DAMA/NaI results on particle Dark Matter investigation
The same data have also been investigated by a Fourier analysis
as shown in the figure on the left, where a clear peak
corresponding to a period of about 1 year is present.
Modulation is not observed above 6 keV (we remind that the experiment has taken data
from single photoelectron to the MeV region despite the optimization has been done for the
lowest energy region). As an example in the figure it can be seen the absence
of any modulation effect in the energy interval 6-14 keV.
A careful quantitative investigation of all the known possible sources of systematic and side reactions has been regularly carried out and published at time of each data release. No systematic effect or side reaction able to account for the observed modulation amplitude and to satisfy all the requirements of the signature has been found; for details see devoted literature.