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How much space is left for a new family of fermions?

Bobrowski, M.; Lenz, A.; Riedl, J.; Rohrwild, J.


M. Bobrowski

A. Lenz

J. Riedl

J. Rohrwild


We perform an exploratory study of the allowed parameter range for the CKM-like mixing of hypothetical quarks of a fourth generation. As experimental constraints we use the tree-level determinations of the 3×3 Cabibbo-Kobayashi-Maskawa (CKM) elements and flavor-changing neutral current (FCNC) processes (K, D, Bd, Bs mixing and the decay b→sγ) under the assumption that the 4×4 CKM matrix is unitary. For the FCNCs we use some simplifying assumptions concerning the QCD corrections. Typically small mixing with the fourth family is favored; contrary to expectation, however, we find that also a quite large mixing with the fourth family is not yet excluded.


Bobrowski, M., Lenz, A., Riedl, J., & Rohrwild, J. (2009). How much space is left for a new family of fermions?. Physical Review D, 79(11), Article 113006.

Journal Article Type Article
Publication Date 2009-06
Deposit Date Nov 19, 2012
Journal Physical Review D
Print ISSN 1550-7998
Electronic ISSN 1550-2368
Publisher American Physical Society
Peer Reviewed Peer Reviewed
Volume 79
Issue 11
Article Number 113006