DAMA/NaI results on particle Dark Matter investigation
The annual modulation signature
The annual modulation signature is very distinctive since a seasonal effect
induced by DM particles must simultaneously satisfy all the following
1) the rate must contain a component modulated according to a cosine function;
2) with one year period;
3) a phase that peaks roughly around June 2nd;
4) this modulation must only be found in the low energy range, where DM particles can induce signals;
5) it must apply to those events in which just one detector of many actually "fires" ("single-hit" events), since the probability that DM particles would have multiple interactions is negligible;
6) the modulation amplitude in the region of maximal sensitivity must be less than about 7% for usually adopted halo distributions, but it can be significantly larger in case of some possible scenarios.
Only systematic effects able to fulfil these requirements and to account for the whole observed modulation amplitude could mimic this signature; thus, no other effect investigated so far in the field of rare processes offers a so stringent and unambiguous signature.
With the present technology, the annual modulation signature remains the main signature of a DM particle signal in the galactic halo, offering an efficient model independent signature, able to test a large set of DM candidate particles, of cross sections and of halo densities; it was originally suggested in the middle of '80 by Freese et al..