Is the unitarity of the quark-mixing CKM matrix violated in neutron beta-decay?
We report on a new measurement of neutron beta-decay asymmetry. From the result A(0) = -0.1189(7), we derive the ratio of the axial vector to the vector coupling constant lambda = g(A)/g(V) = -1.2739(19). When included in the world average for the neutron lifetime tau = 885.7(7) s, this gives the first element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix V(ud). With this value and the Particle Data Group values for V(us) and V(ub), we find a deviation from the unitarity condition for the first row of the CKM matrix of Delta = 0.0083(28), which is 3.0 times the stated error.
Abele
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H
Physikalisches Institut der Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany.
Astruc Hoffmann
M
M
Baessler
S
S
Dubbers
D
D
Glück
F
F
Müller
U
U
Nesvizhevsky
V
V
Reich
J
J
Zimmer
O
O