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

82 4. Measurement of ✓ 13 with the Double Chooz far detector
The ¯⌫ e searches are performed looking for time coincidence between a prompt
event, defined by the IBD positron energy loss in the scintillator and its following
annihilation, and a delayed event, defined by the delayed capture of
the IBD neutron on Gd.
The prompt events are selected by requiring their energy to be between
0.7 MeV and 12.2 MeV. The low energy bound is defined by the lowest postel-00821629,
version 1 - 11 May 2013
Figure 4.3: Fractional excess of IBD-like candidates with respect to the
expected ¯⌫ e , as a function of the time to the last tagged-muon ( T (µ)).
The coloured band represent 1 uncertainty. The increase of the fractional
excess of IBD-like candidate as we get closer it time to the last tagged-muon
indicate the existence of correlated background. A veto time of 1000 µs from
the last tagged-muon is applied to reject correlated background.
3.8.3). The fractional excess of IBD-like candidates with respect to the
expected ¯⌫ e , as we get closer in time to the last tagged-muon is shown in
Fig. 4.3 with 1 uncertainty, represented by the coloured band. The increase
of IBD-like candidates as T (µ) goes below 600 µs indicates the existence
of correlated events satisfying the ¯⌫ e selection as defined in Sec. 4.2. Accidental
backgrounds do not contribute to this estimation. For instance, at
T (µ) around 450 µs, there is 1 % increase in the correlated background
leaking into the ¯⌫ e sample. A veto time of 1000 µs is set since the increase
of correlated background is negligible (less than 0.2 % at 1 ) [89].
Fig. 4.4 shows the detector live time, defined as the run time once corrected
by the muon veto time, as function of the day [77]. The muon veto introduces
a dead time of 4.4 % with respect to the run time, the total live time
of 228.16 d is therefore the e↵ective time devoted to the search for neutrino
candidates.
4.2 ¯⌫ e signal selection