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Abstract

In the near future, the neutrinoless double-beta (0 nu beta beta) decay
experiments will hopefully reach the sensitivity of a few meV to the
effective neutrino mass |m(beta beta)|. In this paper, we tentatively
examine the sensitivity of future 0 nu beta beta -decay experiments to
neutrino masses and Majorana CP phases by following the Bayesian
statistical approach. Provided experimental setups corresponding to the
experimental sensitivity of |m(beta beta)| similar or equal to 1 meV,
the null observation of 0 nu beta beta decays in the case of normal
neutrino mass ordering leads to a very competitive bound on the lightest
neutrino mass m(1). Namely, the 95% credible interval in the Bayesian
approach turns out to be 1.6 meV less than or similar to m(1) less than
or similar to 7.3 meV or 0.3 meV less than or similar to m(1) less than
or similar to 5.6 meV when the uniform prior on m(1)/eV or on
log(10)(m(1)/eV) is adopted. Moreover, one of two Majorana CP phases is
strictly constrained, i.e., 140 degrees less than or similar to rho less
than or similar to 220 degrees for both scenarios of prior distributions
of m(1). In contrast, if a relatively worse experimental sensitivity of
|m(beta beta)| similar or equal to 10 meV is assumed, the constraint on
the lightest neutrino mass becomes accordingly 0.6 meV less than or
similar to m(1) less than or similar to 26 meV or 0 less than or similar
to m(1) less than or similar to 6.1 meV, while two Majorana CP phases
will be essentially unconstrained. In the same statistical framework,
the prospects for the determination of neutrino mass ordering and the
discrimination between Majorana and Dirac nature of massive neutrinos in
the 0 nu beta beta -decay experiments are also discussed. Given the
experimental sensitivity of |m(beta beta)| similar or equal to 10 meV
(or 1 meV), the strength of evidence to exclude the Majorana nature
under the null observation of 0 nu beta beta decays is found to be
inconclusive (or strong), no matter which of two priors on m(1) is
taken.