Etude de bruit de fond induit par les muons dans l'expérience ...

tel-00724955, version 1 - 23 Aug 2012
3.1 Bolometers 61
(F)ID stands for (Fiducial) Interdigitised detector, with a numbering less than 100
for a mass of 320 g, greater than 200 for a mass of 200 g, and greater than 400 for
a mass of 400 g, cf. Section 3.1.4.
In EDELWEISS-II, there are too many bolometers to be handled by only one
computer. Thus, bolometers are combined in group of up to 10 per acquisition computer.
Each computer has its proper and independent DAQ. When one channel of a
detector of a DAQ computer triggers, the data of the bolometers on this computer
are registered independently from what happens in the DAQ of other computers.
There are as many runs as DAQ computers.
But note that a run is not a Run. In the data acquisition language, a measuring
period over a few weeks/months is called a Run. A Run is made up from typically
day-long runs intersected by regeneration periods of ∼ 1 h. In between two physics
Runs are generally a Research and Development (R&D) Run to install and test
more bolometers and improve the setup. Therefore the numbering of Runs is odd
for R&D Runs and even for physics data Runs.
The configuration of bolometers during the physics Run 8, 10 and 12 are shown
in Figure 3.5, 3.6 and 3.7, respectively. There are exclusively standard bolometers
during Run 8, except for one ID, which was implemented for test purpose. Run 8
reproduced EDELWEISS-I on a larger scale. The number of bolometers is growing
in between Run 8 and Run 10, with the installation of NbSi and ID bolometers.
However, there are less bolometers during Run 12, as the system switched to almost
exclusively high performing ID bolometers. During Run 12, as they are well known,
the standard bolometers are in as reference bolometer to witness the system behavior
and test the new electronics.
3.1.7 Data acquisition
For each detector, the data acquisition (DAQ) has to generate from 3 up to 7 channels
per bolometer: heat, ionization from the center electrode and ionization from
the guard electrode in the case of a standard Germanium bolometer; ionization from
the collecting electrode of a side, ionization from the veto electrode of the same side,
these two but for the other side, and the same again which correspond to the guard
and finally heat in the case of an interdigitised bolometer. The DAQ of EDELWEISS
is described in detail in [149, 160].
Basically when one channel of one detector triggers, all the other channels of all
detectors are registered and read out as one event. The ionization signal is saved
in a time window of 10 ms, the heat signal over 1 s. Besides the physics signal, the
baseline before the event is also registered, which is called the pre-trigger. The main
action is to choose between an ionization or a heat trigger.
The risetime of the ionization signals is ∼ 1000 times faster than the one for
the heat signals. The advantage is that the time of an event can be known very
accurately, and the search for the heat signal is then facilitated. However, the data
considered in this work have a heat trigger because of the following reasons:
• The baseline resolutions of the heat channel are typically twice as good as
those of the ionization channel.
• The ionization signal of a nuclear recoil event in Germanium is 3 times lower
than the one of an electronic recoil with the same energy deposit, while the
heat signals have the same amplitude. Therefore the trigger is more efficient
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