A new upper limit of the electron antineutrino rest mass from tritium β-decay

Abstract A new upper limit of the electron antineutrino rest mass has been deduced from the tritium β-decay spectrum. A source of molecular tritium has been investigated with a new solenoid retarding spectrometer. The results are m v e 2 = −39 ± 34 stat ± 15 syst ( eV ) 2 c 4 from which we conclude m v e ≤ 7.2 eV with 95% c.l. Our β-endpoint corresponds to a 3 H 3 He atomic mass difference of Δm( 3 H  3 He ) = 18591 ± 3 eV/c 2 (1σ).