experimental physics

The European Physical Journal C - Particles and Fields

, Volume 33, Issue 1, pp 1-8

First online:

Quark mixing, CKM unitarity

The unitarity problem
  • H. AbeleAffiliated withPhysikalisches Institut der Universität Heidelberg
  • , E. BarberioAffiliated withPhysics Department, Southern Methodist University
  • , D. DubbersAffiliated withPhysikalisches Institut der Universität Heidelberg
  • , F. GlückAffiliated withResearch Institute for Nuclear and Particle Physics
  • , J. C. HardyAffiliated withCyclotron Institute, Texas A&M University
  • , W. J. MarcianoAffiliated withBrookhaven National Laboratory Upton
  • , A. SerebrovAffiliated withPetersburg Nuclear Physics Institute
  • , N. SeverijnsAffiliated withInstituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access


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.