Distinguishing the Oνββ-decay mechanisms

Many new 0νββ-decay experiments are planned or in preparation. If the 0νββ-decay will be detected, the key issue will be what is the dominant mechanism of this process. By measuring only transitions to the ground state one can not distinguish among many of the 0νββ-decay mechanisms (the light and heavy Majorana neutrino exchange mechanisms, the trilinear R-parity breaking mechanisms etc.). We show that if the ratio of the 0νββ-decay half-lifes for transitions to the 0 ⁺ first excited and ground states is determined both theoretically and experimentally, it might be possible to determine, which 0νββ-decay mechanisms is dominant. For that purpose the corresponding nuclear matrix elements have to be evaluated with high reliability. The present work is giving strong motivations for experimental studies of the 0νββ-decay transitions to the first excited 0 ⁺ states of the final nuclei.