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

5.5 Stopping Muon analysis 145
Source stat. s H/L ✏ t ⇢ t total
[%] [%] [%] [%] [%]
Uncertainty 15.1 40 17.2 7.9 46.8
Table 5.13: Break down of statistical and systematic uncertainties.
tel-00821629, version 1 - 11 May 2013
induced by the scaling factors. The systematic uncertainties are propagated
to the SM spectrum bin by bin.
The linear fit to the tagged spectrum and its 1 uncertainty are shown in
Fig. 5.25. Both flat and sloped linear model are tested and the results are
summarised in Tab. 5.14. The flat linear model gives a
2 /ndf =7.1/8 and
a fit probability of ⇠ 52 %. Assuming the fitted flat spectrum, a SM rate of
(0.67±0.10) cpd is obtained. The sloped linear model gives a 2 /ndf =6.9/7
and a fit probability of ⇠ 44 %. Assuming the fitted sloped spectrum, a SM
rate of (0.62 ± 0.20) cpd is obtained. Both models shown compatible results
however the more generic sloped shape is used as spectral shape for SM
background, since there is no physical reason for a flat SM spectrum.
Fit const. slope 2 /dof R SM (R SM )/R SM
model [1/(3 MeV)] [1/(3 MeV) 2 ] [cpd] [%]
Flat 55.8 ± 8.9 – 7.1/8 0.67 ± 0.10 16
Slope 48.8 ± 24.0 0.4 ± 1.3 6.9/7 0.62 ± 0.20 32
Table 5.14: Summary of SM spectra parameters and SM background rate
for the flat and the sloped linear model.
5.5.3 Validating high energy light noise rejection
As discussed in the previous section, the LN rejection cuts applied for the
¯⌫ e searches are not enough to reject e ciently the HELN a↵ecting the SM
searches. In [44], the so called Digital Q max /Q tot , defined as the Q max divided
by the number of ID PMT hits, has been proposed as new variable for
HELN reduction. Such cut is considered and even optimised in this section
to validate the LN reduction method described in 5.5.1.
Fig. 5.26 shows distributions of Digital Q max /Q tot vs prompt and delayed
energy for HELN events and SM candidates. Delayed events are clearly distributed
above Digital Q max /Q tot of about 40 while prompt events appear