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

3.1 The Double Chooz detector 43
to its high thermal neutron cross section.
In order to reduce the systematic errors two identical detectors are employed.
A far detector, located around the first minimum of the ¯⌫ e disappearance
probability, measures the deficit in the ¯⌫ e flux. A near detector, placed as
closest as possible to the reactor core, measures the un-oscillated ¯⌫ e flux, in
order to get rid of the uncertainty on the knowledge of ¯⌫ e flux. Furthermore,
identical detectors at di↵erent distances allow to perform a relative measure
reducing the detector related uncertainties.
tel-00821629, version 1 - 11 May 2013
This chapter describe in full details the Double Chooz experiment (DC).
The detector design is described accurately in Sec. 3.1 highlighting the improvements
with respect to the previous CHOOZ experiment. The detector
read-out chain, from the photon electrons generated by the PMT to the
waveform digitised by the FADC is described in Sec. 3.2. The online system
which read, upon trigger, the FADC memories and write data events on disk
is described in Sec. 3.3. Sec. 3.4 briefly describes the systems dedicated to
the calibration of the detector response.
Sec. 3.5 discuss the simulation of the reactor ¯⌫ e flux, used to obtain the
expected neutrino energy spectrum to compare with the one measured by
the FD and infer the value of the mixing angle ✓ 13 . The detector Monte
Carlo model and the simulation of the read-out chain used to simulate the
detector response are described in Sec. 3.6 and 3.7.
Finally, the algorithms used to reconstruct important quantities such as the
deposited charge, the energy and the interaction vertex of each recorded
event are described in Sec. 3.8.
3.1 The Double Chooz detector
Two functional identical detectors located at di↵erent baselines from the
nuclear reactors are employed by DC for ¯⌫ e detection.
The FD is installed in the laboratory hall previously used by the CHOOZ
experiment [36], located at a mean distance of 1050 m from the reactor
cores, near the first oscillation minimum due to ✓ 13 . The detector has an
overburden of 300 m.w.e of rock, which reduce the muon trigger rate to
about 10 Hz in the inner detector volume. An average of about 36 ¯⌫ e /d
has been observed by the FD in the period considered in Ch. 4 with about
2.2 evt./d of background contamination.
The near detector (ND) will be placed at a mean distance of 400 m from
the reactor cores, where oscillation e↵ects due to ✓ 13 are expected to be
negligible. The ND will have an overburden of about 120 m.w.e. As a result
of the proximity of the ND to the reactors, a rate of 400 ¯⌫ e /d is expected
with a background contamination of about 11 evt./d [37].
The FD was build between 2009 and 2010 and is taking regular data since