The European Underground Rare Event Calorimeter Array (EURECA) is a planned

dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

search experiment using

cryogenic detectors Cryogenic particle detectors operate at very low temperature, typically only a few degrees above absolute zero. These sensors interact with an energetic elementary particle (such as a photon) and deliver a signal that can be related to the type of ...

and an absorber mass of up to 1 tonne. The project will be built in the

Modane Underground Laboratory The Modane Underground Laboratory (LSM) (french: Laboratoire Souterrain de Modane; also known as the Fréjus Underground Laboratory) is a subterranean particle physics laboratory located within the Fréjus Road Tunnel near Modane, France. It is jo ...

and will bring together researchers working on the CRESST and

EDELWEISS EDELWEISS (Expérience pour DEtecter Les WIMPs En Site Souterrain) is a dark matter search experiment located at the Modane Underground Laboratory in France. The experiment uses cryogenic detectors, measuring both the phonon and ionization signals ...

experiments. EURECA featured prominently in the

ASPERA Aspera may refer to: Music * Aspera (band), an American indie rock band * ''(a)spera'', a 2009 album by Mirah * Above Symmetry, a Norwegian progressive metal band originally known as Aspera * "Aspera", the lead track from ''We Will Become Like Bir ...

road map of Astroparticle Physics experiments in Europe.

Dark matter

Dark matter is one of the significant

unsolved problems List of unsolved problems may refer to several notable conjectures or open problems in various academic fields: Natural sciences, engineering and medicine * Unsolved problems in astronomy * Unsolved problems in biology * Unsolved problems in c ...

in modern science. There is considerable evidence from

astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...

and

cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount (lexicographer), Thomas Blount's ''Glossographia'', and in 1731 taken up in ...

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 of

Weakly Interacting Massive Particles Weakly interacting massive particles (WIMPs) are hypothetical particles that are one of the proposed candidates for dark matter. There exists no formal definition of a WIMP, but broadly, a WIMP is a new elementary particle which interacts via gra ...

(WIMPs), particles with a large mass, but which only interact with ordinary matter through the

weak nuclear force In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction, ...

, 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 by

supersymmetry In a supersymmetric theory the equations for force and the equations for matter are identical. In theoretical and mathematical physics, any theory with this property has the principle of supersymmetry (SUSY). Dozens of supersymmetric theories e ...

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. Existing experiments such as CRESST and

have already ruled out higher interaction rates, but EURECA will search down to this lower limit.

Cryogenic dark matter searches

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 of

phonons In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phonon is an excited state in the quantum mechanical ...

, these thermalise inside a

thermometer A thermometer is a device that temperature measurement, measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a merc ...

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 from

cosmic rays Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

. 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 by

alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...

beta Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...

and

gamma Gamma (uppercase , lowercase ; ''gámma'') is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter re ...

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 the scintillation light produced in a CaWO₄ or ZnWO₄ absorber crystal. EDELWEISS detectors measure the

ionization Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

produced in a semiconducting

germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors s ...

crystal.

EURECA

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 the

atomic mass The atomic mass (''m''a or ''m'') is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1&nbs ...

of the target nuclei. Whereas the event rate from

neutrons The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...

will be higher for lighter nuclei. The EURECA collaboration includes the member institutions of CRESST,

, and

ROSEBUD Rosebud may refer to: * Rose bud, the bud of a rose flower Arts * The name of Jerry Garcia's guitar from 1990 until his death in 1995. * In the 1941 film ''Citizen Kane'', the last words of Charles Foster Kane and an overall plot device. * "Ros ...

dark matter experiments, and some new members. These are: *

Oxford University Oxford () is a city in England. It is the county town and only city of Oxfordshire. In 2020, its population was estimated at 151,584. It is north-west of London, south-east of Birmingham and north-east of Bristol. The city is home to the ...

Commissariat à l'Énergie Atomique The French Alternative Energies and Atomic Energy Commission or CEA (French language, French: :fr:Commissariat à l'énergie atomique et aux énergies alternatives, Commissariat à l'énergie atomique et aux énergies alternatives), is a French pub ...

Centre National de la Recherche Scientifique The French National Centre for Scientific Research (french: link=no, Centre national de la recherche scientifique, CNRS) is the French state research organisation and is the largest fundamental science Basic research, also called pure research o ...

* Max-Planck-Institut für Physik München *

Technische Universität München The Technical University of Munich (TUM or TU Munich; german: Technische Universität München) is a public research university in Munich, Germany. It specializes in engineering, technology, medicine, and applied and natural sciences. Establis ...

* Universität Tübingen *

Universität Karlsruhe The Karlsruhe Institute of Technology (KIT; german: Karlsruher Institut für Technologie) is a public research university in Karlsruhe, Germany. The institute is a national research center of the Helmholtz Association. KIT was created in 2009 w ...

Forschungszentrum Karlsruhe The Karlsruhe Institute of Technology (KIT; german: Karlsruher Institut für Technologie) is a public university, public research university in Karlsruhe, Germany. The institute is a national research center of the Helmholtz Association. KIT wa ...

JINR The Joint Institute for Nuclear Research (JINR, russian: Объединённый институт ядерных исследований, ОИЯИ), in Dubna, Moscow Oblast (110 km north of Moscow), Russia, is an international research cen ...

Universidad de Zaragoza The University of Zaragoza, sometimes referred to as Saragossa University () is a public university with teaching campuses and research centres spread over the three provinces of Aragon, Spain. Founded in 1542, it is one of the oldest universiti ...

INR Kiev
*

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gene ...

The collaboration spokesman is Gilles Gerbier. The experiment will be built in the

Modane Modane (; ) is a Communes of France, commune in the Savoie Departments of France, department in the Auvergne-Rhône-Alpes Regions of France, region in southeastern France. The commune is in the Maurienne Valley, and it also belongs to the Vanoise ...

Underground Laboratory, in the

Fréjus road tunnel The Fréjus Road Tunnel is a tunnel that connects France and Italy. It runs under Col du Fréjus in the Cottian Alps between Modane in France and Bardonecchia in Italy. It is one of the major trans-Alpine transport routes between France and Ital ...

between France and Italy, the deepest underground laboratory in Europe.

R&D activities

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 In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...

: 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 cool

gravitational wave Gravitational waves are waves of the intensity of gravity generated by the accelerated masses of an orbital binary system that propagate as waves outward from their source at the speed of light. They were first proposed by Oliver Heaviside in 1 ...

experiments and the 27 km

LHC The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundre ...

accelerator ring. *

Scintillators A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate (i.e. re-emit the absorbe ...

: Research is being carried out to develop large radiopure absorber crystals with good scintillation properties at low temperatures.Proceedings of the 1st International Workshop "Radiopure Scintillators for EURECA" (RPScint'2008
arxiv:0903.1539
/ref> *Detector readout: EURECA will require hardware and software to read-out the signals from 1000+ detector channels.

References

External links