We calculate the hard-scattering kernels relevant to the negative-helicity decay amplitude in B decays to two vector mesons in the framework of QCD factorisation. We then perform a comprehensive analysis of the 34 B → V V decays, including B s decays and the complete set of polarisation observables. We find considerable uncertainties from weak annihilation and the non-factorisation of spectatorscattering. Large longitudinal polarisation is expected with certainty only for a few tree-dominated colour-allowed modes, which receive small penguin and spectatorscattering contributions. This allows for an accurate determination of the CKM angle α (or γ) from S ρρ L resulting in α = (85.6 +7.4 −7.3 ) • We also emphasize that the ρK * system is ideal for an investigation of electroweak penguin effects.

We complete the investigation of loop corrections to hard spectator-scattering in exclusive B meson to light meson transitions by computing the short-distance coefficient (jet-function) from the hard-collinear scale. Adding together the two coefficients from matching QCD → SCET I → SCET II , we investigate the size of loop effects on the ratios of heavy-to-light meson form factors at large recoil. We find the corrections from the hard and hard-collinear scales to be of approximately the same size, and significant, but the perturbative expansions appear to be wellbehaved. Our calculation provides a non-trivial verification of the factorization arguments. We observe considerable differences between the predictions based on factorization in the heavy-quark limit and current QCD sum rule calculations of the form factors. We also include the hard-collinear correction in the B → ππ tree amplitudes, and find an enhancement of the colour-suppressed amplitude relative to the colour-allowed amplitude. separated in SCET, the short-distance coefficients T i pertaining to spectator-scattering are represented as convolutions C (B1) i ⋆ J with the two factors associated with the two different scales.In the limit that not only power corrections in Λ/m b but also radiative corrections in the strong coupling α s are neglected, the second term on the right hand side of (1) is absent, and parameter-free relations between ratios of form factors follow [7]. The α s contributions to (1) have been computed in [8], and the spectator-scattering term T i has been found to dominate the correction. This motivates an investigation of the subsequent term in the perturbative expansion of T i . Since the leading α s term is due to a tree diagram with gluon exchange between the current quarks and the spectator anti-quark, this amounts to the computation of the 1-loop correction to spectator-scattering. Since

We compute the one-loop (hard) matching correction to heavy-to-light transition currents in soft-collinear effective theory (SCET) to sub-leading power in the SCET expansion parameter for an arbitrary Dirac structure of the QCD weak current.

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We discuss a novel electromagnetic penguin contribution to the transverse helicity amplitudes in B decays to two vector mesons, which is enhanced by two powers of mB/Lambda relative to the standard penguin amplitudes. This leads to unique polarization signatures in penguin-dominated decay modes such as B-->rhoK* similar to polarization effects in the radiative decay B-->K*gamma and offers new opportunities to probe the magnitude and chirality of flavor-changing neutral current couplings to photons.