A bolometric measurement of the antineutrino mass

TL;DR

This study performs high-precision calorimetric measurements of the beta decay spectrum of 187Re to set new limits on the electron antineutrino mass, achieving the most accurate values to date.

Contribution

It introduces a modified experimental setup with reduced background, enabling more sensitive measurements of the antineutrino mass using silver perrhenate microbolometers.

Findings

End-point energy measured at 2466.1 eV with high precision.

Half-life of 187Re decay determined as 43.2 Gy.

Upper limit for antineutrino mass set at 21.7 eV.

Abstract

High statistics calorimetric measurements of the beta spectrum of 187Re are being performed with arrays of silver perrhenate crystals operated at low temperature. After a modification of the experimental set-up, which allowed to substantially reduce the background of spurious counts and therefore to increase the sensitivity on the electron antineutrino mass, a new measurement with 10 silver perrhenate microbolometers is running since July 2002. The crystals have masses between 250 and 350 micrograms and their average FWHM energy resolution, constantly monitored by means of fluorescence X-rays, is of 28.3 eV at the beta end-point. The Kurie plot collected during 4485 hours x mg effective running time has an end-point energy of 2466.1 +/- 0.8{stat} +/- 1.5 {syst} eV, while the half lifetime of the decay is found to be 43.2 +/- 0.2{stat} +/- 0.1{syst} Gy. These values are the most precise obtained so far for 187Re. From the fit of the Kurie plot we can deduce a value for the squared electron antineutrino mass m(nu)^2 of 147 +/- 237{stat} +/- 90{syst} eV^2. The corresponding 90% C.L. upper limit for m(nu) is 21.7 eV.