©2020 by Rik Bhattacharyya, Texas A&M University, USA.

Dark Matter

Planck have estimated that our Universe comprises  ~ 27 % dark matter, which is only felt by gravitationally, can't be seen while only 5% is the 'visible' matter including all colossal galaxies. Weakly Interacting Massive Particles (WIMPs) is the predilection of the community as dark matter candidates. Cryogenic Dark Matter Search is an experiment aimed to measure the nuclear recoil energy in a WIMP-nucleus elastic scattering.

All evidence indicate that no SM (standard model) particle can be a 'suitable' dark matter candidate (sterile neutrino can be warm dark matter but it's too light to be the only DM candidate, also the hierarchy of large scale structure formation becomes opposite to that of the cold dark matter model). Two SM particle can produce DM particles in colliders lead to 'collider search'. Two DM particles annhilate producing SM particles lead to 'indirect search'. Finally, elastic scattering of one DM and SM particle open the path of 'direct search'. But all of these underlying interactions between SM and DM sectors are still unknown !

CDMS II (2004-08) had total 30 detectors stacked into 6 towers at Soudan Underground Laboratory, USA. The 'grid' lines in the surface were actually 4 phonon sensors in four quadrant whereas the opposite face had 2 charge channels. This detectors were called z-Ionization and Phonon detectors (ZIP). ZIP detectors were operated in low bias voltage (-3/4 V).
In later run, SuperCDMS Soudan (2012-15), iZIPs (interleaved ZIPs) were installed which had 4 phonon channels and 2 charge channels simultaneously (that's why interleaved) in both surfaces.
There were two modes of operations : iZIP mode (4 V)  and CDMSlite mode (70 V). In the next generation SuperCDMS SNOLAB will have  24 detectors and two mode of operations: iZIP (6/8 V) and HV mode (100 V). It will be start around 2020 at Creighton Mine, SNOLAB, Sudbury, Canada !

This is called exclusion plot. Each experiment is tracing out a curve on this DM-nucleon cross-section vs. WIMP mass parameter space. The region above each curve is excluded for DM search with 90 % confidence by that specified experiment. Since, no experiment yet have confirmed the existence of dark matter or WIMPs albeit got possible events or signatures. The yellow region in the lower part is called neutrino floor. Neutrino floor is the measure of the interaction strength for a particular WIMP mass below which it is very hard to distinguish an event from neutrino and DM interactions. We have to cope that in that case. Also, this neutrino floor is also a subject of research for which MINER is going to start.

Go to the following pages, notes, videos to garner a brief idea of dark matter and this challenging field of 'dark' physics. Wait a minute! You've noticed 68% is 'dark energy'. If 25% is so challenging, what's about the rest 68% ?

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