Institutions
Location
Canfranc underground laboratory
Laboratory 1 at 675 m.w.e.
Years
1989-1991
Description
It was an experiment performed at Canfranc to further investigate a small, unexplained coincidence effect (found in a previous experiment in the Frejus tunnel) close to the region where neutrinoless 0+ to 2+ 76Ge double beta decay should be expected.
The experimental setup consisted of a 208 cm3 ultralow background HPGe detector surrounded by 14 hexagonal NaI scintillators (4p geometry). They were placed within a low background shielding of 25 cm lead, 5 cm borated polyethylene, a PVC box (silicone sealed and flushed with nitrogen), 2 mm cadmium sheets and 20 cm of paraffin at the Canfranc underground laboratory.
A coincidence signal (the two electron energy at the germanium detector in coincidence with a 559.1 keV de-excitation photon in one NaI scintillator) was searched. After 6062.5 hours of counting time such coincidence signal was not observed and the previous Frejus peak was rejected as a neutrinoless double beta effect at the confidence level of 95%.
Institutions
Location
Phase 1: Homestake (4000 m.w.e.), Baksan (660 m.w.e.) and Canfranc (Laboratory 2 at 1380 m.w.e.)
Phase 2: Canfranc (Laboratory 3 at 2450 m.w.e.) and Baksan (660 m.w.e.)
Years
Phase 1: 1991-1993
Phase 2: 1994-2000
Description
The International Germanium EXperiment (IGEX) is a search for the neutrinoless double beta decay of 76Ge employing large amounts of HPGe detectors, isotopically enriched to 86% in 76Ge.
In the first phase of the experiment three detectors of 0.7 kg active volume each were operated: one in the Homestake gold mine (4000 m.w.e.), other in the Baksan Neutrino Observatory (660 m.w.e.) and the other in the Canfranc underground laboratory (Laboratory 2 at 1380 m.w.e.). A conservative lower bound on the neutrinoless half-life of about 1024 years was derived.
In the second phase, three large detectors (2kg each) were fabricated (with improvements derived from the analysis of data of Phase 1). They are installed in the Canfranc underground laboratory (Laboratory 3 at 2450 m.w.e.) inside a low background shielding consisting of 40 cm of lead, a PVC box (silicone sealed and flushed with nitrogen), 2mm of cadmium, 20 cm of polyethilene and an active veto (plastic scintillators). A pulse shape discrimination (PSD) technique capable to distinguish single site events (bb decay events for example) from multisite events (the most dominant background events) is implemented. New limits on the neutrinoless half-life and the neutrino mass parameter are obtained.
Institutions
Location
Canfranc underground laboratory
Laboratory 1 at 675 m.w.e.
Years
1991-1992
Description
The experiment was a search for the double beta (b+b+) and the electron-positron conversion (ECb+) decay modes of 78Kr using a ionization chamber (IC) with kripton gas. The IC (a high pressure, high resolution chamber made for this experiment) was filled with kripton gas isotopically enriched up to 94% in 78Kr.
The experimental device consisted of the ionization chamber (to record the positrons signal) placed within a hexagonal array of six large NaI scintillators (to record, in coincidence, the 511 keV annihilation photons). The multidetection system was installed in the Canfranc underground laboratory (Laboratory 1) inside a 20 cm of lead shielding.
From the analysis of the coincidence spectra half-life limits for both processes (b+b+ and ECb+) were obtained.
Institutions
Location
Canfranc underground laboratory
Laboratory 1 at 675 m.w.e.
Years
1990-1992
Description
Cosme was an experiment to search for cold dark matter particles with an ultralow background germanium detector. The detector consisted of a small hyperpure natural germanium crystal (44 cm3 active volume) with excellent performances at low energy: 1.6 keV threshold energy and 0.43 keV FWHM resolution (at 10.4 keV). It was placed within a low background shielding of 30 cm lead, a PVC box (silicone sealed and flushed with nitrogen), 1mm cadmium sheets and 20 cm of paraffin at the Canfranc underground laboratory.
A method of filtering the microphonic noise based on the simultaneous use of two different shaping times in the processing of the signal was implemented.
Contour limits for cross sections and masses of dark matter particles interacting with Ge nuclei through spin-independent interactions were derived for a total exposure of 130.7 kg day.
Location
Sierra Grande mine (Argentina)
1000 m.w.e.
Years
1994-1997
Description
DEMOS was an experimental search of distinctive signals of WIMPs carried out at the Sierra Grande mine (Argentina) with an ultralow background germanium detector. The detector consisted of a 1 kg natural germanium detector with 4 keV threshold energy and 1.2 keV FWHM resolution (at 10.4 keV). It was installed underground inside a low background shielding consinting of 40 cm lead, a plastic box (silicone sealed and flushed with nitrogen), 3 mm Cadmium sheets and 20 cm paraffin blocks.
The same microphonics filtering method used in COSME experiment was also applied.
The analysis of the 830.5 kg day of data recorded does not show any indication of annual/daily modulation effects. Contour limits for cross section and masses of spin-independent interacting WIMPs were derived.
Institutions
Location
Canfranc underground laboratory
Laboratory 3 at 2450 m.w.e.
Years
1998-1999
Description
The COSME ionization detector that had already been used in Cold Dark Matter searches (see COSME experiment) was reinstalled in better experimental conditions in February 1998 at the Canfranc underground laboratory (Laboratory 3 at 2450 m.w.e.) with the double aim of axion and WIMP detection. The new improved shielding is shared with the three IGEX detectors and consists of (from inside to outside): 40 cm of lead, a PVC box (silicone sealed and flushed with nitrogen), 2 mm of cadmium, plastic scintillators working in anticoincidence with the Ge detectors and 20 cm of polyethylene.
Besides the passive shielding, several software rejection techniques have been used. These are the anticoincidence with the muonic vetoes, a time filtering which enables us to reject events abnormally accumulated in time and a filtering based on the simultaneous use of two different shaping times in the processing of the signal.
The new experimental conditions, besides the fact of the intrinsic activity decrease of the detector due to its long underground storage, have allowed reducing the low energy background by about one order of magnitude from the previous running of the detector.
Exclusion plots in the paramatric space (mass versus cross section) for WIMPS and axions are derived.
Institutions
Location
Canfranc underground laboratory
Laboratory 3 at 2450 m.w.e.
Years
1999-
Description
The IGEX detectors had the initial objective of the detection of the double beta decay of 76Ge (see IGEX experiment).
At the end of 1999 certain modifications were made to adapt the detectors to the detection at low energy where the signal of WIMPs is relevant. The shielding, shared by three IGEX detectors (2 kg germanium detectors isotopically enriched to 86% in 76Ge) and the COSME detector, included from inside to outside 40 cm of lead, a PVC box (silicone sealed and flushed with nitrogen), 2 mm of cadmium, plastic scintillators working in anticoincidence with the Ge detectors and 20 cm of polyethylene.
In additon to the time filtering that eliminates abnormally accumulated events in time, a discrimination technique according to the shape of the event pulse when coming out of the amplifier was implemented. This relatively new technique (PSD), already used in IGEX double beta, allows an optimal discrimination of nondesirable events coming from the electronic noise and identifiable through its pulse shape as a random fluctuation of the base line.
At July 2001 the shielding was modified. Now, it includes only one 2 kg germanium detector inside a more efficient neutron shielding.
These techniques of passive and active shielding, along with the extreme radiopurity of the detectors and their components, allow us to reach a low energy background as well as a low enough threshold which are unique in this type of detectors. So, very stringent countour limits for cross sections and masses of dark matter particles interacting with Ge nuclei trhough spin-independent interactions are derived.
Institutions
Location
Canfranc underground laboratory
Laboratory 1 at 675 m.w.e.
Years
1992-1995
Description
NaI32 was an experiment to search for cold dark matter particles with a set of three NaI scintillators of 10.7 kg each. The main objective of the experiment was to search for distinctive features of the dark matter signal, like its expected annual modulation. Moreover, the 100% isotopic contents on A-odd isotopes of NaI scintillators make them very sensitive to spin-dependent interactions.
The NaI scintillators were made by BICRON with low background specifications; the crystals are coupled to a photomultiplier EMI9765 by a 3-inch quartz window. They were installed in the Canfranc underground laboratory inside a shielding consisting of 3-9 mm copper sheets, 20 cm of lead, a PVC box (silicone sealed and flushed with nitrogen), 1mm cadmium and 20 cm paraffin. Coincidences between the detectors were removed by software. Events arriving in bursts were also removed.
Bounds on cross sections and masses of WIMPs for an exposure of 4613.6 kg day both for spin-independent and spin-dependent WIMP-matter interactions were derived with the standard method of comparing the observed rate with the expected signal. The analysis of the data corresponding to 1342.8 kg day of exposure does not show any indication of annual effects. The nonobservance of such modulation has been used to draw more stringent exclusion plots than those derived from the standard method.
Location
Canfranc underground laboratory
Laboratory 3 at 2450 m.w.e.
Years
2000-
Description
ANAIS is a large mass scintillators experiment (107 kg NaI) planned to investigate seasonal modulation effects of WIMPs. With the aim to improve the elements which determine the sensitivity of this kind of experiments (energy threshold and radiactive background at threshold), a prototype experiment with a single 10.7 kg crystal is being developed in the Canfranc Underground Laboratory. Several changes on the detector are being performed: a new external teflon part of photomultiplier has been installed and it is planned to employ new ultra-low background photodiodes and to couple crystals through ligth guides to photomultipliers placed outside the internal shielding. The shielding consists of 30 cm of lead, 2 mm of cadmium and 40 cm of polyethylene and borated water. A sealed box in PVC maintained at overpressure by the injection of N2 prevents the instrusion of radon and an active veto covers the set-up.
A noise rejection technique according to the shape of the pulses (registered in a digital oscilloscope) allows to reduce the threshold energy down to 4 keV. Monitoring and stabilisation of several parameters such as temperatures, radon level or gain will be done.
Institutions
Location
Canfranc underground laboratory
Laboratory 3 at 2450 m.w.e.
Years
1998-
Description
ROSEBUD (Rare Objects SEarch with Bolometers UndergrounD) is an experiment aiming at the direct search of cold dark matter (WIMPs) by measuring the recoil energy transferred to the detector nuclei after a WIMP-nucleus elastic scattering. In ROSEBUD this deposited energy is measured through the following temperature increase in the crystal used as target kept at about 20 mK (thermally coupled to the mixing chamber of a 3He/4He dilution refrigerator). The corresponding changes in temperature (some microKelvin) are converted into changes in resistance in a germanium sensor (NTD), allowing for the required sensitivity for energy depositions of some hundreds of eV in small size crystals.
The cryostat and part of the acquisition electronics are lodged inside a Faraday cage in the new experimental hall of the Canfranc Underground Laboratory, at an equivalent depth of 2450 m.w.e. The external shielding consists of cadmium, lead and PVC box sealed to prevent the radon intrusion into the shielding. The inner shielding consists of OFHC copper and lead.
In the first phase of the experiment (1998-99) only sapphire (25 and 50 g) was used as absorber, being the main goal to reduce the radioactive background in the unfriendly cryogenic environment (down to about 8-10 evts/keV/kg/day at 100 keV at the end of 1999).
In the second phase of the experiment (started in 2000) bolometers of Germanium (67g), sapphire (50g) and Calcium Tungstate (54g) have been operated in Canfranc. For the first time three different absorbers worked in the same radioactive environment. Very good expectations come from the first underground heat-scintillation discrimination with a medium mass CaWO4 absorber. In a short measurement no recoil events were observed and alpha contamination was clearly discriminated from gamma/beta background. Previous test in Paris showed the discrimination of recoils with a neutron source. Currently, BGO is also under test for discrimination purposes.
You can also visit the Rosebud page at IAS (in French)
Institutions
Localition
CERN
Years
2000-
Description
CAST (CERN Axion Solar Telescope) is an international collaboration which aims the detection of solar axions using a prototype magnet for CERN's LHC collider. The experiment is based on the conversion of solar axions into X-ray photons (catalysed by the magnet) and the detection of the emerging converted photons. The conversion efficiency for axions increases as the square of the product of transverse magnetic field component and its length. This makes a 9 tesla, 10 m LHC prototype dipole magnet with straight beam pipes ideal for detecting axions.
To know all details of the experiment visit the home page of CAST.