CoGeNT: A Search for Low-Mass Dark Matter using p-type Point Contact
  Germanium Detectors
  CoGeNT employs p-type point-contact (PPC) germanium detectors to search for
Weakly Interacting Massive Particles (WIMPs). By virtue of its low energy
threshold and ability to reject surface backgrounds, this type of device allows
an emphasis on low-mass dark matter candidates (wimp mass of about 10 GeV/c2).
We report on the characteristics of the PPC detector presently taking data at
the Soudan Underground Laboratory, elaborating on aspects of shielding, data
acquisition, instrumental stability, data analysis, and background estimation.
A detailed background model is used to investigate the low energy excess of
events previously reported, and to assess the possibility of temporal
modulations in the low-energy event rate. Extensive simulations of all
presently known backgrounds do not provide a viable background explanation for
the excess of low-energy events in the CoGeNT data, or the previously observed
temporal variation in the event rate. Also reported on for the first time is a
determination of the surface (slow pulse rise time) event contamination in the
data as a function of energy. We conclude that the CoGeNT detector technology
is well suited to search for the annual modulation signature expected from dark
matter particle interactions in the region of WIMP mass and coupling favored by
the DAMA/LIBRA results
