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

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• The SM analysis could be improved by reducing the energy window
used to select the delayed events. The contamination of high energy
light noise found in the SM selection is, as shown in Fig. 5.21, dominant
at high energy, > 40 MeV. A smaller energy window, i.e [20, 40] MeV,
is expected to provide a purer SM sample.
• More statistics in the future would help to clarify if the linear model
adopted for the correlated background shape is the correct one or if a
di↵erent model is required.
• In a similar way the OV veto reduce the correlated background, the
IV tagging could be employed to further reduce FN contamination. A
reduction of ⇠ 33 %, corresponding to the measured tagging e ciency,
is expected.
tel-00821629, version 1 - 11 May 2013
• The upper OV layer has been installed recently. It is expected to
tag muons with small zenith angles, capable to enter in the detector
through the chimney. In the future, the OV veto is then expected to
further reduce the SM background.
• The OV capabilities to tag the correlated background measured at high
energy, > 12 MeV, is observed to decrease at low energy, < 12 MeV,
causing a background reduction smaller then expected. The upper OV
layer could now be used to study the tagging e ciency as a function
of the energy < 12 MeV and the observed background reduction could
be validated.
• Once the data taking with both detectors will start, more detailed
studies will be possible. Since the near detector will be installed at
a smaller depth with respect to the far detector, an higher correlated
background rate is expected. The measurements performed with the
near detector could then be extrapolated to the far detector in order
to increase the accuracy of the correlated background estimation.
For the first time, this analysis allow to directly measure the correlated background
in the low energy region, where ¯⌫ e are observed. Past and present
experiments [36, 33, 31], measure the correlated background by extrapolating
the high energy tail of the prompt spectrum at low energy. A bias
could be introduced by extrapolating the high energy tail, since the shape of
the low energy part of the correlated background spectrum is expected to be
dominated by scintillator quenching and acceptance e↵ects, which introduce
a slope in the correlated background shape. Such a bias is expected to be
detector dependent. In this thesis, such method has been found compatible
with the results obtained by selecting the background at low energy, but a
bias of ⇠ 25 % has been found.