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High Energy Physics


The aims of this project were to support the participation of the University of São Paulo s high energy physics group in two fermilab experiments, e761 and e781. The first of them was already completed by the time the project started and this part of the project was confined to data analysis and simulations. The main goal of e761 was the study of the radiative decays of hyperons , although a number of other important aspects of hyperon physics were also investigated, such as inclusive polarization, magnetic moments, spin precession through channelling, etc. The most important results from e761 were the confirmation beyond doubt of the large and negative asymmetry in the radiative decay of polarized sigmas, the measurement of the branching ratio of the cascade minus radiative decay, a new upper limit for the branching ratio of the omega minus radiative decay and the first observation of inclusive polarization for the anti-sigma plus. The focus of the project however was the second experiment, e781, a systematic study of charmed baryon physics, from production to decay and spectroscopy. Our contribution to this experiment was much more ambitious as now , in addition to contributing to the data taking, simulation and data analysis, we built a large piece of the spectrometer, consisting of drift chambers for the fast particle spectrometer, a system of vectorial type chambers, totaling 2,600 sense wires. E781 investigates the physics of charmed baryons producing them with a secondary 650 gev/c negative beam, mostly pions and sigmas, impinging on a set of 5 nuclear targets, followed by a sophisticated system of silicon vertex detectors, wire chambers, TRD s, calorimetry and a large rich, for particle identification. E781 is currently taking data and the first results should start appearing by the end of 1997. (AU)

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