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

74 3. The Double Chooz experiment
tel-00821629, version 1 - 11 May 2013
as it goes through the bottom part of the IV. In addition, the muon is also
tagged by the large deposition in the ID due to the long track. A cut of
E ID = 30 MeV is set. This means that a sneaking muon is tagged via its
track-length in the scintillator ( x>15 cm for E = 30 MeV) or via its
Michel electron ( E>30 MeV, which covers ⇠ 50% of the Michel electron
energy spectrum).
Dedicated algorithms has been developed using the ID and the IV to reconstruct
the tracks of such muons. The ID algorithm relies on the Cherenkovlike
light cone emitted by the muons crossing the scintillator. The IV algorithm
is based on a log-likelihood minimisation using the photon arrival
time patterns determined from MC simulations. The spatial information
provided by the OV is also included in the track reconstruction.
The lateral resolution of the reconstructed track is determined at the detector
center, using MC simulations, to be about 35 cm for the ID and 60 cm
for the IV.
3.8.4 Energy reconstruction
The mixing parameter ✓ 13 is inferred by the comparison between the ¯⌫ e energy
spectrum obtained with the FD and the expected spectrum from MC
simulations. Uncorrected di↵erences between the energy spectra would affect
the measured of ✓ 13 . The energy reconstruction is thus an important
steps towards the comparison of energy spectra.
The energy scale is defined by the visible energy, E vis , measured in MeV
units, which provides the absolute calorimetric estimation of the energy deposited
per each trigger. The visible energy is obtained from the charge
reconstructed on each ID PMTs. The charge is converted into photo electrons
(PE) and multiplied by factors correcting for detector uniformity and
stability and finally converted in MeV:
E vis = PE m ⇥ f m uniformity ⇥ f m stability ⇥ f m MeV . (3.14)
where m refers to data or MC. The PE conversion is obtained from the sum
of the charge per channel as:
PE =⌃ i PE i =⌃ i q i ⇥ gain i (q i ) (3.15)
The gain i (qi) is extracted for each channel from the PE distribution obtained
during IDLI runs [18]. It corrects the non-linearity of the charge
reconstruction around the SPE charge equivalent, as shown in Fig. 3.24.
Such curve is measured per each power-cycle period and per channel.
The detector response is intrinsically non-uniform across the detector volume
due to several e↵ects of the optical model. Response map of the H-capture
gamma line is then used to characterise the response variations across the
full volume in the ID [88]. The response uniformity factor, f uniformity of