Search for SUSY particles in the galactic halo with FID detectors – FIDSUSY

The most recent measurements of the Cosmic Microwave Background
and of supernovae at large redshift, interpreted in the framework of the
concordance model, point to a Universe dominated by Dark Matter
(23%) and Dark Energy (70%). The necessity for a Dark Matter
component in the Universe is more urging now than ever since it was
first suggested in 1930, and the hypothesis that it is mostly made of a
new type of massive particles with weak interaction (WIMPs) has
consistently gained strength with time. SuperSymmetry theories provide
a natural candidate for WIMPs, the neutralino, with a wide range of
possible masses and interaction cross-sections. A particular set of
models (focus point), with cross-sections of the order of 10-8 pb and
masses between 50 and 800 GeV, constitute an extremely significant
goal for direct detection. The present project aims at exploring this
important region before the end of 2012 by building and operating an
array of 44 detectors of 800g with unprecedented performance and
reliability. The ANR contribution would consist in the production
of 40 of these detectors. The experimental facility and its upgrade
for accommodating the proposed program (operations at the Laboratoire
Souterrain de Modane, cryogenics, electronics and data acquisition)
would be provided by the EDELWEISS collaboration (CRNS, CEA, KIT,
Dubna and Oxford University). The detector design is based on that of the
Ge bolometers with double heat and ionisation readout with interleaved
electrodes (InterDigit, ID), developed in 2007-2008 with the support
from the ANR. EDELWEISS has confirmed since then their outstanding
interest for the domain of direct WIMP searches. From the measured
gamma and beta background rejection capabilities of ID detectors -
better than 1 in 30 000-, and from the measured rate of residual beta
and gamma within the environment of EDELWEISS II set up, we
anticipate that no background events are expected in a 3000 kg.d
exposure. Combined with an already achieved recoil energy threshold of
15 keV, this corresponds to the required sensitivity (5x10-9 pb) to reach
the quoted physics goal. However, the fiducial mass (160 g)
and the present number of detectors (between 10 and 15) would require
more than six years continuous running to obtain this result.
The proposed breakthrough is to build an array of 44 detectors of
800g where the entire surface is covered with interleaved detectors (Full
InterDigit technology, FID). With a fiducial mass of 660g per detectors,
this number would be sufficient to obtain this physics goal in six months.
This boost would enable EDELWEISS to come back to the forefront of
WIMP dark matter searches, a place that it actually occupied from 2002
to 2005, shortly after it aggressively increased detector size from 70
to 320g. The tests of the new generation of detectors has already begun
at LSM, with already the confirmation of the excellent surface rejection
performance of 400g FID prototypes, and the production of four 800g
prototypes for the final evaluation in Spring 2010 of the best readout
scheme for these detectors. With the support of the ANR for the
production of 40 detectors, the active mass available for WIMP
searches by EDELWEISS would be more than twice that proposed by our
American competitors CDMS, with the added advantage of a simpler,
cheaper and more robust design. The superior energy resolution and
background-rejection capabilities of FID detectors relative to xenon
detectors make it by far the most reliable technology to confirm any
dark-matter signal observation.