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

4.4 Selection e ciencies and systematics 93
A further independent measurement of the background is performed by
analysing 22.5 h of reactor o↵-o↵ data. The expected ¯⌫ e signal is < 0.3 %
events while 3 IBD-like candidate are observed. Two events have the prompt
energy of 4.8 MeV and 9.4 MeV and are associated within 30 cm and 240 ms
to the closest energetic muon, and are thus likely associated with cosmogenic
background. The third candidate has a prompt energy of 0.8 MeV and a
spatial distance of 3.5 m from the associated delayed event and is therefore
likely to be an accidental coincidence.
About 7 days of reactor o↵-o↵ data, taken immediately after the dataset
used in this work, are currently being analysed and will be the subject of a
dedicated paper.
4.4 Selection e ciencies and systematics
tel-00821629, version 1 - 11 May 2013
Since the current phase of the experiment involve the FD only, the e ciencies
related to the data selection are naturally taken into account comparing data
with MC expectation, performing an identical selection on the MC. Important
quantities are the remaining discrepancies between data and MC that
need to be assumed as systematic uncertainties. In the following sections
a description of the relevant selection e ciency and related systematics is
provided. The values are summarised in Tab. 4.2.
4.4.1 Trigger e ciency
The trigger e ciency is evaluated analysing the FEE stretcher pulse amplitude
(Sec. 3.2.2) at the trigger release time for events triggered independently
by pre-scaled trigger [92]. The stretcher pulse amplitude is then
converted into energy using the correlation map shown in Fig. 4.15.
The trigger e ciency curve obtained with this method is shown is Fig. 4.16.
Uncertainty on the trigger e ciency comes mainly from statistical fluctuation,
definition of trigger release time, energy conversion and from the
method itself. Systematics uncertainty due to the method has been taken
into account evaluating the discrepancies on the trigger e ciency obtained
with events triggered independently by the IV and by the two trigger boards
separately. The breakdown of systematic uncertainty is shown if Fig. 4.17.
The trigger e ciency is of about 50 % at 0.4 MeV and 100.0 0.0
0.1 % at 0.7 MeV
(prompt lower cut). Above 0.8 MeV the trigger e ciency is 100.0 ± 0.0 %
[93].
4.4.2 Neutron detection e ciency
The most significant source of ine ciency is the one related to the neutrino
detection, i.e. the delayed events. The e ciency related to the identification