One of the key ingredients needed to extract quantitative information on neutrino absolute mass scale from the possible measurement of the neutrinoless double-beta (0νββ) decay half-lives is the nuclear matrix element (NME) characterizing such transitions. NMEs are not physical observables and can only be deduced by theoretical calculations. However, since the atomic nuclei involved in the decay are many-body systems, only approximated values are available to date. In addition, the value of the coupling constants to be used for the weak interaction vertices is still an open question, which introduces a further indetermination in the calculations of NMEs. Several experimental approaches were developed in the years with the aim of providing useful information to further constrain the theory. Here we give an overview of the role of charge exchange reactions in this scenario, focusing on second-order processes, namely the double charge exchange (DCE) reactions.

中文翻译：

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对与双Beta衰变有关的二阶同位旋探针的核反应

从可能的无中微子双β（0νββ）衰变半衰期的可能测量中提取中微子绝对质量规模的定量信息所需的关键成分之一是表征这种转变的核基质元素（NME）。NME不是物理可观察到的，只能通过理论计算得出。但是，由于参与衰变的原子核是多体系统，因此迄今为止只有近似值可用。此外，用于弱相互作用顶点的耦合常数的值仍然是一个悬而未决的问题，这在NME的计算中引入了进一步的不确定性。这些年来，人们开发了几种实验方法，旨在提供有用的信息以进一步约束该理论。