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ft Value of O14 and the Universality of the Fermi Interaction

Bardin, R. K. and Barnes, C. A. and Fowler, W. A. and Seeger, P. A. (1962) ft Value of O14 and the Universality of the Fermi Interaction. Physical Review, 127 (2). pp. 583-596. ISSN 0031-899X. doi:10.1103/PhysRev.127.583.

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The conserved-vector-current theory of the strangeness-conserving weak decays predicts that GV, the vector coupling constant in nuclear beta decay, should be equal to Gμ, the coupling constant in the muon decay. To make possible a more precise comparison of GV and Gμ, the ft value of O14 has been remeasured. The endpoint energy of the positron decay has been determined by measuring the Q values of the reactions C12(He3, n)O14 and C12(He3, p)N14* (2.311-MeV state), using the same techniques and equipment where possible in order to minimize the uncertainty in the difference of the Q values. The results of these measurements are Qn=-1148.8±0.6 keV and Qp=2468.4±1.0 keV, which yield Emax(β+)=1812.6±1.4 keV, all energies relative to the Li7(p, n)Be7 threshold assumed as 1880.7±0.4 keV. The half-life of O14 has also been remeasured as 71.00±0.13 sec, which implies a partial half-life of 71.43±0.15 sec for the transition to the 2.311-MeV state of N14. Averaged with the recent half-life measurement of Hendrie and Gerhart, we obtain an ft value of 3075±10 sec for the O14 decay, after correcting for nuclear form factors, electron screening, and K-capture competition. With the radiative corrections of Kinoshita and Sirlin, the value obtained for GV is (1.4025±0.0022)×10^-49 erg-cm^3, where the quoted error is experimental in origin. This is to be compared with the value computed from recent muon decay measurements, Gμ=(1.4312±0.0011)×10^-49 erg-cm^3, which is (2.0±0.2)% larger. As there appear to be several possible theoretical explanations for this small discrepancy, the present results are consistent with the conserved-vector-current hypothesis.

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Additional Information:©1962 The American Physical Society. Received 13 March 1962. The authors take pleasure in acknowledging their indebtedness to Professor R.F. Christy, Professor R.P. Feynman, Professor M. Gell-Mann, Professor H.A. Weidemüller, and Dr. J.C. pati for many valuable theoretical discussions. Supported in part by the Joint Program of the Office of Naval Research and the U.S. Atomic Energy Commission.
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Deposited On:29 Jul 2008 19:32
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