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

tel-00724955, version 1 - 23 Aug 2012
3
64 The EDELWEISS-II experiment
for the small amounts of energy deposit and does not inherently depend on
the type of interaction.
The main problem of the heat trigger is the search of the corresponding ionization
signal which occurs before the heat signal because of its very fast risetime.
This problem has been worked out in [160]. The conclusion is that the maximum
time interval between an ionization and a heat signal is 20 ms. Thus, as soon as a
heat signal passes the threshold, the acquisition software looks back up to 20 ms in
the ionization signal buffer for the corresponding signals. This is made by comparing
the data with a reference event built during the calibration runs. Once the event
with the highest amplitude is found, all other events are synchronized to this one
and saved on disk.
The data are saved in different formats per run:
• raw files: There are some event files per run, with all the necessary information
for the analysis.
• log file: There is one “log” file, which is the monitoring file of the DAQ.
• seuils file: From the Run 10 on of EDELWEISS-II, there is one “seuils” file,
which enumerates regularly the thresholds applied for each bolometer during
the physics run. This threshold can be changed during a run, this is the
so-called adaptative threshold.
• ntp file: There is one “ntp” file per run. Ntp files are sort of pre-analysed event
files to monitor the behavior of bolometers.
3.1.8 Online monitoring
The ever growing number of bolometers (and channels) leads to develop an automatic
online monitoring to supervise the bolometers’behavior during data acquisition and
to fast and timely check the quality of the acquired data. To get acquainted with
the bolometer system of EDELWEISS-II, for which coincidences with the muon veto
are later described, cf. Chapters 5 and 6, the online monitoring software was tackled
within this work during two 3-month stays at the IRFU † CEA/Saclay (France) in
winter 2007 and winter 2008, and was further developed by Eric Armengaud.
The monitoring software transforms the latest ntp files into ROOT-files [162]
and creates usual plots, which are then published online on an internal EDELWEISS
website [163]. All data remain local on a computer in the data acquisition room at
LSM. The bolometer monitoring runs every hour. These plots are as various as the
global rate of the system, bolo-per-bolo event rates (Figure 3.8a), thresholds per bolo
(Figure 3.8b), ionization signal from guard vs. center per bolo (Figure 3.8c), heat
from one temperature sensor vs. the other one for NbSi bolometer (Figure 3.8d),
heat vs. ionization (cf. Chapter 6), baselines ... The monitoring script also copies
every night the run files of the day to the IN2P3 ‡ Computer Center in Lyon, where
all EDELWEISS data are stored, and provides a backup for CEA/Saclay.
† IRFU: Institut de Recherche sur les lois Fondamentales de l’Univers, CEA: Commissariat à
l’Énergie Atomique.
‡ IN2P3: Institut National de Physique Nucléaire et de Physique des Particules