Exclusive Chromomagnetism in heavy-to-light FCNCs

Preprint number: CP3-Origins-2012-29 and DIAS-2012-30
Authors: Maria Dimou (Southampton University), James Lyon (Edinburgh University), and Roman Zwicky (Edinburgh University & CP3-Origins & DIAS)
External link: arXiv.org

We compute matrix elements of the chromomagnetic operator, often denoted by O8, between B/D-states and light mesons plus an off-shell photon by employing the method of light-cone sum rules (LCSR) at leading twist-2. These matrix elements are relevant for processes such as B → K* l+l and they can be seen as the analogues of the well-known penguin form factors T1,2,3 and fT. We find a large CP-even phase for which we give a long-distance (LD) interpretation. We compare our results to QCD factorisation for which the spectator photon emission is end-point divergent. The analytic structure of the correlation function used in our method admits a complex anomalous threshold on the physical sheet. The meaning and handling within the sum rule approach of the anomalous threshold is discussed.