SIMPLE (Superheated Instrument for Massive ParticLe Experiments) is an experiment search for direct evidence of

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 ...

. It is located in a 61 m³ cavern at the 500 level of the Laboratoire Souterrain à Bas Bruit
LSBB
near

Apt Apt. is an abbreviation for apartment. Apt may also refer to: Places * Apt Cathedral, a former cathedral, and national monument of France, in the town of Apt in Provence * Apt, Vaucluse, a commune of the Vaucluse département of France * A ...

in southern

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

. The experiment is predominantly sensitive to

spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...

-dependent interactions 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 ...

(or WIMPs). SIMPLE is an international collaboration with members from

Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...

, and the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

Design

The SIMPLE detector is based on

superheated A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry steam. Superheated steam is used in steam turbines for electricity generation, steam engines, and in processes such as steam reforming. There are ...

droplet detectors (SDDs), a suspension of 1–2% superheated liquid C₂ClF₅ droplets (~30 μm radius) in a viscoelastic 900 ml gel matrix, which undergo transitions to the gas phase upon energy deposition by incident radiation. The

refrigerant A refrigerant is a working fluid used in the heat pump and refrigeration cycle, refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Ref ...

freon Freon ( ) is a registered trademark of the Chemours Company and generic descriptor for a number of halocarbon products. They are stable, nonflammable, low toxicity gases or liquids which have generally been used as refrigerants and as aerosol prop ...

, is used as the active mass. In effect, each droplet behaves as a miniature

bubble chamber A bubble chamber is a vessel filled with a superheated transparent liquid (most often liquid hydrogen) used to detect electrically charged particles moving through it. It was invented in 1952 by Donald A. Glaser, for which he was awarded the 196 ...

. Once a

nucleation In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that deter ...

has occurred, the acoustic shock wave is picked up by microphones. Each acquired signal is then fully discriminated in terms of acoustic external noise, gel-associated noise and most recently particle discrimination. The detectors are typically operated at ~200

kPa KPA may refer to: * Keele Postgraduate Association, Keele University, UK, formerly Keele Research Association (KRA) * Kensington (Olympia) station, London, England, National Rail station code * Kenya Ports Authority * ''Kiln phosphoric acid'', a ...

and ~280 K. Due to the construction technique, SSDs are almost insensitive to

background radiation Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources. Background radiation originates from a variety of sources ...

, and their sensitivity can be adjusted by controlling the temperature and pressure of each device.

Results

The final phase II analysis was published in Physical Review Letters in 2012. Spin-dependeant cross section limits were set for light WIMPs.

References

The SIMPLE Phase II dark matter search (2014)

Fabrication and response of high concentration SIMPLE superheated droplet detectors with different liquids (2013)

Final Analysis and Results of the Phase II SIMPLE Dark Matter Search (2012)

Reply to Comment on First Results of the Phase II SIMPLE Dark Matter Search (2012)

Comment on First Results of the Phase II SIMPLE Dark Matter Search (2012)

First Results of the Phase II SIMPLE Dark Matter Search (2010)

SIMPLE dark matter search results (2005)

External links

SIMPLE experiment website
{{Dark matter Experiments for dark matter search