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

134 5. Correlated background
evt.
IVT 110
3
¯⌫ e +IV /n 19
IVT bkg. subtracted 89
Table 5.7: Summary of the number of IVT events, background events and
the total number of events upon background subtraction.
5.4.4 Fast Neutron shape and rate
tel-00821629, version 1 - 11 May 2013
The FN spectral shape S FN (E) is obtained by fitting the background subtracted
IVT spectrum shown in Fig. 5.18. Since the IVT spectrum appear
to be rather flat, a linear model is fitted. The total untagged FN rate (R FN )
is obtained by Eq. 5.6:
R FN =
⇢ t
⇥ 1 Z 12.2 MeV
⇥
✏ t ⇥ ✏ IV T t live 0.7 MeV S FN(E)dE (5.6)
where the IVT rate is corrected for the FN/SM separation e ciency (✏ t ) and
purity (⇢ t ) and scaled for the IVT e ciency (✏ IV T ), summarised in Tab. 5.8.
✏ IV T ✏ t ⇢ t t live [d]
0.33 ± 0.05 0.78 ± 0.01 0.97 ± 0.08 240.17
Table 5.8: Scaling factors to obtain the untagged amount of FN events and
total detector live time for rate computation.
Tab. 5.9 summarise the total statistical uncertainty, the uncertainty coming
from the backgrounds subtraction and the systematic uncertainties induced
by the scaling factors. The most important contribution to the total uncertainty
comes from the backgrounds subtraction, which is limited by the
low statistic of the background sample as summarised in Tab. 5.7. While
the uncertainty on the ¯⌫ e +IV /n background is expected to improve only
with a bigger data sample, the uncertainty on the background is expected
to improve by selecting the background with multiple o↵-time window, in
order to increase the statics of the sample. Systematic uncertainties are
propagated to the IVT spectrum bin by bin.
The linear fit to the IVT spectrum and its 1 uncertainty are shown in
Fig. 5.19 . Both a flat and a sloped linear model are tested and the results are