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

tel-00724955, version 1 - 23 Aug 2012
2
40 Detecting the WIMP
regime, even at very large WIMP-search exposures. This requires a powerful particle
identification technique that operates at low energies, but the benefits of lowbackground
operation allow one to extract enormous sensitivity from relatively small
detector exposures in this way.
Most modern direct-detection experiments use event-by-event discrimination techniques
to identify nuclear recoils from WIMPs, or neutrons, among a far larger rate of
electron recoils from radioactive decay and cosmogenic processes. Some experiments,
notably bubble chambers and other phase-transition detectors, use the difference in
dE/dx between electron- and nuclear-recoil tracks to make their detectors unresponsive
to electron recoils, thus achieving a particularly simple sort of event-by-event
discrimination. Discrimination is more commonly accomplished by measuring each
event in two or more distinct detection channels and using their ratio to identify
the recoil type. When the recoil occurs, the energy is partitioned in the ionization,
the heat/phonons and the scintillation channels. In Figure 2.2, the main detection
techniques are shown around a triangle that depicts the energy from the interaction
of a WIMP-nuclear recoil. These channels differ enormously in the mean nuclear recoil
energy needed to create the individual quanta: A few meV per phonon, ∼ 10 eV
per charge carrier, and ∼ 100 eV per scintillation photon. Each detection technique
exploits one or more of this channels or degrees of freedom to make the discrimination
between nuclear recoils (neutrons and WIMPs) and electron recoils (majority
of backgrounds).
Xe, Ar,
Ne
NaI, Xe,
Ar, Ne
ZEPLIN II, III
XENON
WARP
ArDM
SIGN
LUX
NAIAD
ZEPLIN I
DAMA
XMASS
DEAP
Mini-CLEAN
Scintillation
Few % of Energy
Ge, CS2 , C3F8 DRIFT
IGEX
COUPP
~20% of Energy
Ionization
Heat -
Phonons
CRESST II
ROSEBUD
CaWO4 , BGO
ZnWO 4 , Al 2 O 3 …
~100% of Energy
CDMS
EDELWEISS
CRESST I
Al 2 O 3 , LiF
Ge, Si
Figure 2.2: Main detection techniques to track a WIMP signal. The triangle depicts
the energy after a nuclear recoil interaction from a WIMP, each corner represents
a channel where the energy from the interaction appears. Each detection technique
exploits one or more of these channels. Most of the energy goes into phonons and
ionization, the two channels used by CDMS and EDELWEISS. Figure from [115].