Dark Matter Search with the Nuclear Isomer Ta-180m
  There is compelling cosmological and astrophysical evidence of dark matter
comprising 27% of the energy budget of the Universe. However, dark matter has
never been observed in direct detection experiments. The long-time favorite
model of Weakly Interacting Massive Particles saw a large experimental effort
with steady progress over recent decades. Since also these large-scale searches
remain unsuccessful to date, it is compelling to look at more exotic dark
matter models which can be constrained with new approaches and much less
scientific resources. Using nuclear isomers is one of these approaches.
$^{180m}$Ta is the rarest known isotope with the longest-lived meta-stable
state whose partial half-life limits are on the order of 10$^{14}$-10$^{16}$
yr. We investigate how strongly interacting dark matter and inelastic dark dark
matter collides with $^{180m}$Ta, leading to its de-excitation. The energy
stored in the meta-stable state is released in the transition, which becomes
the signature for thermalized dark matter in a well-shielded underground
experiment. We report on a direct detection experiment searching for these
dark-matter-induced decay signatures which has further constrained the open
parameter space. We also propose an indirect geochemical experiment to search
for decay products of $^{180m}$Ta in tantalum minerals accumulated over 1
billion years.
