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Neutrinos as a Probe to Physics beyond the standard model of particle Physics

Final Activity Report Summary - NUOSC (Neutrinos as a Probe to Physics beyond the Standard Model of Particle Physics)

Dr Sorel contributed to complete our understanding of neutrinos, the least understood fundamental matter particles known, via experimentally addressing the several questions raised by the discovery of neutrino flavour oscillations over the last decade.

Evidence for neutrino flavour change among the three neutrino types participating in weak interactions, namely electron, muon and tau neutrinos, was established beyond any doubts. The body of evidence, originating from neutrinos produced in the Sun, in cosmic ray interactions in the Earth's atmosphere, in nuclear reactors and in man-made particle accelerator beams, fit beautifully within the framework of three flavour neutrino oscillations occurring during neutrino propagation. This, in turn, implied that neutrinos are massive particles and that mixing among neutrino weak and mass states occurs, providing the first and, so far, only direct evidence for physics beyond the standard model of particle physics.

These implications might have profound and far-reaching consequences, as they could constitute a window to our understanding of fundamental physics at a high energy scale, where a more general and unifying description of matter than the one provided by the standard model might hold. In addition, it became clear that a more accurate knowledge of neutrino properties constituted an essential ingredient for our understanding of how the Universe has evolved, given that in nature neutrinos are only outnumbered by photons.

Among his research activities at the host institution, Dr Sorel played a leading role in the analysis of forward pion production in proton-nucleus interactions with the Hadron production (HARP) experiment at the European Organisation for Nuclear Research (CERN), as well as on the application of those results for neutrino flux predictions for the K2K experiment in Japan and for the MiniBooNE and SciBooNE experiments at Fermilab, in the United States of America. This contribution was of critical importance for the final K2K neutrino oscillation measurements and searches, providing the first confirmation of atmospheric neutrino oscillations with a long baseline accelerator experiment. It was also critical for the first MiniBooNE results on a search for electron neutrino appearance, excluding the simplest neutrino oscillation interpretation of the electron antineutrino excess seen in the earlier Liquid scintillator neutrino detector (LSND) experiment.

Dr Sorel also got heavily involved in the experimental study of all relevant neutrino interactions in the few GeV neutrino energy region and was coordinating, since January 2006, together with Dr F. Sanchez from the Institut de Fisica d'Altes Energies (IFAE), Barcelona, Spain, the activity of the analysis group making use of the SciBar detector, one of the neutrino detectors exposed to the K2K neutrino beam and located at the KEK Laboratory in Japan. In addition, Dr Sorel was one of the leaders of the SciBooNE experiment at Fermilab, United States of America, whose main goal was to provide the precision neutrino interaction data needed for more sensitive neutrino oscillation searches and measurements to be performed with the future T2K experiment. The T2K experiment in Japan would occupy a prime role, within the world context, for the experimental exploration of neutrino properties over the next decade. Dr Sorel served as the software coordinator for the SciBooNE experiment since early 2006, and as the physics' analysis coordinator, along with Dr. H Tanaka, from Columbia University, United States of America, since early 2007.