Neutrino mass limit from tritium β decay

Abstract

The paper reviews recent experiments on tritium β-spectroscopy searching for the absolute value of the electron neutrino mass m(ν e ). By use of dedicated electrostatic filters with high acceptance and resolution, the uncertainty on the observable m 2 (ν e ) has been pushed down to about 3 eV 2 . The new upper limit of the mass is m(ν e ) < 2 eV at 95% C.L. In view of erroneous and unphysical mass results obtained by some earlier experiments in β-decay, particular attention is paid to systematic effects. The mass limit is discussed in the context of current neutrino research in particle-and astrophysics. A preview is given of the next generation of β-spectroscopy experiments currently under development and construction; they aim at lowering the m 2 (ν e )-uncertainty by another factor of 100, reaching a sensitivity limit m(ν e ) < 0.2 eV.

Global constraints on absolute neutrino masses and their ordering

“…3), well above the extrema in Eq. (14). Such a (relatively high) best-fit value for Σ implies preferred values m ββ around few × 10 −2 eV, as apparent for the IO region allowed at 2σ in the right panel.…”

“…(3) where some sensitivity of cosmological data to mass ordering may be emerging [15]. Bounds on m β , although free from specific assumptions, are an order of magnitude weaker at present [1,14]. In all cases, significant improvements-and possibly a positive detection-may be expected in the next decade of experimental searches [20].…”

“…In particular, three main observables can probe the absolute mass spectrum: (i) the effective neutrino mass m β in β decay; (ii) the effective mass m ββ in neutrinoless double beta (0νββ) decay, if neutrinos are Majorana fermions; and (iii) the total neutrino mass Σ in cosmology; see, e.g., the reviews in [13][14][15][16].…”

Possibility of measuring theCPMajorana phases in0νββdecay

“…The absolute value of the neutrino mass can be determined from a precise measurement of the end-point part of the β-spectrum of the tritium [26] and other β-decay measurements [27]. Cosmological observations allow to infer the sum of the neutrino masses…”

Thresholde−p⟶ nνescattering and the electron neutrino mass

“…The latest results for the limit on the electron neutrino mass have been derived over a decade ago from data collected in two eV-precision experiments: at Troitsk (Russia) [1][2][3][4] (m ν < 2.05 eV at 95% c.l.) and Mainz (Germany) [5,6], [7] (m 2 µ = −0.6 ± 2.2(stat) ± 2.1(syst) eV 2 or m ν < 2.3 eV at 95% c.l.). A new generation experiment, KATRIN, is currently at the commissioning stage, aiming at a sub-eV precision constraint or measurement of the electron neutrino mass [8].…”