SIMPLE (Superheated Instrument for Massive ParticLe Experiments) is an experiment search for direct evidence of
dark matter
In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...
. It is located in a 61 m
3 cavern at the 500 level of the
Laboratoire Souterrain à Bas BruitLSBB near
Apt in southern
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
. The experiment is predominantly sensitive to
spin-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, it is an elementary particle which interacts via gravity an ...
(or WIMPs).
SIMPLE is an international collaboration with members from
Portugal
Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...
,
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
, and the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
.
Design
The SIMPLE detector is based on
superheated droplet detectors (SDDs), a suspension of 1–2% superheated liquid C
2ClF
5 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 cooling, heating, or reverse cooling/heating cycles of air conditioning systems and heat pumps, where they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are ...
,
freon, 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 th ...
. Once a
nucleation
In thermodynamics, nucleation is the first step in the formation of either a new Phase (matter), thermodynamic phase or Crystal structure, structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically def ...
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 and ~280
K. Due to the construction technique, SSDs are almost insensitive to
background radiation, 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