| Summary: | In this thesis I describe \boom (Balloon Observation Of Microwave Extragalactic Radiation ANd Geophysics), a telescope mounted on a long duration stratospheric balloon, devoted to the measurement of extragalactic radiation in the microwave band of the electromagnetic spectrum. This work is not a complete description of the experiment, rather it is a presentation of a part of the research work done during my doctorate. A full description of the experiment and of the results obtained with it in the last years are given in the several referred articles and collaborators Ph.D. theses. \boom is an experiment of wide scientific interest, which gave in year 2000 a main contribution to cosmology, crossing for the first time what was considered a knowledge {\it frontier} in the field: to obtain a high signal to noise ratio maps of the cosmic background radiation. From those maps was possible to measure the value of the total energy density of the Universe, $\Omega_0 \simeq 1$, with important consequences on the description of our Universe. In this work I particularly treat the 2003 setup of \boomn, which flew in January of that year from Antarctica, measuring cosmic background temperature and polarization anisotropy. In the cosmic microwave background a level of linear polarization of the order of 1-5\% of the temperature anisotropy intensity is expected. The angular power spectrum of that polarized signal should be characterized by features strictly linked to the cosmological model. Observation of the angular power spectrum of polarization can confirm the model and improve the precision in the measurement of the cosmological parameters, the numbers that quantitatively describe the evolution of the Universe. The work is experiment-oriented because such was my research work, even if space is given to description of data analysis tasks. In Chapter~\ref{chap:cmb} I introduce the cosmic background radiation science, particularly focusing on information obtainable from polarization measurements and on the relevant physical ...
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