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The neutrinoless double beta(Ovββ)decay is a hypothetical weak process which manifests itself in the“low-energy”environ-ment of atomic nuclei as two neutrons in a parent nucleus(A,Z)decays into two protons in a daughter nucleus(A,Z+2)with the emission of two electrons but no(anti)neutrinos[1].This process violates lepton number-an accidental global symmetry in the Standard Model of particle physics.Its observation would have important implications in the theories those are trying to explain the asymmetry between matter and anti-matter in the Universe.Besides,it would confirm the Majorana nature of neutrinos and provide one of the most promising ways to determine their abso-lute mass scale.Therefore,the search for Ovββ decay has become a priority in nuclear and particle physics.