Etudes des proprietes des neutrinos dans les contextes ...

tel-00450051, version 1 - 25 Jan 2010
The Sudbury National Observatroy (SNO) experiment
The Sudbury Neutrino Observatory (SNO) is a neutrino observatory located 6800
feet underground 6 in Vale Inco’s Creighton Mine in Sudbury, Ontario, Canada.
The detector was designed to detect solar neutrinos through their interactions
with a large tank of heavy water surrounded by approximately 9600 photomultiplier
tubes. Unlike previous detectors, using heavy water would make the detector
sensitive to three reactions. In addition to the reaction Eq.(2.3), SNO can detect
neutrinos through the charged-current reaction
νe + d → p + p + e − , (2.4)
where the neutrino energy should be at least Emin = 1.44 MeV and the neutral
current reaction
νx(νx) + d → νx(νx) + p + n (2.5)
which threshold is Emin = 2.23 MeV. The CC reaction (2.4) is very well suited for
measuring the solar neutrino spectrum. Unlike in the case of νae scattering (2.3)
in which the energy of incoming neutrino is shared between two light particles in
the final state, the final state of the reaction (2.4) contains only one light particle
– electron, and a heavy 2p system whose kinetic energy is very small. Therefore
by measuring the electron energy one can directly measure the spectrum of
the solar neutrinos. The cross section of the NC reaction (2.5) is the same for
neutrinos of all three flavours, and therefore oscillations between νe and νµ or ντ
would not change the NC detection rate in the SNO experiment. On the other
hand, these oscillations would deplete the solar νe flux, reducing the CC event
rate. Therefore the CC/NC ratio is a sensitive probe of neutrino flavour oscillations.
After extensive statistical analysis, it was found that about 35% of the
arriving solar neutrinos are electron-neutrinos, with the others being muon- or
tau-neutrinos. The total number of detected neutrinos agrees quite well with the
predictions from the SSM [4]. While the Superkamiokande result were not conclusive
about the solar neutrino problem, SNO brought the first direct evidence of
solar neutrino oscillation in 2001. The solar experiment are suitable to measure
a precise mixing angle, but the mass squared difference is better measured on
Earth, using electron anti-neutrino flux from nuclear reactors.
The Kamland experiment
The Kamioka Liquid Scintillator Antineutrino Detector (KamLAND) is an experiment
at the Kamioka Observatory, an underground neutrino observatory near
Toyama, Japan. It was built to detect electron anti-neutrino produced by the
nuclear powerplants that surround it, and to measure precisely the solar neutrino
6 The Creighton mine in Sudbury are among the deepest in the world and therefore present
a very low background radiation.
37