(Rare Objects SEarch with Bolometers UndergrounD)


It is a collaboration, between the Institut d'Astrophysique Spatiale (IAS, France) and the University of Zaragoza (UNIZAR, Spain), dedicated to the development and optimization of scintillating bolometers to be used in Nuclear, Particle and Astroparticle Physics experiments. This framework included different running periods between the years 1997 and 2012 at the IAS facilities (ground laboratory) and also at the Canfranc Underground Laboratory (LSC). The work developed involved the study of different materials as target, analyzing its scintillating and bolometric properties, its particle discrimination capability, radiopurity, and its properties as particle detectors (response, linearity, energy resolution among others). Both institutions, IAS and UNIZAR, joined in 2006 at the EURECA (European Underground Rare Event Calorimeter Array) Collaboration and, in this context, ROSEBUD developed and tested scintillating bolometer prototypes that could be used in direct dark matter search experiments. ROSEBUD also joined in 2010 to the MultiDark (Multimessenger Approach for Dark Matter Detection) project, created to join efforts between the Spanish groups involved in dark matter research.

The ROSEBUD Collaboration was established in 1997 and since then its detection technique have been continuously evolving and progressing (from bolometers to scintillating bolometers). Efforts have focused on the study of different materials (dielectric and diamagnetic crystals) at low scale (due to the physical space available in the unit of sample of the dilution refrigerator limits the crystal mass to values lower than ≈100 g) that could be used as particle detectors developed as scintillating bolometer prototypes. Crystals used as targets were chosen considering its scintillation properties and particles discrimination capability at cryogenic temperatures (≈20 mK). In this context, ROSEBUD worked on three topics:

  1. development and test of scintillating bolometer prototypes that could be used as targets in direct dark matter search experiments;
  2. development of scintillating bolometers that, like LiF for instance, could be applied to monitor the neutron flux inside the experimental shielding of a cryogenic dark matter experiment; and
  3. choice of proper materials for EURECA construction in terms of radiopurity.

The IAS group contributed their great expertise in cryogeny and bolometers, and developed small (typically 50 - 100 g) scintillating bolometers of different materials (Ge, CaF2, SrF2, Al2O3, CaWO4, BGO (Bi4Ge3O12) and LiF, among others), and optimized their performances. The group of the University of Zaragoza contributed their long-standing experience in ultralow background and underground physics.

At the IAS we have a facility where systematic studies of scintillation at low temperatures were carried out, measuring the intensity and fluorescence spectra between 2 K and 300 K, analyzing its dependence on temperature and dopant concentration, in order to better understand the nature of the emission processes taking place. We also have a full cryogenic facility at IAS (dilution refrigerator, cryostat, lead shielding, Faraday cage, electronics, vacuum pumps, etc.) where we performed preliminary tests of the scintillating bolometers developed. We had another cryogenic facility in the Canfranc Underground Laboratory where, using the same dilution unit but an ultralow background cryostat (with modifications that include removal of some pieces and installation of internal lead and copper shields) in an ultralow background environment (lead and polyethylene shielding, radon removal system, etc), we performed the final tests and runs of the scintillating bolometers in underground. The Zaragoza group also has several HPGe detectors.

The ROSEBUD Collaboration made its last characterization measurements at the Canfranc Underground Laboratory (LSC) during the year 2012 and nowadays this Collaboration is over.

For details of the experimental set-up and results, background levels and detectors capabilities see publications and talks.