TheEuropean Underground Rare Event Calorimeter Array (EURECA) is a planneddark matter search experiment usingcryogenic detectors and an absorber mass of up to 1 tonne. The project will be built in theModane Underground Laboratory and will bring together researchers working on theCRESST andEDELWEISS experiments.^[1][2]

EURECA featured prominently in theASPERA road map of Astroparticle Physics experiments in Europe.^[3]

Dark matter is one of the significantunsolved problems in modern science. There is considerable evidence fromastronomy andcosmology that a significant fraction of the mass of the Universe, and of galaxies is made up of non-luminous material. The nature of dark matter is currently unknown. However a popular hypothesis is that it consists ofWeakly Interacting Massive Particles (WIMPs), particles with a large mass, but which only interact with ordinary matter through theweak nuclear force, so the majority that pass through the Earth do not hit a single atom. The aim of dark matter search experiments such as EURECA is to test this hypothesis by searching for WIMP dark matter interactions. WIMPs are predicted to exist bysupersymmetry theory, which predicts a wide range of scattering cross-sections down to 10⁻¹⁰pb, corresponding to an interaction rate of ~1 event per year in a 1 tonne detector.^[4] Existing experiments such asCRESST andEDELWEISS have already ruled out higher interaction rates, but EURECA will search down to this lower limit.

Cryogenic dark matter experiments use particle detectors operating at millikelvin temperatures to search for the elastic scattering of WIMPs of an atomic nuclei. A particle interaction inside an absorber crystal will create a large number ofphonons, these thermalise inside athermometer on the crystal surface, which records the rise in temperature. Such cryogenic detectors are used as they combine a high sensitivity with a low energy threshold and excellent resolution.

Dark matter experiments are located in deep underground laboratories, and use extensive shielding to reduce the background radiation levels fromcosmic rays. Early experiments were limited by the remaining background due to radioactive impurities close to the detectors. Therefore the second phase of CRESST and EDELWEISS used new detectors capable of distinguishing electron recoil events from nuclear recoils. Electron recoils are produced byalpha,beta andgamma particles which account for the vast majority of background events. WIMPs (and also neutrons) produce nuclear recoils. This is done by measuring an additional signal, which is much higher for electron recoils than nuclear recoils. CRESST detectors measure thescintillation light produced in a CaWO₄ or ZnWO₄ absorber crystal. EDELWEISS detectors measure theionization produced in a semiconductinggermanium crystal.

EURECA will take this cryogenic detector technology pioneered by CRESST and EDELWEISS further by building a 1 tonne absorber mass made up from a large number of cryogenic detector modules. The experiment plans to use a range of detector materials. This provides a way to show if a positive signal is due to dark matter, as the event rate is expected to scale with theatomic mass of the target nuclei. Whereas the event rate fromneutrons will be higher for lighter nuclei.

The EURECA collaboration includes the member institutions ofCRESST,EDELWEISS, andROSEBUD dark matter experiments, and some new members. These are:

• Oxford University
• Commissariat à l'Énergie Atomique
• Centre National de la Recherche Scientifique
• Max-Planck-Institut für Physik München
• Technische Universität München
• Universität Tübingen
• Universität Karlsruhe
• Forschungszentrum Karlsruhe
• JINR
• Universidad de Zaragoza
• INR Kiev
• CERN

The collaboration spokesman is Gilles Gerbier. The experiment will be built in theModane Underground Laboratory, in theFréjus road tunnel between France and Italy, the deepest underground laboratory in Europe.

EURECA researchers are currently involved in data taking and analysis for CRESST and EDELWEISS. In addition, there are various R&D activities under way associated with scaling up the detector technology to a 1-tonne scale. These include:

• Cryogenics: EURECA will require a one tonne mass to be cooled to millikelvin temperature. This will be done using large scale cryogenic technology, as used to coolgravitational wave experiments and the 27 kmLHC accelerator ring.
• Scintillators: Research is being carried out to develop large radiopure absorber crystals with good scintillation properties at low temperatures.^[5]
• Detector readout: EURECA will require hardware and software to read-out the signals from 1000+ detector channels.

• Dark Matter
• Weakly Interacting Massive Particle
• EDELWEISS
• CRESST

• EURECA Collaboration home page
• ASPERA: Astroparticle physics European network

• Experiments for dark matter search

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