First direct neutrino-mass measurement with sub-eV sensitivity

TL;DR

The KATRIN experiment achieved the first direct neutrino-mass measurement with sub-eV sensitivity, improving constraints on the effective electron anti-neutrino mass through high-precision tritium beta-decay spectrum analysis.

Contribution

This work reports the second measurement campaign of KATRIN, increasing source activity and reducing background, leading to the first sub-eV sensitivity in direct neutrino-mass measurement.

Findings

Sensitivity of 0.7 eV/c^2 at 90% CL

Upper limit on neutrino mass < 0.9 eV/c^2

Combined data yields upper limit < 0.8 eV/c^2

Abstract

We report the results of the second measurement campaign of the Karlsruhe Tritium Neutrino (KATRIN) experiment. KATRIN probes the effective electron anti-neutrino mass, $m_{\nu}$, via a high-precision measurement of the tritium $\beta$-decay spectrum close to its endpoint at $18.6\,\mathrm{keV}$. In the second physics run presented here, the source activity was increased by a factor of 3.8 and the background was reduced by $25\,\%$ with respect to the first campaign. A sensitivity on $m_{\nu}$ of $0.7\,\mathrm{eV/c^2}$ at $90\,\%$ confidence level (CL) was reached. This is the first sub-eV sensitivity from a direct neutrino-mass experiment. The best fit to the spectral data yields $m_{\nu}^2 = (0.26\pm0.34)\,\mathrm{eV^4/c^4}$, resulting in an upper limit of $m_{\nu}<0.9\,\mathrm{eV/c^2}$ ($90\,\%$ CL). By combining this result with the first neutrino mass campaign, we find an upper limit of $m_{\nu}<0.8\,\mathrm{eV/c^2}$ ($90\,\%$ CL).