Background studies for the EDELWEISS dark matter experiment

The EDELWEISS-II collaboration has completed a direct search for WIMP dark matter using cryogenic Ge detectors (400 g each) and 384 kg$\times$days of effective exposure. A cross-section of $4.4 \times 10^{-8}$ pb is excluded at 90% C.L. for a WIMP mass of 85 GeV. The next phase, EDELWEISS-III, aims to probe spin-independent WIMP-nucleon cross-sections down to a few $\times10^{-9}$ pb. We present here the study of gamma and neutron background coming from radioactive decays in the set-up and shielding materials. We have carried out Monte Carlo simulations for the completed EDELWEISS-II setup with GEANT4 and normalised the expected background rates to the measured radioactivity levels (or their upper limits) of all materials and components. The expected gamma-ray event rate in EDELWEISS-II at 20-200 keV agrees with the observed rate of 82 events/kg/day within the uncertainties in the measured concentrations. The calculated neutron rate from radioactivity of 1.0-3.1 events (90% C.L.) at 20-200 keV in the EDELWEISS-II data together with the expected upper limit on the misidentified gamma-ray events ($\le0.9$), surface betas ($\le0.3$), and muon-induced neutrons ($\le0.7$), do not contradict 5 observed events in nuclear recoil band. We have then extended the simulation framework to the EDELWEISS-III configuration with 800 g crystals, better material purity and additional neutron shielding inside the cryostat. The gamma-ray and neutron backgrounds in 24 kg fiducial mass of EDELWEISS-III have been calculated as 14-44 events/kg/day and 0.7-1.4 events per year, respectively. The results of the background studies performed in the present work have helped to select better purity components and improve shielding in EDELWEISS-III to further reduce the expected rate of background events in the next phase of the experiment.Comment: 15 pages, 9 figures, to be published in Astroparticle Physic

Latest Progress on the QUBIC Instrument

International audienceQUBIC is a unique instrument that crosses the barriers between classical imaging architectures and interferometry taking advantage from both for high sensitivity and systematics mitigation. The scientific target is the detection of the primordial gravitational waves imprint on the Cosmic Microwave Background which are the proof of inflation, holy grail of modern cosmology. In this paper, we show the latest advances in the development of the architecture and the sub-systems of the first module of this instrument to be deployed in Dome Charlie Concordia base - Antarctica in 2015

Optical modelling and analysis of the Q and U bolometric interferometer for cosmology

International audienceRemnant radiation from the early universe, known as the Cosmic Microwave Background (CMB), has been redshifted and cooled, and today has a blackbody spectrum peaking at millimetre wavelengths. The QUBIC (Q&U Bolometric Interferometer for Cosmology) instrument is designed to map the very faint polaristion structure in the CMB. QUBIC is based on the novel concept of bolometric interferometry in conjunction with synthetic imaging. It will have a large array of input feedhorns, which creates a large number of interferometric baselines. The beam from each feedhorn is passed through an optical combiner, with an off-axis compensated Gregorian design, to allow the generation of the synthetic image. The optical-combiner will operate in two frequency bands (150 and 220 GHz with 25% and 18.2 % bandwidth respectively) while cryogenically cooled TES bolometers provide the sensitivity required at the image plane. The QUBIC Technical Demonstrator (TD), a proof of technology instrument that contains 64 input feed-horns, is currently being built and will be installed in the Alto Chorrillos region of Argentina. The plan is then for the full QUBIC instrument (400 feed-horns) to be deployed in Argentina and obtain cosmologically significant results. In this paper we will examine the output of the manufactered feed-horns in comparison to the nominal design. We will show the results of optical modelling that has been performed in anticipation of alignment and calibration of the TD in Paris, in particular testing the validity of real laboratory environments. We show the output of large calibrator sources (50 ° full width haf max Gaussian beams) and the importance of accurate mirror definitions when modelling large beams. Finally we describe the tolerance on errors of the position and orientation of mirrors in the optical combiner

Optical modelling and analysis of the Q and U bolometric interferometer for cosmology

Remnant radiation from the early universe, known as the Cosmic Microwave Background (CMB), has been redshifted and cooled, and today has a blackbody spectrum peaking at millimetre wavelengths. The QUBIC (Q&U Bolometric Interferometer for Cosmology) instrument is designed to map the very faint polaristion structure in the CMB. QUBIC is based on the novel concept of bolometric interferometry in conjunction with synthetic imaging. It will have a large array of input feedhorns, which creates a large number of interferometric baselines. The beam from each feedhorn is passed through an optical combiner, with an off-axis compensated Gregorian design, to allow the generation of the synthetic image. The optical-combiner will operate in two frequency bands (150 and 220 GHz with 25% and 18.2 % bandwidth respectively) while cryogenically cooled TES bolometers provide the sensitivity required at the image plane. The QUBIC Technical Demonstrator (TD), a proof of technology instrument that contains 64 input feed-horns, is currently being built and will be installed in the Alto Chorrillos region of Argentina. The plan is then for the full QUBIC instrument (400 feed-horns) to be deployed in Argentina and obtain cosmologically significant results. In this paper we will examine the output of the manufactered feed-horns in comparison to the nominal design. We will show the results of optical modelling that has been performed in anticipation of alignment and calibration of the TD in Paris, in particular testing the validity of real laboratory environments. We show the output of large calibrator sources (50 ° full width haf max Gaussian beams) and the importance of accurate mirror definitions when modelling large beams. Finally we describe the tolerance on errors of the position and orientation of mirrors in the optical combiner