Challenges in Double Beta Decay

Abstract

After nearly 80 years since the first guess on its existence, neutrino still escapes our insight: the mass and the true nature (Majorana or Dirac) of this particle is still unknown. In the past ten years, neutrino oscillation experiments have finally provided the incontrovertible evidence that neutrinos mix and have finite masses. These results represent the strongest demonstration that the Standard Model of electroweak interactions is incomplete and that new Physics beyond it must exist. None of these experimental efforts could however shade light on some of the basic features of neutrinos. Indeed, absolute scale and ordering of the masses of the three generations as well as charge conjugation and lepton number conservation properties are still unknown. In this scenario, a unique role is played by the Neutrinoless Double Beta Decay searches: these experiments can probe lepton number conservation, investigate the Dirac/Majorana nature of the neutrinos and their absolute mass scale (hierarchy problem) with unprecedented sensitivity. Today Neutrinoless Double Beta Decay faces a new era where large scale experiments with a sensitivity approaching the so-called degenerate-hierarchy region are nearly ready to start and where the challenge for the next future is the construction of detectors characterized by a tonne-scale size and an incredibly low background, to fully probe the invertedhierarchy region. A number of new proposed projects took up this challenge. These are based either on large expansions of the present experiments or on new ideas to improve the technical performance and/or reduce the background contributions. On the other hand, nuclear theorists are making remarkable progress in the calculation of the double beta decay nuclear matrix elements in order to eliminate the theoretical uncertainties affecting the particle physics interpretation of this process. In this paper, a review of the most relevant ongoing experiments is given. The most relevant parameters contributing to the experimental sensitivity are discussed and a critical comparison of the future projects is proposed.

Global constraints on absolute neutrino masses and their ordering

“…(5), G is the (calculable) phase space and M is the nuclear matrix element (NME) for a candidate nucleus [15,[50][51][52]. A worldwide search is underway to find possible 0νββ decay signatures in a variety of nuclei, and lower limits on the corresponding half lives have been placed [53][54][55]. Transforming lower bounds on T into upper bounds on m ββ requires theoretical input on the NME and their uncertainties [15,[50][51][52][56][57][58].…”

“…9 (dominated by cosmology). There are good prospects to further probe this region -and possibly go below it-with upcoming or planned 0νββ experiments [53][54][55]. However, unlike Σ, there is no finite lower bound on m ββ , since the null value cannot be excluded a priori for unfavorable Majorana phases (see [102] and refs.…”

Estimation of low energy neutron flux (En⩽ 15 MeV) in India-based Neutrino Observatory cavern using Monte Carlo techniques

“…Neutrons are known to be an important source of background for experiments like direct dark matter searches [1], double beta decay experiments [2], solar neutrino measurements [3], etc. In underground laboratories, neutrons originate from the spontaneous fission of U and Th trace elements in the surrounding rock and the (α, n) interactions on the low Z elements present in the rock.…”

Search for 2βdecay of116Cd with the help of enriched116CdWO4crystal scintillators

“…The observation of the 0ν2β decay will testify the lepton number non-conservation, the Majorana nature of the neutrino, an absolute value and hierarchy of the neutrino masses. The 0ν2β decay is also sensitive to an existence of the right-handed currents, hypothetical particles (majorons) and other effects beyond the SM (see the recent reviews [4][5][6][7][8][9] and references therein).…”