Thomas ROGER, Katholieke Universiteit Leuven, Belgique
Vendredi 11 Mars 2011 à 11h00 - Salle des Séminaires
scillation parameters from the solar neutrino spectrum observed on Earth.
Several experiments aiming at determining this intrinsic spectrum have been performed using different techniques. The latest results of Bhattacharya et al.  and Winter et al.  show large disagreement with the measurement of Ortiz et al. .
We have measured with a high precision the 8B beta final state distribution, reducing the systematic uncertainties. For this purpose, a 18.7 MeV 8B beam from the TRIµP separator at KVI was implanted in a 75 μm thick double-sided stripped silicon detector [4,5]. The detection of the two-alpha particles resulting from the decay of the three first 2+ states in 8Be, together with a full beta-summing GEANT4 simulation, enabled us to reconstruct the final state distribution with a precision of about 5 keV down to 400 keV excitation energy.
The R-matrix fit of this distribution will be presented, and the formalism used to describe the 8Be 2+ states sequence will be discussed.
By extracting the information directly from the two-alpha spectrum, we obtained a new reference for the undisturbed neutrino distribution, with errors reduced by a factor more than two.
 M. Bhattacharya et al., Phys. Rev. C73, 055802 (2006)
 W.T. Winter et al., Phys. Rev. Lett. 91, 252501 (2003)
 C.E. Ortiz et al., Phys. Rev. Lett. 85, 2909 (2000)
 D. Smirnov et al., Nucl. Instr. and Meth. A547, 480 (2005)
 J. Büscher et al., Nucl. Instr. and Meth. B266, 4652 (2008)
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