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Mesure des observables de polarisation dans la photoproduction de mésons à Graal. Optimisation de la reconstruction de traces pour l'analyse des canaux à trois particules chargées.

Abstract : The Graal experiment is dedicated to the nucleon spectroscopy via the meson photo-production and in particular to the measurement of the polarisation observables, which gives clearer informations on the resonant contributions to the nucleon excited states. The apparatus is composed by a Compton beam with energy in the range 0.5-1.5 GeV produced by backscattering of an Argon laser on the 6 GeV electrons of the ESRF storage ring situated in Grenoble (France). The software of the track reconstruction of a detector composed by two cylindrical multiwire proportional chambers has been optimised for the measurement of reaction channels with three charged particles in the final state. The spatial resolution and the efficiency of this detector have been estimated and tested on eta and omega photo-production on the proton, where the meson decay into three pions. The beam asymmetry Sigma, obtained with linearly polarised photons, has been measured for the first time in the gamma+p->K+Lambda reaction from threshold up to 1.5 GeV photon energy in the laboratory system. This observable is expected to be more sensitive, with respect to the cross section, to particular resonant contributions. The comparison of the beam asymmetry with a new isobar model, extended to energies in the system of the centre of mass up to 2.5 GeV, has shown that this observable is more sensitive to the nucleonic than to the hyperonic resonances.
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https://tel.archives-ouvertes.fr/tel-00001357
Contributor : Luisa Nicoletti <>
Submitted on : Tuesday, May 21, 2002 - 1:02:41 PM
Last modification on : Thursday, November 19, 2020 - 12:58:41 PM
Long-term archiving on: : Friday, April 2, 2010 - 7:54:41 PM

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Luisa Nicoletti. Mesure des observables de polarisation dans la photoproduction de mésons à Graal. Optimisation de la reconstruction de traces pour l'analyse des canaux à trois particules chargées.. Physique Nucléaire Théorique [nucl-th]. Université Joseph-Fourier - Grenoble I, 2002. Français. ⟨tel-00001357⟩

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