Gubernari, Nico
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Publication Access status: Metadata only , Dispersive analysis of B → K(*) and Bs → ϕ form factors(2023); ; ; We propose a stronger formulation of the dispersive (or unitarity) bounds à la Boyd-Grinstein-Lebed (BGL), which are commonly applied in analyses of the hadronic form factors for B decays. In our approach, the existing bounds are split into several new bounds, thereby disentangling form factors that are jointly bounded in the common approach. This leads to stronger constraints for these objects, to a significant simplification of our numerical analysis, and to the removal of spurious correlations among the form factors. We apply these novel bounds to $$ \overline{B}\to {\overline{K}}^{\left(\ast \right)} $$ and $$ {\overline{B}}_s\to \phi $$ form factors by fitting them to purely theoretical constraints. Using a suitable parametrization, we take into account the form factors’ below-threshold branch cuts arising from on-shell $$ {\overline{B}}_s{\pi}^0 $$ and $$ {\overline{B}}_s{\pi}^0{\pi}^0 $$ states, which so-far have been ignored in the literature. In this way, we eliminate a source of hard-to-quantify systematic uncertainties. We provide machine readable files to obtain the full set of the $$ \overline{B}\to {\overline{K}}^{\left(\ast \right)} $$ and $$ {\overline{B}}_s\to \phi $$ form factors in and beyond the entire semileptonic phase space.Source Type:Article2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Non-factorisable contributions of strong-penguin operators in Λb → Λℓ+ℓ− decays(2024); We investigate for the first time a certain class of non-factorisable contributions of the four-quark operators $$ \mathcal{O} $$ 3 − 6 in the weak effective Hamiltonian to the Λ b → Λ ℓ + ℓ − decay amplitude. We focus on the case where a virtual photon is radiated from one of the light constituents of the Λ b baryon, in the kinematic situation of large hadronic recoil with an energetic Λ baryon in the final state. The effect on the suitably defined “non-local form factors” is calculated using the light-cone sum rule approach for a correlator with an interpolating current for the light Λ baryon. We find that this approach requires the introduction of new soft functions that generalise the standard light-cone distribution amplitudes (LCDAs) for the heavy Λ b baryon. We give a heuristic discussion of their properties and a model that relates them to the standard LCDAs. Within this framework, we provide numerical results for the size of the non-local form factors considered.Source Type:Article12
