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

120 5. Correlated background
tel-00821629, version 1 - 11 May 2013
Figure 5.8: The IV energy spectrum obtained for di↵erent multiplicity condition.
Requiring the PMT multiplicity to be bigger than 2 rejects most of
the low energy events (< 0.25 MeV), likely due to PMT radioactivity, while
allows to tag physics events from very low energy (> 1.00 MeV).
most of the low energy events, < 0.25 MeV, and allows to tag physics events
with energy > 1.00 MeV. Fig. 5.9 show the vertex distribution of the IVT
sample. As expected for FN events, no correlations are observed for both
prompt and delayed events. Fig. 5.10 shows there is no correlation between
the ID and the IV energy depositions. Since the IVT rely on the high
multiplicity the FNs are created by their parent muon, the tagged FN is a
separated event from the one interacting in the ID.
Num. PMT hit evt. [0.5;30] MeV evt. [12;30] MeV ✏ IV T [%]
0 7447 199
2 156 65 33 ± 5
4 110 50 25 ± 4
6 94 45 23 ± 4
Table 5.2: Number of IVT events and tagging e
PMT multiplicity.
ciency (✏ IV T ), for di↵erent
Tab. 5.2 summarise the number of events passing IVT, between [0.5, 30] MeV
and [12, 30] MeV, where a pure sample of FN is obtained. The ratio of events
in [12, 30] MeV between the events passing the IVT over the total, give an