The European Physical Journal C - Particles and Fields

, Volume 33, Issue 1, pp 1–8

Quark mixing, CKM unitarity

The unitarity problem


  • H. Abele
    • Physikalisches Institut der Universität Heidelberg
  • E. Barberio
    • Physics DepartmentSouthern Methodist University
  • D. Dubbers
    • Physikalisches Institut der Universität Heidelberg
  • F. Glück
    • Research Institute for Nuclear and Particle Physics
  • J. C. Hardy
    • Cyclotron InstituteTexas A&M University
  • W. J. Marciano
    • Brookhaven National Laboratory Upton
  • A. Serebrov
    • Petersburg Nuclear Physics Institute
  • N. Severijns
    • Instituut voor Kern- en StralingsfysicaKatholieke Universiteit Leuven
experimental physics

DOI: 10.1140/epjc/s2003-01574-8

Cite this article as:
Abele, H., Barberio, E., Dubbers, D. et al. Eur. Phys. J. C (2004) 33: 1. doi:10.1140/epjc/s2003-01574-8


In the Standard Model of elementary particles, quark-mixing is expressed in terms of a 3 x 3 unitary matrix V, the so called Cabibbo-Kobayashi-Maskawa (CKM) matrix. Significant unitarity checks are so far possible for the first row of this matrix. This article reviews the experimental and theoretical information on these matrix elements. On the experimental side, we find a 2.2 \(\sigma\) to 2.7 \(\sigma\) deviation from unitarity, which conflicts with the Standard Model.

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© Springer-Verlag Berlin/Heidelberg 2004