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

148 5. Correlated background
Upon Digital Q max /Q tot cut, such events disappear. The HELN rejection
e ciency (✏ HELN ) is estimated to be of 99.7 % by the fraction of events
rejected by the cut.
Prompt energy
Delayed energy
Entries
2
10
On Time coincidence
On Time coincidence + HE LN Cut
Entries/250keV
10
10
1
1
0 5 10 15 20 25 30
prompt E (MeV)
20 25 30 35 40 45 50 55 60 65
delayed E (MeV)
tel-00821629, version 1 - 11 May 2013
PMT prompt number PMT with Qmax the Qmax (Prompt)
Entries
45
40
35
30
25
20
15
10
5
0
0 50 100 150 200 250 300 350 400
PMTwithQmax
PMT number with the Qmax
PMT delayed number PMT with the Qmax Qmax (Delayed)
Entries
40
35
30
25
20
15
10
5
0
0 50 100 150 200 250 300 350 400
PMTwithQmax
PMT number with the Qmax
Figure 5.28: SM selection with (yellow) and without (withe) Digital
Q max /Q tot cut. SM events are expected below the detector chimney, so
the PMT with Q max is expected at the top of the detector (PMT number <
50). After the Digital Q max /Q tot cut a reduction of such events is observed
for the prompt event (bottom left), suggesting the rejection of some physics
events. Assuming the events depositing the maximum charge on the PMTs
whose number is < 50 are pure SM events, the physics selection e ciency
is estimated to be 61.7 ± 12.1 %.
Fig. 5.28 shows on-time selection with (yellow) and without (withe) Digital
Q max /Q tot cut. SM events are expected below the detector chimney, so the
PMT with Q max is expected at the top of the detector (PMT number <
50). After the Digital Q max /Q tot cut a reduction of such events is observed
in Fig. 5.28 (bottom left), suggesting the rejection of some physics events.
Assuming the events depositing the maximum charge on the PMTs whose
number is < 50 are pure SM events, the physics selection e ciency is estimated
to be 61.7 ± 12.1 %. The SM spectrum of Fig. 5.28 (top left) is then
fitted with a flat and a sloped linear models. The SM rate is computed in
agreement with Eq. 5.7, correcting for the Digital Q max /Q tot cut e ciency.
Results are shown in Fig. 5.29 and summarised in Tab. 5.15.