title: Is the unitarity of the quark-mixing CKM matrix violated in neutron beta-decay?
abstract: 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.
authors.affiliation: Physikalisches Institut der Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Abele
authors.forename: M
authors.initials: M
authors.lastname: Astruc Hoffmann
authors.forename: S
authors.initials: S
authors.lastname: Baessler
authors.forename: D
authors.initials: D
authors.lastname: Dubbers
authors.forename: F
authors.initials: F
authors.lastname: Glück
authors.forename: U
authors.initials: U
authors.lastname: Müller
authors.forename: V
authors.initials: V
authors.lastname: Nesvizhevsky
authors.forename: J
authors.initials: J
authors.lastname: Reich
authors.forename: O
authors.initials: O
authors.lastname: Zimmer