Work

Probing unknown nonperturbative effects in b → s ℓ ℓ with inclusive and exclusive observables

Year: 2026

Type: article

Abstract: In this paper we revisit, from a different perspective, a long-standing question: “Is the systematic deficit observed in all branching ratios mediated by a b → s μ μ transition due to new physics, or to a hypothetical constant unknown universal hadronic contribution that mimics new physics?” The key observation that allows us to distinguish between these two possibilities is that nonperturbative contributions associated with c c ¯ loops affect inclusive B → X s ℓ ℓ and exclusive B → K ( * ) ℓ ℓ modes differently. In inclusive decays, factorizable contributions are exactly determined from data on e + e − → hadrons , while nonfactorizable corrections are described by resolved-photon contributions at low q 2 and by local power corrections at high q 2 . In exclusive decays, by contrast, hypothetical charming-penguin effects, beyond those already included in current uncertainty estimates, could appear, in a worst-case scenario, as a constant, universal contribution that it seems, in principle, indistinguishable from genuine new physics. We identify two observables, constructed from ratios of exclusive to inclusive modes, that can discriminate between a new physics contribution and a constant hadronic contribution. Moreover, these ratios can be measured directly by LHCb, as they do not require any normalization to J / ψ K ( * ) branching fractions from B factories. A preliminary evaluation of these observables with present data shows some preference for the new physics interpretation. In a complementary test, a comparison between inclusive measurements and the corresponding sum of exclusive modes at high q 2 similarly disfavors an explanation based on a constant hadronic contribution. Finally, we provide projections for the new observables based on expected LHCb and Belle II measurements in the near future.

Source: Physical review. D/Physical review. D.

DOI: 10.1103/zrp8-84fg

Authors: P. Alvarez-Cartelle, B. Capdevila, E. Lunghi, J. Matias