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

26 2. Neutrino physics
tel-00821629, version 1 - 11 May 2013
The so called solar neutrino anomaly was finally solved by the SNO experiment
[30] using an heavy water (D 2 O) Cherenkov detector, sensible to
neutrino interactions through three di↵erent processes.
Elastic scattering, ⌫ x + e ! ⌫ x + e with x = e, µ, ⌧, involve all types of
neutrinos but with a di↵erent cross-section for ⌫ µ and ⌫ ⌧ . Naming x the
neutrino flux for the flavour x, elastic scattering allow to determine the flux
e +0.155( µ + ⌧ ). The charged current interaction, D + ⌫ e ! 2p + e,
only involve electron neutrino and therefore determines e. Finally the neutral
current interaction, D + ⌫ e ! p + n + ⌫ e , involves all neutrino flavour
with the same cross-section and allow to determine the total neutrino flux,
tot = e +( µ + ⌧ ).
The three di↵erent reactions measured three independent linear combination
of electron, muon and tau neutrino fluxes, as shown in Fig. 2.4. Such
measurement allowed to obtain clear evidence of solar neutrino oscillation
in term of ⌫ e ! ⌫ e,µ,⌧ , of which ⌫ e is only one third of the total. Moreover,
the total initial ⌫ e flux has been determined independently from theoretical
DETERMINATION OF THE ν
model.
e AND . . . . I DATA SET
8
SNO
SNO
φ
7 ES
φ CC
160
Data -(a)
BG - Geo ! e
Expectation based on
1
140 determined by
6
5
0.8
120
SNO
4
φ 100
NC
0.6
3
φ SSM
80
2
0.4 60
CC
1
40
0.2
0
20 NC + bkgd
0 1 2 3 4 5 6
6 -2 -1
φ e (10 cm s )
0 0
20 30 -1.0 40 50 -0.5 6
L
FIG. 41. (Color) Flux of 8 0
/E
!e
(
Figure 2.4: Solar neutrino fluxes determined
Bsolarneutrinosthatareµ
by SNO through
or τ flavor
elastic scattering
(ES) neutral current (NC) and(a)
charged current (CC) interactions.
(b)
500
vs flux of electron neutrinos deduced from the three neutrino reactions
(b)
in SNO. The diagonal bands show the total 8 Bfluxaspredictedby
The expected flux from the SSM is also shown and it is in agreement with
the BP2000 SSM [78](dashedlines)andthatmeasuredwiththeNC
400
the measured Fig.
reaction
total 7: Determination
in SNO
flux
(solid
[30]. of the electron and muon/tau neutrino fluxes by SNO (a). Elec
band). The intercepts of these bands with
the probability axes represent at KamLAND the ±1σ errors. (b). The bands intersect at the fit
300
values for φ e and φ µτ , indicating that the combined flux results are
consistent with neutrino flavor transformation with no distortion in
the 8 Bneutrinoenergyspectrum.
200
Long baseline the electron reactor andneutrinos
the delayed coincidence with the signal from the neutron ca
The neutrino energy is directly related to the positron energy, E
100 ⌫e = E
CC e +
The Kamioka Liquid-scintillator Anti-Neutrino Detector (KamLAND) experimentinmeasure
also interpreting played thean neutrino these important results. oscillation role Although in the probability the determination signal-extraction as a function of the solar of the energy and as a
+ m n
NC + bk
oscillation fit aparameters has goodthreem free 2 parameters, one should not subtract three
ES
12
[16]. determination [40] and ii) to observe the oscillation
degrees of freedom for each χ 2 0 pattern, inclu
KamLAND in the detected survival ¯⌫ e emitted probability, by several as ,sincethefitisaglobalfitto
shown nuclear Fig. power 7b[40]. plant Japan. 0.0 0.2 0
all three distributions. Furthermore, the actual signal extraction
is a fit to the three-dimensional data distribution, whereas the
χ 2 sarecalculatedwiththemarginaldistributions.These“χ 2 600
4.4 unknown oscillation parameters ”
(c)
values demonstrate that the weighted sum of the signal pdfs
The mixing angle ✓
500
provides a good match 13 has not been measured yet, but both direct and indirect bou
to the marginal energy, radial, and
angular from the distributions. CHOOZ and Minos experiments, mentioned above, and from the an
400
fects Figure in the 42 shows atmospheric the marginal and radial, solar neutrino angular, and experiments. energy The result of a global
distributions Fig. 8a [23]. of the data along with Monte Carlo predictions
300
for CC, ES and NC + background neutron events, scaled by
CC
s -1 )
cm -2
6
(10
φ µτ
Survival Probability
Events per 0.05 wide bin
Events per 0.1 wide bin
ts per 500 keV
PHY