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

90 4. Measurement of ✓ 13 with the Double Chooz far detector
number of entries [per 20ms]
45
40
35
30
25
20
15
10
5
0
Entries 16975
2
! / ndf
1173.6 / 988
Li-9 rate 1.2203 ±
0.1287
constant 15.557 ±
0.128
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
"t [ms]
tel-00821629, version 1 - 11 May 2013
Figure 1: t-fit for the Li-reduced analysis (E µ > 600 MeV). Data points with error bars are
shown in black, the fit result as a solid red line.
Figure 4.12: Time correlation between ¯⌫ e -like candidates and suitable parent
muon, for E µ > 600 MeV. The distribution is fit with an exponential
and a flat component. The exponential component allow to estimate the 9 Li
rate produced by high energy muon to be (0.95 ± 0.11) cpd
cumulative number of events [normalized]
1
0.8
0.6
while the rate for events far from the muon track is extrapolated based on
the lateral distance profile
0.4
between muon and 9 Li candidate observed for
high energy muons. A0.2rate of 1.08 ± 0.36(stat) ± 0.25(syst) cpd is obtained.
Lithium
Lastly, the 9 Li rate produced by low energy muons neutrons (E< 275 MeV, muons
0
0 0.5 1 1.5 2 2.5 3
crossing the bu↵er and fraction of thelateral gamma-catcher) distance from muon track [m] is estimated from the
fit of the t distribution and it is found compatible with zero. An upper
Figure 2: LDP of 9 Li and cosmic neutron capture events with respect to parent HE muon tracks
limit of < 0.3
(E µ
cpd is established by the fit of the t distribution for events
> 600 MeV). Data points are obtained by fitting (Li) or counting (n) all events within a
near the muon given distance track cut from (d the < track, 0.8 m). and normalizing to the rate at 5 m (not shown). While there
are some di↵erences visible for short distances (d 600 MeV shower into the detector, they are
been found as the most likely the parents of 9 Li isotopes. For this reason the
0.5 ms veto is applied to the ¯⌫ e selection, after a showering muon of energy
above 600 MeV. The definition of parent muon and the veto condition were
varied to obtain the maximum veto e ciency for a fixed dead exposures of
⇠5 %.Thereduced 9 Li background rate is 1.25 ± 0.54 cpd [98].
Fig. 4.13 shows the 9 Li spectrum, obtained by selecting a purer sample of
9 Li events subtracting the ¯⌫ e background through o↵-time selection. The
obtained spectrum is then compared with MC simulation of the possible 9 Li
decay branches [56]. The
2 test performed between data and MC spectra