[Triumf-seminars] TRIUMF Theory Seminar today at 13:00

[TRIUMF Seminars]

Date/Time: Tue 2019-06-11 at 13:00

Location:  Theory Room         

Speaker:   John Vergados (Ioannina U)

Title:     Dark matter in the cosmos-The Hunt to Find it in the Laboratory

Abstract: There is plenty of evidence at all scales (galaxies, cluster of galaxies, cosmological distances) that most of the energy content of the universe is of unknown nature, i.e, 70% is dark energy and 25% dark matter. Only 5% is made up of matter of known nature, in atoms, in stars, in planets etc,
constituents predicted by the standard model. Thus unraveling the nature of the dominant components and, in particular, of dark matter is one of the most important open problems in science. This nature can only be understood by the direct detection of its constituents in the laboratory. This can be achieved, if there exists a week interaction, much stronger than gravity, between the dark matter and ordinary matter. The constituents are supposed to have a mass and are called WIMPs (weakly interacting massive particles). We have no idea what this mass is, but from the rotational curves we know that the constituents must be non relativistic, regardless of the size of their mass.

The experimental techniques for the direct detection crucially depend on the assumed WIMP mass. Historically the first searches assumed WIMP masses of many GeV and, therefore, heavy nuclear targets were favored. Thus the hunt for DM began and evolved into a multi-pronged and interdisciplinary enterprise, combining cosmology and astrophysics, particle and nuclear physics as
well as detector technology, which will be reviewed. Since the WIMP energy is in the keV region, the nucleus cannot be excited and only the nuclear recoil can be measured. As a result, unfortunately, the signal cannot be easily distinguished from backgrounds. After thirty years of intensive work against formidable backgrounds by a lot of large experimental teams, no dark matter has been found. Impressive limits on the nucleon cross section have, however, been obtained. Extension of these searches to GeV or sub-GeV WIMPs is also been considered using light nuclear targets. 

It may very well be that the WIMPs are much lighter, as suggested by some theories. We will continue our discussion with particles that presumably exist: a) Sterile neutrinos with a mass in the keV region, searched with atomic as as well as nuclear targets. b) axions with masses in mueV-eV region, to be detected by exploiting their conversion to photons in a magnetic field, in resonant cavities (ADMX, CAPP experiments). Also in atomic physics experiments at low temperatures, exploiting spin induced transitions in the presence of suitable magnetic fields.



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