Editing Weakly interacting massive particle (section)

=== Experimental techniques ===

'''Cryogenic crystal detectors''' – A technique used by the [[Cryogenic Dark Matter Search]] (CDMS) detector at the [[Soudan Mine]] relies on multiple very cold germanium and silicon crystals. The crystals (each about the size of a hockey puck) are cooled to about 50 [[Kelvin|mK]]. A layer of metal (aluminium and tungsten) at the surfaces is used to detect a WIMP passing through the crystal. This design hopes to detect vibrations in the crystal matrix generated by an atom being "kicked" by a WIMP. The tungsten [[transition edge sensors]] (TES) are held at the critical temperature so they are in the [[superconducting]] state. Large crystal vibrations will generate heat in the metal and are detectable because of a change in [[electrical resistance|resistance]]. [[Cryogenic Rare Event Search with Superconducting Thermometers|CRESST]], [[CoGeNT]], and [[EDELWEISS]] run similar setups.

'''Noble gas scintillators''' – Another way of detecting atoms "knocked about" by a WIMP is to use [[scintillator|scintillating]] material, so that light pulses are generated by the moving atom and detected, often with PMTs. Experiments such as [[DEAP]] at [[SNOLAB]] and [[DarkSide (dark matter experiment)|DarkSide]] at the [[Laboratori Nazionali del Gran Sasso|LNGS]] instrument a very large target mass of liquid argon for sensitive WIMP searches. [[ZEPLIN]], and [[XENON Dark Matter Search Experiment|XENON]] used xenon to exclude WIMPs at higher sensitivity, with the most stringent limits to date provided by the XENON1T detector, utilizing 3.5 tons of liquid xenon.<ref>{{cite journal |arxiv=1705.06655 |last1=Aprile|first1=E|display-authors=etal  |title=First Dark Matter Search Results from the XENON1T Experiment |journal=Physical Review Letters|volume=119|issue=18|pages=181301|year=2017|doi=10.1103/PhysRevLett.119.181301|pmid=29219593|bibcode=2017PhRvL.119r1301A|s2cid=45532100}}</ref> Even larger multi-ton liquid xenon detectors have been approved for construction from the [[XENON]], [[LUX-ZEPLIN]] and [[PandaX]] collaborations.

'''Crystal scintillators''' – Instead of a liquid noble gas, an in principle simpler approach is the use of a scintillating crystal such as NaI(Tl). This approach is taken by [[DAMA/LIBRA]], an experiment that observed an annular modulation of the signal consistent with WIMP detection (see ''{{section link||Recent limits}}''). Several experiments are attempting to replicate those results, including [[ANAIS]], [[Cryogenic_Observatory_for_Signatures_Seen_in_Next-Generation_Underground_Searches|COSINUS]] and [[DM-Ice]], which is codeploying NaI crystals with the [[IceCube Neutrino Observatory|IceCube]] detector at the South Pole. [[Korea Invisible Mass Search|KIMS]] is approaching the same problem using CsI(Tl) as a scintillator.

'''Bubble chambers''' – The [[PICASSO]] (Project In Canada to Search for Supersymmetric Objects) experiment is a direct dark matter search experiment that is located at [[SNOLAB]] in Canada. It uses bubble detectors with [[Freon]] as the active mass. PICASSO is predominantly sensitive to spin-dependent interactions of WIMPs with the fluorine atoms in the Freon. COUPP, a similar experiment using trifluoroiodomethane(CF<sub>3</sub>I), published limits for mass above 20&nbsp;GeV/''c''<sup>2</sup> in 2011.<ref>{{cite journal |last1=Behnke |first1=E. |last2=Behnke |first2=J. |last3=Brice |first3=S. J. |last4=Broemmelsiek |first4=D. |last5=Collar |first5=J. I. |last6=Cooper |first6=P. S. |last7=Crisler |first7=M. |last8=Dahl |first8=C. E. |last9=Fustin |first9=D. |last10=Hall |first10=J. |last11=Hinnefeld |first11=J. H. |last12=Hu |first12=M. |last13=Levine |first13=I. |last14=Ramberg |first14=E. |last15=Shepherd |first15=T. |last16=Sonnenschein |first16=A. |last17=Szydagis |first17=M. |title=Improved Limits on Spin-Dependent WIMP-Proton Interactions from a Two Liter Bubble Chamber |journal=Physical Review Letters |date=10 January 2011 |volume=106 |issue=2 |doi=10.1103/PhysRevLett.106.021303 |arxiv=1008.3518 |bibcode=2011PhRvL.106b1303B |pmid=21405218 |page=021303|s2cid=20188890 }}</ref> The two experiments merged into PICO collaboration in 2012.

A bubble detector is a radiation sensitive device that uses small droplets of superheated liquid that are suspended in a gel matrix.<ref>{{cite web |url=http://www.bubbletech.ca/radiation_detectors_files/bubble_detectors.html |title=Bubble Technology Industries |access-date=2010-03-16 |archive-date=2008-03-20 |archive-url=https://web.archive.org/web/20080320061130/http://www.bubbletech.ca/radiation_detectors_files/bubble_detectors.html |url-status=dead }}</ref> It uses the principle of a [[bubble chamber]] but, since only the small droplets can undergo a [[phase transition]] at a time, the detector can stay active for much longer periods.{{clarify |reason=this would make more sense if it read 'only a small number of droplets' |date=March 2015}} When enough energy is deposited in a droplet by ionizing radiation, the superheated droplet becomes a gas bubble. The bubble development is accompanied by an acoustic shock wave that is picked up by piezo-electric sensors. The main advantage of the bubble detector technique is that the detector is almost insensitive to background radiation. The detector sensitivity can be adjusted by changing the temperature, typically operated between 15&nbsp;°C and 55&nbsp;°C. There is another similar experiment using this technique in Europe called SIMPLE.

PICASSO reports results (November 2009) for spin-dependent WIMP interactions on <sup>19</sup>F, for masses of 24 Gev new stringent limits have been obtained on the spin-dependent cross section of 13.9 pb (90% CL). The obtained limits restrict recent interpretations of the DAMA/LIBRA annual modulation effect in terms of spin dependent interactions.<ref>{{cite journal |author=PICASSO Collaboration |title=Dark Matter Spin-Dependent Limits for WIMP Interactions on <sup>19</sup>F by PICASSO |journal=Physics Letters B |date=2009 |doi=10.1016/j.physletb.2009.11.019 |bibcode=2009PhLB..682..185A |volume=682 |issue=2 |pages=185–192 |arxiv=0907.0307|s2cid=15163629 }}</ref>

PICO is an expansion of the concept planned in 2015.<ref>{{cite journal |title=Overview of non-liquid noble direct detection dark matter experiments |date=28 October 2014 |journal=Physics of the Dark Universe |doi=10.1016/j.dark.2014.10.005 |arxiv=1410.4960 |bibcode=2014PDU.....4...92C |volume=4 |pages=92–97|last1=Cooley |first1=J. |s2cid=118724305 }}</ref>

'''Other types of detectors''' – [[Time projection chamber]]s (TPCs) filled with low pressure gases are being studied for WIMP detection. The [[Directional Recoil Identification From Tracks]] (DRIFT) collaboration is attempting to utilize the predicted directionality of the WIMP signal. DRIFT uses a [[carbon disulfide]] target, that allows WIMP recoils to travel several millimetres, leaving a track of charged particles. This charged track is drifted to an [[MWPC]] readout plane that allows it to be reconstructed in three dimensions and determine the origin direction. DMTPC is a similar experiment with CF<sub>4</sub> gas.

The DAMIC (DArk Matter In CCDs) and SENSEI (Sub Electron Noise Skipper CCD Experimental Instrument) collaborations employ the use of scientific [[Charge-coupled device|Charge Coupled Devices]] (CCDs) to detect light Dark Matter. The CCDs act as both the detector target and the readout instrumentation. WIMP interactions with the bulk of the CCD can induce the creation of electron-hole pairs, which are then collected and readout by the CCDs. In order to decrease the noise and achieve detection of single electrons, the experiments make use of a type of CCD known as the Skipper CCD, which allows for averaging over repeated measurements of the same collected charge.<ref>{{cite journal|last1=DAMIC Collaboration|last2=Aguilar-Arevalo|first2=A.|last3=Amidei|first3=D.|last4=Baxter|first4=D.|last5=Cancelo|first5=G.|last6=Cervantes Vergara|first6=B. A.|last7=Chavarria|first7=A. E.|last8=Darragh-Ford|first8=E.|last9=de Mello Neto|first9=J. R. T.|last10=D’Olivo|first10=J. C.|last11=Estrada|first11=J.|date=2019-10-31|title=Constraints on Light Dark Matter Particles Interacting with Electrons from DAMIC at SNOLAB|url=https://link.aps.org/doi/10.1103/PhysRevLett.123.181802|journal=Physical Review Letters|volume=123|issue=18|pages=181802|doi=10.1103/PhysRevLett.123.181802|pmid=31763884|arxiv=1907.12628|bibcode=2019PhRvL.123r1802A|s2cid=198985735}}</ref><ref>{{cite journal|last1=Abramoff|first1=Orr|last2=Barak|first2=Liron|last3=Bloch|first3=Itay M.|last4=Chaplinsky|first4=Luke|last5=Crisler|first5=Michael|last6=Dawa|last7=Drlica-Wagner|first7=Alex|last8=Essig|first8=Rouven|last9=Estrada|first9=Juan|last10=Etzion|first10=Erez|last11=Fernandez|first11=Guillermo|date=2019-04-24|title=SENSEI: Direct-Detection Constraints on Sub-GeV Dark Matter from a Shallow Underground Run Using a Prototype Skipper-CCD|journal=Physical Review Letters|volume=122|issue=16|pages=161801|doi=10.1103/PhysRevLett.122.161801|pmid=31075006|issn=0031-9007|arxiv=1901.10478|bibcode=2019PhRvL.122p1801A|s2cid=119219165}}</ref>