CP -odd window into long distance dynamics in rare semileptonic B decays

Abstract

We consider the combined measurements of CP-averaged decay rates and direct CP asymmetries of B±→K±ℓ+ℓ− and B±→π±ℓ+ℓ− to probe (nonlocal) four-quark operator matrix element contributions to rare semileptonic B meson decays. We also explore how their effects could be in principle disentangled from possible local new physics effects using U-spin relations. To this end, we construct a ratio of CP-odd decay rate differences which are exactly predicted within the standard model in the U-spin limit, while the leading U-spin breaking effects can also be systematically calculated. Our results motivate binned measurements of the direct CP asymmetry in B±→π±ℓ+ℓ− as well as dedicated theoretical estimates of U-spin breaking both in local form factors as well as in four-quark matrix elements. Published by the American Physical Society 2024