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

tel-00724955, version 1 - 23 Aug 2012
2.3 Direct detection 45
the DAMA/NaI which accumulated an exposure of 0.29 ton-year, are also shown.
The improved signal due to increased statistics is clear in this plot and an annual
modulation is evident. Other possible systematic effects such as temperature effects
on the noise of the photomultiplier tubes, humidity related backgrounds, radon or
other systematic effects has not been conclusively established.
Assuming a spin-independent interaction and a WIMP mass of tens of GeV/c 2
or higher, the WIMP-nucleus cross section extracted from the annual modulation
in the DAMA/NaI experiment would correspond to ∼ 10 −5 pb. This claim has
been ruled out by previous CDMS experiment results [123] and by many other
experiments, including various targets and radically different techniques, such as
the XENON 10 experiment [116]. Nevertheless, due to the insufficiently-low energy
threshold of the majority of the other experiments, it has been proposed that light
WIMPs (∼ 10 GeV/c 2 ) could cause the observed modulation and still be undetected
by the other experiments [128, 129]. Recently, the COUPP collaboration, using
an improved bubble chamber technology, has ruled out the WIMP hypothesis for
spin-dependent WIMP-nucleus interactions [130]. The remaining possibility that
low-mass WIMPs undergo spin-independent interactions has been ruled out more
recently by the CoGeNT collaboration [131] employing a new type of Germanium
radiation detector with a very low electronic noise [132]. And finally a latest attempt
to reconcile the detection of annual modulation observation of DAMA experiment
and null results from all other experiments was to introduce inelastic dark matter.
Inelastic dark matter model explored the possibility of an altered kinematics of the
collision between the χ and the nuclei. This scenario seems to be also ruled out by
the noble liquid Xenon detector of the ZEPLIN-II experiment [133].
The DAMA results have not been solved yet. The collaboration has not been
able to identify any other systematic effects capable of producing this signal. However,
the claim that this signal is the result of dark matter interactions is in direct
conflict with any other experiments. The DAMA results may be an artificial, one
dare say a false, result or may lead to a non-MSSM dark matter candidate, as long
as the results are not reproduced, the claim is not conclusive.
Direct detection of dark matter encompasses all those experiments that search for
a dark matter particle interacting directly with the detector, via elastic scattering,
for example, with a target nucleus causing a nuclear recoil of about 15 keV. Indirect
detection experiments search for a non-WIMP particle originating from WIMPs that
interact with the detector. In collider experiments a new particle may be produced
and be detectable in a twist of looking for “missing energy” or missing transfer
momentum.
However, a measurement of the couplings is highly unlikely in collider, and it
will not be possible to determine if the “missing particle” has the necessary stability
to be a “freeze out” product from the Big-Bang. Moreover, the production rate and
detectability of WIMPs at colliders depends primarily upon the masses of the WIMP
and related new particles: If the particles are too heavy, they cannot be produced.
Thus, primary annihilation processes that set the relic density in some WIMP models
are temperature-dependent. The annihilation rates of such models are greatly
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