B. Bornschein

Final results from phase II of the Mainz neutrino mass searchin tritium \({\beta}\) decay

Abstract.This paper reports on the improved Mainz experiment on tritium

The Mainz neutrino mass experiment

beta

Self-charging of quench condensed tritium films

spectroscopy which yields a 10 times higher signal to background ratio than before. The main experimental effects and systematic uncertainties have been investigated in side experiments, and possible error sources have been eliminated. Extensive data taking took place in the years 1997 to 2001. A residual analysis of the data sets yields for the square of the electron antineutrino mass the final result of

Newest results from the Mainz neutrino mass experiment

m^2(nu_e) = (-0.6 pm 2.2_{mathrm{{stat}}} pm 2.1_{mathrm{{syst}}})

Limits on neutrino masses from tritium β decay

eV2/c4. We derive an upper limit of

Newest results from the Mainz neutrino-mass experiment

m(nu_e)leq 2.3

Results from the mainz neutrino mass experiment

eV/c2 at 95% confidence level for the mass itself.

Results from the Mainz neutrino mass experiment

The Mainz neutrino mass experiment is investigating the endpoint region of the tritium β decay spectrum to determine the mass of the electron antineutrino. For this purpose we have developed a new type of spectrometer with magnetic adiabatic collimation and subsequent e lectrostatic filter (MAC-E filter) [1]. After finishing an extensive improvement programme in 1997 measurements have been resumed in 1998 with a 5 times higher signal rate and a two times lower background rate (≈ 15 mHz). Also the homogeneous thickness of the evaporated T2 source film could be stabilized by cooling it down to temperatures below 2 K. Thereby, previously observed systematic distortions of the spectrum by an uncontrolled energy loss in a dewetted, recrystalized film could be avoided [2,3]. On the other hand, we have discovered and explained a charging of the T2 film up to a critical field strength of 62 MV/m due to the residual daughter ions after β decay [4]. Until end of 2001, 12 runs (Q1 Q12) covering a total measuring time of one year will have been performed with the upgraded apparatus. Results up to Q5 have been published in ref. [5] with the result mν = (3.7 ± 5.3stat ± 2.1sys) eV/c which corresponds to an upper limit for the neutrino mass of mν ≤ 2.8 eV/c 2 (95 % C.l.). In a recent update [6] runs up to Q8 are included in the analysis yielding (preliminarly) mν = (1.6 ± 2.5stat ± 2.1sys) eV/c and mν ≤ 2.2 eV/c (95 % C.l.).

Latest results from the Mainz neutrino mass experiment

Self-charging of a solid tritium film (T2) has been discovered by chance in a precision β spectroscopy experiment on tritium β decay as a shift of the endpoint energy by several eV. The effect was then investigated systematically as a function of film thickness and time by measuring the energy shift of monochromatic conversion electrons from 83mKr evaporated onto T2 films. The steady state is characterized by a practically constant, critical electric field strength Ec≈62 MV/m (≈20 mV/monolayer) over the film, at which the residual positive charges attain sufficient mobility to penetrate the film towards the conducting substrate. This kind of breakthrough behaviour is analyzed in terms of a thermal hopping model, where a trapping potential of Φ0≈175 kBK is lowered in direction of the electric force by a factor of 3 in order to facilitate hopping at a film temperature of about 1.9 K.

KATRIN - a next generation tritium beta decay experiment with sub-eV sensitivity for the electron neutrino mass

The Mainz neutrino-mass experiment investigates the endpoint region of the tritium β-decay spectrum with a MAC-E spectrometer to determine the mass of the electron antineutrino. By the recent upgrade, the former problem of dewetting T2 films has been solved, and the signal-to-background ratio was improved by a factor of 10. The latest measurement leads to (m_nu ^2 = - 3.7 pm 5.3(stat.) pm 2.1(syst.){{eV^2 } mathord{left/ {vphantom {{eV^2 } {c^4 }}} right. kern-nulldelimiterspace} {c^4 }}), from which an upper limit of (m_nu < 2.8{{eV^2 } mathord{left/ {vphantom {{eV^2 } {c^2 }}} right. kern-nulldelimiterspace} {c^2 }}(95% C.L.)) is derived. Some indication for the anomaly, reported by the Troitsk group, was found, but its postulated half-year period is contradicted by our data. To push the sensitivity on the neutrino mass below 1 eV/c2, a new larger MAC-E spectrometer is proposed. Besides its integrating mode, it could run in a new nonintegration operation MAC-E-TOF mode.