The first direct determination of the ground-state–to–ground-state <math><mi>Q</mi></math> values of the <math><msup><mi>β</mi><mo>−</mo></msup></math> decay <math><mrow><mmultiscripts><mi>As</mi><mprescripts/><none/><mn>76</mn></mmultiscripts><mspace width="4pt"/><mo>→</mo><mspace width="4pt"/><mmultiscripts><mi>Se</mi><mprescripts/><none/><mn>76</mn></mmultiscripts></mrow></math> and the electron-capture decay <math><mrow><mmultiscripts><mi>Tb</mi><mprescripts/><none/><mn>155</mn></mmultiscripts><mspace width="4pt"/><mo>→</mo><mspace width="4pt"/><mmultiscripts><mi>Gd</mi><mprescripts/><none/><mn>155</mn></mmultiscripts></mrow></math> was performed utilizing the double Penning trap mass spectrometer JYFLTRAP. By measuring the atomic mass difference of the decay pairs via the phase-imaging ion-cyclotron-resonance technique, the <math><mi>Q</mi></math> values of <math><mrow><mmultiscripts><mi>As</mi><mprescripts/><none/><mn>76</mn></mmultiscripts><mspace width="4pt"/><mo>→</mo><mspace width="4pt"/><mmultiscripts><mi>Se</mi><mprescripts/><none/><mn>76</mn></mmultiscripts></mrow></math> and <math><mrow><mmultiscripts><mi>Tb</mi><mprescripts/><none/><mn>155</mn></mmultiscripts><mspace width="4pt"/><mo>→</mo><mspace width="4pt"/><mmultiscripts><mi>Gd</mi><mprescripts/><none/><mn>155</mn></mmultiscripts></mrow></math> were determined to be 2959.265(74) keV and 814.94(18) keV, respectively. The precision was increased relative to earlier measurements by factors of 12 and 57, respectively. The new <math><mi>Q</mi></math> values are 1.33 keV and 5 keV lower compared to the values adopted in the most recent Atomic Mass Evaluation 2020. With the newly determined ground-state–to–ground-state <math><mi>Q</mi></math> values combined with the excitation energy from <math><mi>γ</mi></math>-ray spectroscopy, the <math><mi>Q</mi></math> values for ground-state–to–excited-state transitions <math><mmultiscripts><mi>As</mi><mprescripts/><none/><mn>76</mn></mmultiscripts></math> (ground state) <math><mrow><mo>→</mo><mspace width="4pt"/><mmultiscripts><mi>Se</mi><none/><mo>*</mo><mprescripts/><none/><mn>76</mn></mmultiscripts></mrow></math> (2968.4(7) keV) and <math><mmultiscripts><mi>Tb</mi><mprescripts/><none/><mn>155</mn></mmultiscripts></math> (ground state) <math><mrow><mo>→</mo><mspace width="4pt"/><mmultiscripts><mi>Gd</mi><none/><mo>*</mo><mprescripts/><none/><mn>155</mn></mmultiscripts></mrow></math> (815.731(3) keV) were derived to be <math><mrow><mo>−</mo><mn>9.13</mn><mo>(</mo><mn>70</mn><mo>)</mo></mrow></math> keV and <math><mrow><mo>−</mo><mn>0.79</mn><mo>(</mo><mn>18</mn><mo>)</mo></mrow></math> keV. Thus we have confirmed that both of the <math><msup><mi>β</mi><mo>−</mo></msup></math>-decay and EC-decay candidate transitions are energetically forbidden at a level of at least <math><mrow><mn>4</mn><mi>σ</mi></mrow></math>, thus definitely excluding these two cases from the list of potential candidates for the search of low-<math><mi>Q</mi></math>-value <math><msup><mi>β</mi><mo>−</mo></msup></math> or EC decays to determine the electron-(anti)neutrino mass.Read less <