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Mesure précise de la polarisation du faisceau d'électrons à TJNAF par polarimétrie Compton pour les expériences G^p _E et N-\Delta

Abstract : This work deals with electron beam polarization measurements using Compton effect at T JNAF, for experiments of the proton electromagnetic form factors measurement and for nucleon response functions determination in the pion electroproduction reaction near the ~(1232) region. The Compton polarimeter, whose principle is built on elastic electron-photon scattering, was designed and built around a high finess Fabry-Perot cavity (finess=25000). The incident Nd:YAG laser power is amplified by an optical cavity which provides a luminosity such as the statistical uncertainty on the electron polarization measurement is at the level of 1% in one hour. U sing Pound- Drever method, laser freq uency is locked on one of interferometer resonance frequencies. Circularly photon polarization inside the optical cavity was measured to be 99.6+/-0.45%. The electron beam polarization is deduced from the measurements of the photon polarization, experimental asymmetry and analysing power of our detector. The analysing power is determined by a measurement of the response function of the photon detector, composed of 25 PbW04 crystals, thanks to coincidence events detected with the electron detector made up of 4 plans of 48 silicon strips. Measurement uncertainties corne meanly from detector's response function modelling, pile up effect and photon beam polarization. Total relative uncertainty on the electron beam polarization measurement is about 1.4% for 40 minutes data taking. Moreover, the Compton polarimeter allows to estimate the electron helicity difference between two polarization reversaIs. This effect was found compatible with zero at 0.3%.
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Submitted on : Thursday, July 21, 2005 - 3:18:39 PM
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Stéphanie Escoffier. Mesure précise de la polarisation du faisceau d'électrons à TJNAF par polarimétrie Compton pour les expériences G^p _E et N-\Delta. Physique Atomique [physics.atom-ph]. Université Paris-Diderot - Paris VII, 2001. Français. ⟨tel-00009775v2⟩

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