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

5.4 Fast Neutrons analysis 129
Prompt ID - IV Pulse DT
Entries/(8 ns)
50 Untag
Entries 7447
Mean 47.74
Untagged sample
RMS 64.69
2
/ ndf
257.4 / 35
C 8.743 !
0.552
IV Tagged sample
24.28 !
3.02
" 48.36 !
3.01
45
40
35
30
25
20
15
10
5
0
Tag
Entries 140
Mean 38.29
RMS 54.5
2
/ ndf
26.97 / 35
C 1.555 !
0.239
16.14 !
2.04
" 46.89 !
2.34
-50 0 50 100 150 200
TStart DT (ns)
tel-00821629, version 1 - 11 May 2013
Figure 5.15: Di↵erence between IV and ID pulse start time for untagged
(grey) and IVT (violet) sample. The pulse start time distribution shows a
correlated component within a rather narrow peak and a flat uncorrelated
component o↵-peak. The pulse start time distribution is fitted (black line)
with a constant function, to account for the uncorrelated component, and a
gaussian function, to account for the correlated one. The background contamination
is estimated integrating the flat component to be 58 ± 8events.
The background is then reduced by applying a cut in the pulse start time.
Requiring events on-peak, within [ 2, 95] ns (i.e., 3 ), allows to select
⇠ 99.7 % of the FNs while rejecting ⇠ 67 % of the background.
TStart DT (ns)
Prompt Tstart DT (IV - ID) vs E
200
150
100
50
0
-50
-100
0 5 10 15 20 25 30
Energy (MeV)
Figure 5.16: Di↵erence between IV and ID pulse start time as a function of
the prompt energy for untagged (grey) and IVT (violet) sample. The correlation
with energy suggests the events on-peak (energy up to 30 MeV) to
be most likely FN while the o↵-peak flat component (energy up to 12 MeV)
to be most likely ¯⌫ e +IV /n background.