Particle Physics Seminar

Matter constitutes 30% of the energy content of the Universe. The remaining 70% is
what is called dark energy, which exhibits unusual repulsive gravitational interactions.
On the matter sheet, only 5% is of known nature, i.e. matter such as found in atoms, in
stars, in planets etc. From observations on all astrophysical and cosmological scales we
know that most of it, i.e. 25%, is dark matter (DM) of unknown nature. The nature of DM
is one of the most important open problems in science. The ongoing hunt for DM is
multi-pronged and interdisciplinary involving cosmology and astrophysics, particle and
nuclear physics as well as detector technology.
In this talk we will focus on the direct detection of the dark matter constituents, the so
called weakly interacting massive particles (WIMPs), in underground labs. The detection
consists of measuring the energy deposited in the detector by the recoiling nucleus, after
its elastic collision with a WIMP (spin independent or spin induced). In obtaining the
event rates one needs models about the WIMP interaction and density in our vicinity as
well as its velocity distribution. No events have so far been observed, only exclusion
plots on the nucleon cross sections have been obtained, which will be discussed. Since
the expected rates are very small and the usual experimental signature is not different
from that of the backgrounds, we will discuss some special signatures that might aid in
the analysis of the experiments such as the time dependence of the signal (modulation
effect) and the option of inelastic scattering, possible in some special targets, by
detecting γ-rays following the de-excitation of the nucleus.