The Quest for Dark Matter

Recent experiments have brought for the first time under a strong experimental basis that the total density of the Universe is Wo = 1.02 ± 0.02. We have for the first time a cosmic agreement, namely matter density WM = 0.27 ± 0.04 and dark energy density WL = 0.73 ± 0.04 add up precisely to Wo ! WM + WL. On the other hand ordinary hadronic matter (quarks and leptons) determined by the Big Bang Nucleo-synthesis (BBN) is also firmly set to WBBN = 0.044 ± 0.004. About 100 years after Einstein's birth we know experimentally the identity of less than 5% of what the Universe is made of, the remaining > 95% escaping to us completely. An enormous effort is being made at LHC in order to discover SUSY particles. SUSY is an “almost necessity” of elementary particle physics. The fact that such particles may also account for the observed non baryonic dark matter is either a big coincidence or a big hint. If such SUSY particles indeed exist, they must have been produced abundantly at the time of the Big Bang and should be detectable underground as some form of Cold Dark Matter (CDM). Indeed one of the main hopes of SUSY is to become the key to the CDM problem: this cannot be achieved unless some kind of relic neutral particles exists (WIMP). Therefore the a priori chance of detecting SUSY underground at the LNGS first should not be underestimated. We should also remark that SUSY is only one of the many candidates for WIMP: other kinds of massive relic particles may exist, which may have weak-like interaction properties and therefore detectable underground.