Münster 2002 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 50: Plenary Session

HK 50.2: Plenary Talk

Friday, March 15, 2002, 11:30–12:00, Plenarsaal

Neutron beta decay and the CKM matrix — •Oliver Zimmer — TU München, Physik Department E18, 85748 Garching

In the standard model of electroweak interactions, the quark mass eigenstates are linked to the weak eigenstates via the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix. Traditionally, the first element of this matrix, V_ud, is determined from well-selected, pure Fermi nuclear beta decays. An alternative derivation, which is free from corrections due to nuclear structure, employs neutron beta decay data. Thereby comparable accuracy has recently been attained, combining the values of the neutron lifetime and of the neutron beta-asymmetry. Results of most accurate determinations of V_ud from both methods, including values of V_us and V_ub from high-energy physics, are in contradiction to the unitarity of the CKM matrix. The origin of the discrepancy is still unresolved. A survey of the field is given, emphasizing recent and ongoing developments in neutron decay experimentation.