Tentative sensitivity of future 0νββ-decay experiments to neutrino masses and Majorana CP phases

Abstract

In the near future, the neutrinoless double-beta (0νββ) decay experiments will hopefully reach the sensitivity of a few meV to the effective neutrino mass |mββ|. In this paper, we tentatively examine the sensitivity of future 0νββ-decay experiments to neutrino masses and Majorana CP phases by following the Bayesian statistical approach. Provided experimental setups corresponding to the experimental sensitivity of |mββ| ≃ 1 meV, the null observation of 0νββ decays in the case of normal neutrino mass ordering leads to a very competitive bound on the lightest neutrino mass m1. Namely, the 95% credible interval in the Bayesian approach turns out to be 1.6 meV ≲ m1 ≲ 7.3 meV or 0.3 meV ≲ m1 ≲ 5.6 meV when the uniform prior on m1/eV or on log10(m1/eV) is adopted. Moreover, one of two Majorana CP phases is strictly constrained, i.e., 140° ≲ ρ ≲ 220° for both scenarios of prior distributions of m1. In contrast, if a relatively worse experimental sensitivity of |mββ| ≃ 10 meV is assumed, the constraint on the lightest neutrino mass becomes accordingly 0.6 meV ≲ m1 ≲ 26 meV or 0 ≲ m1 ≲ 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 0νββ-decay experiments are also discussed. Given the experimental sensitivity of |mββ| ≃ 10 meV (or 1 meV), the strength of evidence to exclude the Majorana nature under the null observation of 0νββ decays is found to be inconclusive (or strong), no matter which of two priors on m1 is taken.

Inference of neutrino nature and Majorana CP phases from $$\mathbf{0}{\nu \beta \beta }$$ decays with inverted mass ordering

“…In contrast, previous works were mainly built on the Bayesian approach [15,16,19,20,24,25,53,56], which, how-ever, severely relies on the unknown priors of model parameters. The prior of a parameter in Bayesian statistics should be assigned according to its physical origin.…”

“…As the overall CP phase of m ee is non-physical, it is a convenient choice to assign two Majorana CP phases to the lightest and the heaviest neutrino states [9][10][11], such that only one phase parameter will survive when the lightest neutrino mass is vanishing. The importance of 0νββ decay searches for neutrino physics is well recognized [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], as it can answer: (i) the nature of neutrinos, (ii) the Majorana CP phases, (iii) the absolute scale of neutrino masses, and (iv) the neutrino mass ordering. While the neutrino masses can be better probed by other observations (e.g., cosmology and oscillation experiments), the 0νββ decay search seems to be the only reliable way towards the neutrino nature and the Majorana CP phases.…”

“…In the assumption of NO, a meV sensitivity to |m ee | is required to extract possible information of Majorana CP phases [14,18,19,[22][23][24][25], which is, however, far beyond the capability of the next-generation experiments in the near future. One would wish that IO is true from a practical point of view, as the full parameter space of IO will be covered with a 10 meV sensitivity in the not-too-distant future.…”

Neutrino meets ultralight dark matter: $\boldsymbol{0νββ}$ decay and cosmology

“…The constraint from 0νββ-decay searches (KamLAND-Zen [68]) is shown as the solid cyan line. The projection with an ultimate sensitivity goal of 0νββ-decay experiments |m ee | = 1 meV [78][79][80][81] is shown as the dotted cyan line. In order to translate results into the m φ -g plane, we have used Eq.…”

Beyond-mean-field approaches for nuclear neutrinoless double beta decay in the standard mechanism

“…Next-generation experiments [49,388] aiming to increase detector mass further to tonne-scale size and to reduce backgrounds as much as possible, are expected to reach a discovery potential of half-life 10 28 years after a few years of running, providing a definite answer on the mass hierarchy of neutrinos based on our current knowledge on the NME of 0νββ decay [116]. If the neutrino mass spectra follow the norm-ordering unfortunately, we need to build a detector with the effective-neutrino-mass sensitivity down to | m ββ | 1 meV [389,390,391,392,393,394,395] and the half-life sensitivity up to 10 30 years, which will be a real challenge.…”