MiniCLEAN is dark matter detector of the DEAP/CLEAN collaboration located approximately 2km underground in VALE's Creighton mine near Sudbury, Ontario, Canada. It is one in a sequence of liquid argon (LAr) and liquid neon (LNe) detectors, and is the successor of MicroCLEAN, which was operated at Yale. The DEAP/CLEAN collaboration is pursuing a staged approach to dark matter detection, focused on exploiting the unique properties of LAr and LNe as a scintillator. All noble gases scintillate when charged particles pass through them, and when liquified, have a high enough density to make an effective target for the dark matter class of candidates known collectively as Weakly Interacting Massive Particles or WIMPs. In addition, the timing of the scintillation light allow nuclear recoils (the signal of WIMPs) to be separated from electron recoils (caused by natural radioactivity) with extremely high efficiency.
The DEAP/CLEAN focus is on purely liquid detectors, also called "single-phase" detectors, rather than combination liquid+gas detectors, and specifically on Ar and Ne. The simplicity of a liquid-only detector, and the relatively low cost of argon and neon, make it practical and inexpensive to scale the technology up to 50 tonne targets with minimal R&D.
The Berkeley group is highly involved in the construction, testing and commissioning of the detector at SNOLAB. Maintenance activities will continue through detector cooling and data taking.Chris B. Chris J.
Vacuum ultra violet (VUV) light is a very short wavelength radiation in the range of 10nm to 100nm. It comprises an extreme wavelength range outside from the visible spectrum and hence from the detection capabilities of usual photodetectors such as PMTs. Nevertheless, materials known as wavelenght-shifters (WLS) can absorb the energetic VUV photons and reemit an isotropic spectrum of low energy photons above the PMT thresholds, allowing their detection.
Tetraphenyl Butadiene (TPB) is a commonly used WLS in neutrino and dark matter liquid noble gas scintillator detectors. An important parameter characterizing the material is the wavelength shifting efficiency so, a precise measurement of the spectrum for the widest range of wavelengths is a crucial point for future detectors using lighter scintillator elements like Ne or He.Chris B
Measurements of galaxies, clusters, and the cosmic microwave background have revealed that the universe is filled with invisible matter; matter which does not emit, reflect, or absorb light, but can be detected through its gravitational effects. This matter has been dubbed "dark matter," and further study has indicated that it cannot be made from any particle in the Standard Model. Recent exiting results from the Planck telescope have estimated the dark matter content of the universe at 26.8%, and the race is on to detect it in a laboratory environment to learn about its microscopic properties. Does dark matter interact through the weak force? Is it very light or very heavy? What model of particle physics could provide a dark matter candidate and replace the Standard Model?
The WIMP, a theoretical particle that interacts through the weak force and is massive (GeV scale), is a well-motivated dark matter candidate. Cosmologically, the WIMP is favored because if a WIMP exists and is stable, it is naturally produced with the density of dark matter we observe today. This result is known as "the WIMP miracle". In particle physics, specifically in several supersymmetric models, the existence of a WIMP is closely tied to the conservation of a quantum number called R-parity. R-parity can be thought of as a label describing whether a particle is supersymmetric or whether it belongs to the Standard Model. Under R-parity the lightest supersymmetric particle would not be able to decay, and could account for the observed density of dark matter.
The general approach to WIMP detection is to build a very clean detector, low in natural radioactivity, as large as possible, and place it deep underground to shield it from cosmic rays. A WIMP passing though the experiment will sometimes interact with the nucleus of one of the atoms in the detector, depositing energy that can be observed via a variety of technologies. The challenge is to distinguish a WIMP collision from events caused by electrons, neutrons, and gamma rays depositing similar amounts of energy in the detector.
Learn more about MiniCLEAN at the DEAP/CLEAN collaboration website, from which much of the above information was taken.
Or if you'd prefer your information in comic form, see the MiniCLEAN book (by Andy Mastbaum).