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EDELWEISS (Expérience pour DEtecter Les WIMPs En Site Souterrain) is a
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 located at 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 ...
in France. The experiment uses
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 ...
, measuring both the
phonon In physics, a phonon is a collective excitation in a periodic, Elasticity (physics), elastic arrangement of atoms or molecules in condensed matter physics, condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phon ...
and
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 ...
signals produced by particle interactions in
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 ...
crystals. This technique allows nuclear recoils events to be distinguished from electron recoil events. The EURECA project is a proposed future dark matter experiment, which will involve researchers from EDELWEISS and the CRESST dark matter search.


Dark matter

Dark matter is material which does not emit or absorb light. Measurements of the
rotation curves The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot, and ...
of
spiral galaxies Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''cosmic microwave background radiation In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all space ...
suggest it accounts for a significant fraction of the density of the Universe. A possible explanation of dark matter comes from
particle physics Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...
. WIMP (
Weakly Interacting Massive Particle 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 ...
) is a general term for hypothetical particles which interact only through the weak nuclear and
gravitational force In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong ...
. This theory suggests our galaxy is surrounded by a dark halo of such particles. EDELWEISS is one of a number of dark matter search experiments aiming to directly detect WIMP dark matter, by detecting the elastic scattering of a WIMP off an atom within a particle detector. As the interaction rate is so low, this requires sensitive detectors, good background discrimination, and a deep underground site (to reduce the background 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 ...
).


Experiment

EDELWEISS is located in the Modane underground laboratory, in the Fréjus road tunnel between France and Italy, below 1800m of rock. A 20 cm
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
shield reduces the gamma background, and a
polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
shield reduces the
neutron 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 beh ...
flux. All materials close to the detectors are screened for radiopurity. A
dilution refrigerator A 3He/4He dilution refrigerator is a cryogenics, cryogenic device that provides continuous cooling to temperatures as low as 2 Kelvin, mK, with no moving parts in the low-temperature region. The cooling power is provided by the heat o ...
is used to cool the detectors, built in the opposite orientation to most instruments with the detectors at the top and the refrigeration mechanism below. EDELWEISS uses high purity
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 ...
cryogenic bolometers cooled to 20 milliKelvin above absolute zero. The
phonon In physics, a phonon is a collective excitation in a periodic, Elasticity (physics), elastic arrangement of atoms or molecules in condensed matter physics, condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phon ...
and
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 ...
signals produced by a particle interaction are measured. This allows background events to be rejected as nuclear recoils events (produced by WIMP or neutron interactions) produce much less ionization than electron recoil events (produced by alpha, beta and gamma radiation). The detectors are similar to those used by the CDMS experiment. Simultaneous detection of ionization and heat with semiconductors at low temperature was an original idea by Lawrence M. Krauss,
Mark Srednicki Mark may refer to: Currency * Bosnia and Herzegovina convertible mark, the currency of Bosnia and Herzegovina * East German mark, the currency of the German Democratic Republic * Estonian mark, the currency of Estonia between 1918 and 1927 * Fin ...
and
Frank Wilczek Frank Anthony Wilczek (; born May 15, 1951) is an American theoretical physicist, mathematician and Nobel laureate. He is currently the Herman Feshbach Professor of Physics at the Massachusetts Institute of Technology (MIT), Founding Direc ...
. A major limitation of early detectors was the problem of surface events. Due to incomplete charge collection, a particle interaction near the surface of the crystal gave no ionization signal, so electron recoils near the surface could be mistaken for nuclear recoils. To avoid this, the collaboration developed new detectors with interdigitised electrodes. Different voltages are applied to a series of electrodes so the direction of electric field is different near the surface of the crystal, allowing over 99.5% of surface events to be rejected.


Results

The results from the first phase of the experiment (EDELWEISS I) were published in 2005, excluding WIMP dark matter with an interaction cross-section above (at ≈85 GeV). EDELWEISS-II ran 2009–10 with 10 detectors, that is, 4 kg of detector mass (for a total effective exposure of 384 kg· d) limiting high mass and low mass WIMPs, and axions. A cross-section of is excluded at 90% C.L. for WIMP mass of 85 GeV. (Just above projected CDMS results in Fig A.) EDELWEISS-III had 40 detectors. EDELWEISS-III conducted first science run 2014-2015 with results published in 2016. EURECA design work will continue for operation after the EDELWEISS-III run. It is planned that EURECA would start operating after 2017.


Collaboration

EDELWEISS is a collaboration of the following member institutions:


CEA – Commissariat à l'Énergie Atomique

* IRFU - Institut de Recherche sur les Lois Fondamentales de l'Univers * IRAMIS - Institut Rayonnement Matière de Saclay


CNRS – Centre National de la Recherche Scientifique

* CSNSM - Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Orsay * IPNL - Institut de Physique Nucléaire de Lyon * Institut NÉEL, Grenoble * IAS -
Institut d'Astrophysique Spatiale The Institut d'astrophysique spatiale (IAS; English: Institute of Space Astrophysics) is a French research institute supporting advanced research in aerospace and astrophysics. It is located in Orsay, just south of Paris. It is a public resear ...
, Paris


Institutions outside France

*
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 ...
, Germany *
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 ...
, Germany *
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 ...
– Joint Institute for Nuclear Research, Dubna, Russia *
University of Oxford , mottoeng = The Lord is my light , established = , endowment = £6.1 billion (including colleges) (2019) , budget = £2.145 billion (2019–20) , chancellor ...


References


External links


EDELWEISS Collaboration home page

EURECA Collaboration home page
{{DEFAULTSORT:Edelweiss Experiments for dark matter search