ON THE ELUSIVENESS OF BETA-BETA-0-NU DECAY

To date, no evidence of beta beta 0 nu decay has been found despite tr emendous experimental efforts. In contrast, beta beta 2 nu decay has b een clearly and definitely observed in several nuclei. These experimen tal facts question the reality of beta beta 0 nu decay. This beta beta 0 nu decay which violates lepton number conservation can only occur i f the neutrino is massive and is its own antiparticle or in other word s is a truly neutral particle. The observation of this decay implies t hen that the neutrino is a truly neutral particle and it has a non-zer o mass. But the absence of beta beta 0 nu decay implies only that at l east one of the two necessary conditions is not fulfilled. Since the t ruly neutral character of neutrino is a necessary condition, it is imp ortant to provide objective criteria of truly neutral particles. We pr opose a generalized Gell-Mann and Nishijima formula which provides nat urally the criteria of truly neutral particles. According to these cri teria n and nu are different from their antiparticles for symmetric re ason. The absence of beta beta 0 nu decay could then be simply underst ood. Indeed a truly neutral particle could be more generally defined a s a neutral particle with respect to all charges and is its own antipa rticle. The Dirac character of the neutrino does not contradict any ex perimental fact.