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The ATLAS (A Toroidal LHC ApparatuS) detector is one of the four detectors which will be installed in the new accelerator, at LHC, CERN. One of the experiments' research aims is the discovery of the Higgs particle and thus, the confirmation or not of the Standard Model. The Muon Spectrometer of the detector has special importance, because the decay channels of the Higgs particle which have muons at the final state are clear signatures of the existence of the Higgs particle. This project focuses on the Higgs decay through the channel: H->ZZ->4mu. The alignment of the muon detectors has to be very accurate, so that its contribution on the measurement of the muons' momentum, to be low compared to the intrinsic resolution of the detectors themselves. Although the alignment of the muons detectors at the barrel and the end-caps regions is well controlled, the relative alignment of the end-caps with respect to barrel is not controlled with the same accuracy. In this project, we study the influence of such misalignments (translations and rotations) on the search of the Higgs particle (width and discovery potential), which decays through the channel mentioned above. The first part of the project refers to the Physics of the ATLAS detector, to its specific construction features and finally to the alignment scheme of the muon detectors at the barrel and forward region. In the second part, there is a detailed reference to the data acquisition and analysis, using the muon spectrometer alone. The method, the mathematical formulation and the C++ programming application concerning the fitting of the muons' tracks under the constraint of the parent's Z invariant mass (Constraint Fitting) are presented. This method results in diminishing the reconstructed Higgs width,therefore in improvement of the Signal/Background ratio. Finally, the applied misalignments (translations and rotations) of the one end-cap with respect to the barrel are presented and the effects on the determination of the mass and the width of the Higgs and Z particles are studied. At the conclusions, we mention the usage of the well-known Z width in order to isolate the kind and the amount of the probable misalignments.

Fig. 6, Fig14, Fig15, Fig16, Fig17, Fig18

The project refers to the participation of the Department of Physics (at the Aristotle University of Thessaloniki) at the construction of the Muon Spectrometer for the ATLAS Experiment (LHC - CERN). I begin with a brief introduction concerning the drift chambers and their principles, allowing the detection and, therefore the study, of the particles' tracks. I describe in details the setup for data acquisition (hodoscope and electronics) and I produce the delay curve for the hodoscope, thus providing the triggering. The time spectrum of a Monitored Drift Tube (MDT) is given. Finally, I present the software (developed using the LabView software tool) used for the track reconstruction, from the cosmic-rays hits given by the 4x4 MDT chamber.

Initially, there is a review of the already known terms (from the classical, hamiltonian mechanics) of the canonical phase space and the Liouville's theorem. The definition of the beam emittance of accelerating particles is then given. I also deal with the phase portraits, as a way for the geometrical description of the motion. Finally, I conclude with the establishment of the emittance using this time the statistical method.

In this report, a detailed calculation of the differential cross section for the photoelectric effect is carried out (Fermi's Golden Rule, matrix element, interaction hamiltonian....). I comment on the result and I plot the angular distribution of that differential cross section. In addition, I compare the total cross sections for several processes, as a function of the energy. Finally, a detailed reference to the mass absorption coefficient is done.

Histograms : 3a 3b 4 5a 5b 6a 6b 7a 7b 8 9 10 11 12 13 14 17a 17b 18

During this project, I study the reconstruction of 2-dimensional tracks of charged particles moving through a vertical and homogeneous magnetic field. The study is done with Monte Carlo track generation. I study how several parameters (magnetic field, momentum, etc) could affect the efficiency of the reconstruction, while I calculate the residuals for each detector layer's. Finally, I approach the parameters of a real-life experiment and I discuss further developments that can be done.

Initially,there is a detailed reference of the time spectra and of the topology of a gamma-ray burst (GRB). I refer to the optical emission of a GRB and I develop the several models ( thermonuclear model, pulsars etc ) that are used to describe the GRB's. At the end, the event GRB990123 (time spectrum, light curve etc) is described as a characteristic example of such a burst.

The report refers to the basic ideas of the EUSO (Extreme Universe Space Observatory). I mention the physical processes that the detector is going to study ( Čerenkov and fluorescence radiation) and how this is going to be implemented. Furthermore, I refer to the specific parts of the detector (main telescope, optical lenses, filters, focal surface), analyzing the working principles of them. Finally, the EUSO observing efficiency (duty cycle, expected EUSO performance, comparison with ground based observations) is discussed in detail.