WIMP (from the English WIMP, Weakly Interacting Massive Particle ) is a hypothetical weakly interacting massive particle . Although there is no established term for this concept in Russian-language literature, the word “WIMP” is widely used in colloquial speech of specialists. Wimps are candidates for the role of the main component of cold dark matter , which makes about a quarter of the contribution to the total density of the Universe (the observed baryon density is 5 times less). It is assumed that of the four fundamental interactions, wimps participate only in the weak and gravitational . Therefore, relict (born shortly after the Big Bang ) wimps are very difficult to detect experimentally. The mass of WIMPs should be at least several tens of times greater than the mass of the proton  . Among the possible candidates for the role of WIMPs, the lightest supersymmetric particles ( neutralino ), which are stable in most theories of supersymmetry, are most often considered.
|Involved in interactions||Gravity  , weak|
|Weight||Must be at least several tens of times the mass of the proton |
|In honor of whom or what is named||Weak interaction , massiveness|
Pilot Detection Attempts
It is assumed that the wimps make up a spherical halo in our galaxy ; they must move randomly , with a Maxwellian velocity distribution (the average speed in the solar region is about 300 km / s ). If the scattering cross section of WIMPs on the atomic nucleus is not too small, they can be directly detected using nuclear detectors that are well protected from the external background (in particular, it is necessary to place the detector deep underground to protect itself from cosmic radiation). Owing to the orbital and diurnal motion of the detector, together with the Earth, the detector count rate will experience annual and diurnal variations; thanks to this, the useful signal can be separated from the background. The maximum counting rate is expected when the projection of the Earth's orbital velocity onto the speed of the Sun relative to the center of the Galaxy (and WIMP gas) is maximum.
The DAMA collaboration claims  that in a long-term experiment with a detector consisting of NaI (Tl) scintillators and located in an underground laboratory of Gran Sasso (Italy), annual variations in the count rate were observed, which are in phase agreement with the expected variations. From the results of this experiment it follows that the WIMPs should have a mass of 30 to 100 GeV / s 2 and the elastic scattering cross section for nuclei is (2-15) ⋅ 10 −6 pbn . Other collaborations in the search for dark matter particles do not confirm the existence of such particles - there is a contradiction that should be resolved by future research (2013).
In December 2009, the CDMS -2 collaboration ( Cryogenic Dark Matter Search ) published a paper reporting the registration of two events in the signal area, which can be interpreted as evidence of WIMP detection with a probability of 77%, based on estimates of expected signals from the background [ 4]  . The probability that these events are explained by background noise  is 23%.
In February 2010, a small CoGeNT experiment reported the registration of several hundred events in 56 days, which is interpreted as a possible signal from WIMPs with a mass of 7-11 GeV / s 2 (while scientists are careful in their conclusions: according to them, the results must be checked) .    The CoGeNT ( Coherent Germanium Neutrino Technology ) detector is a silicon - germanium semiconductor disk the size of a hockey puck and is located in a former iron ore mine in Minnesota at a depth of about 600 meters . Soudan Underground Mine State Park , in the same one as the CDMS detector). [ten]
In June 2011, the results of the CoGeNT experiment were published, interpreted as confirmation of seasonal signal variations similar to those predicted theoretically and previously recorded in the Italian DAMA experiment    .
In September 2011, the results of the second phase of the CRESST experiment using cryogenic detectors consisting of single crystals of calcium tungstate were published  . With an accumulated exposure of 730 kg · days, the authors found 67 events coinciding with the experimental signature of the recoil nuclei. This number exceeds the estimated expected background from external neutrons, gamma rays, etc. If we interpret the signal as a manifestation of WIMP collisions with nuclei, then two possible regions in the parameter space can describe it: one of them concentrates around the WIMP mass M = 11 , 6 GeV / s 2 and elastic scattering cross sections at the core σ = 3.7⋅10 −5 pbn, the second around values M = 25.3 GeV / s 2 and σ = 1.6⋅10 −6 pbn.
In April 2013, the CDMS collaboration, clarifying earlier data from the second phase of its experiment using silicon semiconductor detectors, announced the registration of dark matter particles with a confidence level of three standard deviations , or with a probability of 99.81%. With an expected noise level of 0.7 events, it was possible to register three events with recoil nuclei energies of about 10 keV . The estimated mass of recorded WIMPs is M = 8.6 GeV / s 2   . In this case, as the authors themselves note, there remains a contradiction with the data of the more sensitive XENON experiment, which has not found evidence for the existence of WIMPs with such mass and scattering cross section at nuclei, and two other experiments that see an indication of WIMPs (DAMA and CDMS) observe a signal in other areas of the parameter space that are not compatible with each other or with CDMS data. Therefore, there is no final answer yet whether WIMPs are registered experimentally.
In October 2013, the results of the most sensitive at that time LUX experiment conducted in South Dakota were published. The search was conducted over a wide range of possible WIMP masses with a peak in sensitivity for a mass of 33 GeV / s 2  . For 85 days, the researchers did not find a single signal out of 1,600 expected, thus setting the most stringent restrictions on the possible parameters of WIMPs. This result coincided with the less accurate XENON experiment, but contradicted the results obtained by the CoGENT and CDMS groups   .
There are also suggestions regarding indirect WIMP detection. Most WIMPs fly through the Sun without interacting with its substance, and therefore, they cannot be gravitationally captured. However, if the WIMP is scattered on one of the nuclei inside the Sun, it can reduce the speed and remain in the gravitational field of the Sun. Gradually accumulating in the gravitational potential well , the wimps create a concentration near its center that is sufficient to begin to annihilate with each other. Among the products of such annihilation there may be high-energy neutrinos , freely leaving the center of the Sun. They can be registered with a ground-based detector (for example, Super Kamiokande ). Indirect detection of gravitationally captured WIMPs annihilating in the center of the Earth or in the core of the Galaxy is also possible. Most of these proposals have not yet been implemented.
In October 2010, Dan Hooper of the Fermi National Laboratory and Lisa Goodenough of the University of New York said they were able to identify the annihilation of WIMPs and their antiparticles in one of the galaxies. They analyzed the data on gamma radiation recorded by the Fermi orbital gamma telescope , and concluded that none of the other types of sources can explain the observed facts. According to the estimate given in the work, the mass of WIMPs should be in the range of 7.3–9.2 GeV / s 2    .
- Ryabov V.A., Tsarev V.A., Tskhovrebov A.M. Searches for dark matter particles // UFN . - 2008 .-- T. 178 . - S. 1129-1164 . - DOI : 10.3367 / UFNr.0178.200811a.1129 .
- Roszkowski L., Sessolo EM, Trojanowski S. WIMP dark matter candidates and searches - current status and future prospects // Reports on Progress in Physics. - 2018 .-- Vol. 81. - P. 066201 (43 pp). - DOI : 10.1088 / 1361-6633 / aab913 . - arXiv : 1707.06277 .
- Particle Data Group review article on WIMP search
- On the dark side // STRF.ru - “Science and Technologies of Russia”, 12.12.2013
- The experiments
- amazing world inside the atomic nucleus. Questions after the lecture , LPI, September 11, 2007
- Igor Sokalsky. Dark Matter // Chemistry and Life . - 2006. - No. 11 .
- Geoff Brumfiel. Italian group claims to see dark matter - again (Eng.) // Nature . - 2008. - Vol. 452 . - P. 918 .
- The CDMS II Collaboration. Dark Matter Search Results from the CDMS II Experiment (Eng.) // Science . - 2010. ( full version from arxiv.org )
- Scientists for the first time experimentally recorded particles of dark matter . RIA Novosti (02/12/2010). Date of treatment February 12, 2010. Archived on February 5, 2012.
- Scientific American. Dark Matter Researchers Still in the Dark as Underground Search Returns Uncertain Results, 12/17/2009.
- Physicists have announced the possible registration of light dark matter , Lenta.ru, 03/01/2010.
- CE Aalseth et al. (CoGeNT collaboration), Results from a Search for Light-Mass Dark Matter with a P-type Point Contact Germanium Detector , arXiv: 1002.4703 [astro-ph], 02.25.2010.
- Eric Hand. A CoGeNT result in the hunt for dark matter . Nature News (February 26, 2010). Archived on February 5, 2012. Note: article will only be publicly accessible for a few days
- Scientists have found new evidence for the existence of dark matter // RIA Novosti , 02/27/2010
- CE Aalseth et al. Search for an Annual Modulation in a P-type Point Contact Germanium Dark Matter Detector // arxiv.org . - 2011.
- New Data Still Have Scientists in Dark Over Dark Matter (Eng.) , Science Daily (June 8, 2011). Date of treatment June 8, 2011.
- New evidence has not shed light on the nature of dark matter , Wikinews (June 8, 2011). Date of treatment June 8, 2011.
- G. Angloher et al. Results from 730 kg days of the CRESST-II Dark Matter search (Eng.) // The European Physical Journal C. - 2011. - Vol. 72, no. 4 . - P. 1971. - DOI : 10.1140 / epjc / s10052-012-1971-8 . - arXiv : 1109.0702 .
- CDMS Collaboration. Dark Matter Search Results Using the Silicon Detectors of CDMS II. - 2013 .-- arXiv : 1304.4279 .
- A. Berezin . Declared registration of dark matter particles , Compulent (April 15, 2013). Date of treatment April 17, 2013.
- Paul Preuss . First Results from LUX , Berkeley National Laboratory (30 october 2013). Date of appeal October 31, 2013.
- Adrian Cho . New Experiment Torpedoes Lightweight Dark Matter Particles , Science NOW (Oct. 30, 2013). Date of appeal October 31, 2013.
- Eugenie Samuel Reich . No sign of dark matter in underground experiment , Nature News (30 october 2013). Date of appeal October 31, 2013.
- Physicists “saw” traces of dark matter in data from the Fermi telescope . RIA Novosti (October 23, 2010). Date of treatment October 23, 2010. Archived on February 5, 2012.
- Fermilab theorist sees dark matter evidence in public data . Symmetry Breaking (October 22, 2010). Date of treatment October 23, 2010. Archived on February 5, 2012.
- Dan Hooper, Lisa Goodenough. Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope // arxiv.org . - 2010.