First Direct Determination of the Superallowed β-Decay QEC Value for 14O

We report the first direct measurement of the O-14 superallowed Fermi beta-decay Q(EC) value, the last of the so-called traditional nine superallowed Fermi beta decays to be measured with Penning trap mass spectrometry. O-14, along with the other low-Z superallowed beta emitter, C-10, is crucial for setting limits on the existence of possible scalar currents. The new ground state Q(EC) value, 5144.364(25) keV, when combined with the energy of the 0(+) daughter state, E-x(0(+)) = 2312.798(11) keV [F. Ajzenberg-Selove, Nucl. Phys. A523, 1 (1991)], provides a new determination of the superallowed beta-decay QEC value, Q(EC)(sa) = 2831.566(28) keV, with an order of magnitude improvement in precision, and a similar improvement to the calculated statistical rate function f. This is used to calculate an improved Ft value of 3073.8(2.8) s.