution from the Pp final state is also needed to describe data. / CELSIUS/WASA

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This Master  thesis considers certain aspects of Supersymmetric Quantum Mechanics in the context of Path integral approach. First we state all the basic mathematical structure involved, and carry out some basic Gaussian integrals for both commutative and non-commutative variables. Later in the thesis these simple results obtained are generalized to study the Supersymmetric sigma models on flat and curved space. And we will recover the beautiful relationship between the supersymmetric sigma  model and the geometry of the  target manifold in the form of topological invariants of the manifold, for the models on curved space.

<p>This thesis treats two different projects, both aiming at experimental tests at hadron colliders of some specific predictions of the Standard Model (SM) of particle physics and of its Minimal Supersymmetric extension (MSSM). The thesis is based on four papers.</p><p>Papers I-III study the discovery potential for a heavy charged Higgs boson of the ATLAS experiment at the Large Hadron Collider (LHC). Charged Higgs bosons are part of the Higgs sector in many extensions to the SM and their detection would be an unambiguous sign of new physics.</p><p>If the charged Higgs boson is heavier than the top quark, its dominant decay mode is into a top and a bottom quark. Searches in this decay channel at ATLAS are difficult mainly due to the large top-quark pair-production background. The possible gain obtained when requiring 4 b-tagged jets for the signal events is studied, but no significant improvement compared to an analysis requiring 3 b-tagged jets is found.</p><p>If the masses of supersymmetric particles are sufficiently small, heavy charged Higgs bosons can decay into a chargino-neutralino pair. We show that in this decay channel charged Higgs bosons can be detected, given a favourable choice of parameters governing the MSSM.</p><p>In a large-mass-splitting MSSM scenario, the charged Higgs decay into a W boson and a neutral Higgs can have a large branching fraction. We conclude, however, that charged Higgs searches in this decay channel are made difficult by a large, irreducible SM background.</p><p>Paper IV describes a measurement of the top-quark pair production cross-section performed with the DØ detector at the Tevatron collider. Signal events in the muon+jets decay channel are selected using topological event characteristics and a preliminary result of σ(ttbar)=3.8 +1.1-1.1(stat) +0.9-0.8(syst) +0.3-0.2(lumi) pb is obtained using an integrated luminosity of 363/pb.</p>

This thesis treats two different projects, both aiming at experimental tests at hadron colliders of some specific predictions of the Standard Model (SM) of particle physics and of its Minimal Supersymmetric extension (MSSM). The thesis is based on four papers. Papers I-III study the discovery potential for a heavy charged Higgs boson of the ATLAS experiment at the Large Hadron Collider (LHC). Charged Higgs bosons are part of the Higgs sector in many extensions to the SM and their detection would be an unambiguous sign of new physics. If the charged Higgs boson is heavier than the top quark, its dominant decay mode is into a top and a bottom quark. Searches in this decay channel at ATLAS are difficult mainly due to the large top-quark pair-production background. The possible gain obtained when requiring 4 b-tagged jets for the signal events is studied, but no significant improvement compared to an analysis requiring 3 b-tagged jets is found. If the masses of supersymmetric particles are sufficiently small, heavy charged Higgs bosons can decay into a chargino-neutralino pair. We show that in this decay channel charged Higgs bosons can be detected, given a favourable choice of parameters governing the MSSM. In a large-mass-splitting MSSM scenario, the charged Higgs decay into a W boson and a neutral Higgs can have a large branching fraction. We conclude, however, that charged Higgs searches in this decay channel are made difficult by a large, irreducible SM background. Paper IV describes a measurement of the top-quark pair production cross-section performed with the DØ detector at the Tevatron collider. Signal events in the muon+jets decay channel are selected using topological event characteristics and a preliminary result of σ(ttbar)=3.8 +1.1-1.1(stat) +0.9-0.8(syst) +0.3-0.2(lumi) pb is obtained using an integrated luminosity of 363/pb.

<p>This thesis presents two measurements of the top quark using 230 pb-1 of data taken with the D0 detector at the Tevatron accelerator. The first measurement determines the top pair production cross section at sqrt(s)=1.96 TeV in proton-antiproton collisions. In the standard model of particle physics the top quark decays almost exclusively into a W boson and a b quark. Candidate events are selected by requiring that at least one jet in the event is tagged with the secondary vertex algorithm. The measured top pair production cross section is:</p><p>8.6 +1.6-1.5 (stat. + syst.) +- 0.6 (lumi.) pb.</p><p>The second measurement uses the observed and predicted number of events with 0, 1 and 2 b-tagged jets to estimate the ratio R:</p><p>R = B(t->Wb) / B(t->Wq)</p><p>where q stands for any down-type quark. The measured value is</p><p>R = 1.03 +0.19-0.17 (stat. + syst.)</p><p>in good agreement with the standard model prediction of R=1. The result can be used to obtain a lower limit for R:</p><p>R > 0.61 (95% C.L.).</p>