Smallness of charm-loop effects in B→K(*)ℓℓ at low q2 : Light-meson distribution-amplitude analysis

Abstract

The nonlocal effects originating from the charm quark loops at dilepton invariant masses smaller than the charmonium threshold in B→Kℓℓ are evaluated with light-meson distribution amplitudes. The revised estimates with B-meson distribution amplitude within a light cone sum rule approach yielded results about three orders smaller than the original computation. In view of the importance of these nonfactorizable soft gluon effects, both conceptually and phenomenologically, an independent evaluation is necessary. It is found that to twist-4 accuracy, these soft gluon effects vanish when evaluated employing the kaon distribution amplitude. Similar results hold for B→K*ℓℓ to the leading twist. This eliminates one of the major sources of potential uncertainty which usually makes it difficult for a clear case of new physics, should the data show deviations from the standard model. Published by the American Physical Society 2025