EDELWEISS
Encyclopedia
EDELWEISS is a dark matter
search experiment located in the Modane
Underground Laboratory. The experiment uses cryogenic detectors, measuring both the phonon
and ionization
signals produced by particle interactions in germanium
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.
suggest it accounts for a significant fraction of the density of the Universe.
A possible explanation of dark matter comes from particle physics
. WIMP (Weakly Interacting Massive Particle) is a general term for hypothetical particles which interact only through the weak nuclear
and gravitational force
. 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).
shield reduces the gamma background, and a polyethylene
shield reduces the neutron
flux. All materials close to the detectors are screened for radiopurity. A dilution refrigerator
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
cryogenic bolometers cooled to ~20mK temperature. The phonon
and ionization
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 and Frank Wilczek
.
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 problem, the collaboration have 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. This allows over 99.5% of surface events to be rejected.
The results from the first phase of the experiment (EDELWEISS I) have been published, excluding WIMP dark matter with an interaction cross-section above ~10−6pb. The current phase - EDELWEISS II – is now taking data. The experiment will run through 2010, after which the EURECA experiment plans to start construction in the Modane laboratory.
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
search experiment located in the Modane
Modane
Modane is a commune in the Savoie department in the Rhône-Alpes region in southeastern France.It was part of the Kingdom of Sardinia until 1860.-Transportation:...
Underground Laboratory. The experiment uses cryogenic detectors, measuring both the phonon
Phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, such as solids and some liquids...
and ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
signals produced by particle interactions in germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
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 of spiral galaxies suggest it makes up the majority of the mass of galaxies; and precision measurements of the cosmic microwave background radiationCosmic microwave background radiation
In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
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
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
. WIMP (Weakly Interacting Massive Particle) is a general term for hypothetical particles which interact only through the weak nuclear
Weak interaction
Weak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
and gravitational force
Gravitation
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...
. 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).
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 leadLead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
shield reduces the gamma background, and a polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
shield reduces the neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
flux. All materials close to the detectors are screened for radiopurity. A dilution refrigerator
Dilution refrigerator
A dilution refrigerator is a cryogenic device first proposed by Heinz London. Its refrigeration process uses a mixture of two isotopes of helium: helium-3 and helium-4...
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
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
cryogenic bolometers cooled to ~20mK temperature. The phonon
Phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, such as solids and some liquids...
and ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
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
Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search is a series of experiments designed to directly detect particle dark matter in the form of WIMPs. Using an array of semiconductor detectors at millikelvin temperatures, CDMS has set the most sensitive limits to date on the interactions of WIMP dark matter with...
experiment. Simultaneous detection of ionization and heat with semiconductors at low temperature was an original idea by Lawrence M. Krauss
Lawrence M. Krauss
Lawrence Maxwell Krauss is an American theoretical physicist who is professor of physics, Foundation Professor of the School of Earth and Space Exploration, and director of the Origins Project at the Arizona State University. He is the author of several bestselling books, including The Physics of...
, Mark Srednicki and Frank Wilczek
Frank Wilczek
Frank Anthony Wilczek is a theoretical physicist from the United States and a Nobel laureate. He is currently the Herman Feshbach Professor of Physics at the Massachusetts Institute of Technology ....
.
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 problem, the collaboration have 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. This allows over 99.5% of surface events to be rejected.
The results from the first phase of the experiment (EDELWEISS I) have been published, excluding WIMP dark matter with an interaction cross-section above ~10−6pb. The current phase - EDELWEISS II – is now taking data. The experiment will run through 2010, after which the EURECA experiment plans to start construction in the Modane laboratory.
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, Paris
Institutions outside France
- Universität Karlsruhe, Germany
- Forschungszentrum Karlsruhe, Germany
- JINR – Joint Institute for Nuclear Research, Dubna, Russia
- University of OxfordUniversity of OxfordThe University of Oxford is a university located in Oxford, United Kingdom. It is the second-oldest surviving university in the world and the oldest in the English-speaking world. Although its exact date of foundation is unclear, there is evidence of teaching as far back as 1096...
See also
- Commissariat à l'énergie atomiqueCommissariat à l'Énergie AtomiqueThe Commissariat à l'énergie atomique et aux énergies alternatives or CEA, is a French “public establishment related to industrial and commercial activities” whose mission is to develop all applications of nuclear power, both civilian and military...
- Centre National de la Recherche ScientifiqueCentre national de la recherche scientifiqueThe National Center of Scientific Research is the largest governmental research organization in France and the largest fundamental science agency in Europe....
- Dark MatterDark matterIn astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
- Weakly Interacting Massive Particle
- Cryogenic Dark Matter SearchCryogenic Dark Matter SearchThe Cryogenic Dark Matter Search is a series of experiments designed to directly detect particle dark matter in the form of WIMPs. Using an array of semiconductor detectors at millikelvin temperatures, CDMS has set the most sensitive limits to date on the interactions of WIMP dark matter with...
- EURECA
- CRESST