Constraints on the CKM angle \(\gamma\) and strong phases from \(B\to\pi K\) decays

  • A.J. Buras
  • R. Fleischer
Theoretical physics


As we pointed out recently, the neutral decays \(B_d\to\pi^\mp K^\pm\) and \(B_d\to\pi^0K\) may provide non-trivial bounds on the CKM angle \(\gamma\). In this paper, we reconsider this approach in the light of recent CLEO data, which look very interesting. In particular, the results for the corresponding CP-averaged branching ratios are in favour of strong constraints on \(\gamma\), where the second quadrant is preferred. Such a situation would be in conflict with the standard analysis of the unitarity triangle. Moreover, constraints on a CP-conserving strong phase \(\delta_{\rm n}\) are in favour of a negative value of \(\cos\delta_{\rm n}\), which would be in conflict with the factorization expectation. In addition, there seems to be an interesting discrepancy with the bounds that are implied by the charged \(B\to\pi K\) system: whereas these decays favour a range for \(\gamma\) that is similar to that of the neutral modes, they point towards a positive value of \(\cos\delta_{\rm c}\), which would be in conflict with the expectation of equal signs for \(\cos\delta_{\rm n}\) and \(\cos\delta_{\rm c}\). If future data should confirm this “puzzle”, it may be an indication for new-physics contributions to the electroweak penguin sector, or a manifestation of large non-factorizable SU(3)-breaking effects.


Standard Analysis Strong Constraint Future Data Interesting Discrepancy Equal Sign 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • A.J. Buras
    • 1
  • R. Fleischer
    • 2
  1. 1.Technische Universität München, Physik Department, 85748 Garching, Germany DE
  2. 2.Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany DE

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