Subproject C1: Strong interaction effects in B meson decays

Project Leaders:
Dr. Rainer Sommer, DESY Zeuthen

B physics experiments of the past decade have confirmed the Kobayashi-Maskawa mechanism of CP violation in its essence, but leave open the possibility of small deviations, or deviations in specific flavour-changing transitions. B decays with hadrons in the final state are numerous and well suited to investigate this question. However, the presence of hadrons implies that strong interaction effects must be addressed together with the CP-violating and flavour-changing phenomena of interest.

This project is devoted to a quantitative understanding of the strong interaction in B decays with perturbative (QCD factorization) and non-perturbative (Heavy Quark Effective Theory on the lattice) methods. The focus is on exclusive decays: leptonic, semi-leptonic as well as non-leptonic two-body.

Heavy Quark Effective Theory

The non-perturbative renormalization of the theory has been tested and applied in the quenched approximation. Remaining work concerns components of the weak flavour currents other than the time-component of the axial current used for fB. The emphasis is on the application with dynamical fermions in collaboration with project B2. For controlling the chiral extrapolation, the leading low energy constant in the heavy meson chiral Lagrangian is computed and then applied in fits describing the light-quark mass dependence of observables. Decay constants of B and Bs, the b-quark mass and form factors of semileptonic decays (close to q2max) are being computed. All numerical computations are carried out at a series of lattice spacings to be able to reach continuum results by a controlled extrapolation.

Exclusive B-Meson Decays

We concentrate on the following areas:

  1. Radiative corrections:
    calculation of the non-leptonic decay tree and penguin amplitudes in QCD factorization at next-to-next-to-leading order both for the vertex term and for spectator-scattering .
  2. B decay phenomenology:
    Re-analysis of decays to two pseudoscalar and one pseudoscalar and one vector meson given the new input from item a; determination of the CKM angle γ. Combination of the QCD factorization approach with SU(3) symmetry for non-leptonic and electroweak penguin decays.
  3. Conceptual studies:
    investigation of the factorization properties of 1/mb suppressed penguin amplitudes, and the calculation of one-loop corrections to them; investigation of ``endpoint divergences'' that prevent the straight-forward application of soft-collinear effective theory to power-suppressed effects.

Last Change: 12th April 2012