Etude et impact du bruit de fond corrélé pour la mesure de l'angle ...

2.4 Measuring neutrino oscillation parameters 27
The neutrino energy is of the order of few MeV and the average distance
between detector and reactors is of about 200 km. Given the mass squared
di↵erence measured by solar experiments of ⇠ 7.5⇥10 5 eV 2 , the oscillation
phase m 2 12L/(4E) is of the order of 1, which provide the best condition
for a precise measurement of the oscillation parameters.
The ¯⌫ e detection is performed through charged current inverse beta decay
reaction ⌫ e + p ! e + + n in liquid scintillator. The positron and the delayed
neutron capture on H gives a clean signature of ¯⌫ e interaction. The ¯⌫ e energy
is directly measured from the positron energy, E ⌫e = E e + + m n m p , giving
the possibility to measure the neutrino oscillation probability as a function
of the energy.
A precise determination of m 2 12 and the shape of the oscillation pattern
are obtained as shown in Fig. 2.5.
tel-00821629, version 1 - 11 May 2013
Figure 2.5: Ratio of the background and geo-neutrino subtracted antineutrino
spectrum to the expectation for no-oscillation as a function of L/E.
L is the e↵ective baseline taken as a flux-weighted average (L=180km) [16].
2.4.2 Experimental determination of m 2 23 and ✓ 23
The first measurement of m 2 23 and ✓ 23 has been performed by SK using atmospheric
neutrinos. Further measurements have been performed to confirm
SK results by K2K, MINOS and Opera using ⌫ µ produced at accelerators.
Results from global analysis are shown in Fig. 2.6 [91] and described in more
details in the following sections.
Atmospheric neutrinos
Atmospheric neutrinos are produced by cosmic rays interacting in the high
atmosphere producing mainly pions and kaons. The charged pions mainly