Quark mixing, CKM unitarity - The unitarity problemH. Abele, E. Barberio, D. Dubbers, F. Glück, J. C. Hardy, W. J. Marciano, A. Serebrov and N. SeverijnsEur. Phys. J. C, 33 1 (2004) 1-8DOI: https://doi.org/10.1140/epjc/s2003-01574-8