The DAMA project: Achievements, implications and perspectives

Experimental observations and theoretical arguments at galactic and larger scales pointed out that a large fraction of the Universe is composed of Dark Matter (DM) particles. This has motivated the pioneer DAMA experimental efforts to investigate the presence of such particles in the galactic halo, by exploiting a model independent signature and very highly radio-pure apparatus in deep underground. In this paper, after a short introductory part, the long-standing model-independent annual modulation effect measured by DAMA Collaboration, with various experimental configurations, is examined. In the energy region between 2 and 6 keV, the data from DAMA/NaI, DAMA/LIBRA-phase1 and DAMA/LIBRA-phase2 (full exposure: 2.46 ton yr) confirm the evidence of a signal that meets all the several specific requirements of the exploited model independent DM annual modulation signature, at 12.9 C.L. The DAMA/LIBRA-phase2 configuration, profiting from new high quantum efficiency photomultipliers, new electronics and other improvements with respect to DAMA/LIBRA-phase1, has also allowed the confirmation of such an evidence down to a software energy threshold of 1 keV. The complexity and the uncertainties of corollary model dependent quests for the DM candidate particle(s) and related scenarios are also addressed at some extent and several of the many possibilities are examined. The efforts towards the new phase3 of the experiment are summarized, showing the strategies and the results obtained with the present developments.