paper

A model-independent parameterization of decays

arXiv:2502.20960 · doi:10.1103/8pm6-9xzq

Abstract

We introduce a novel parameterization of form factors relying on partial-wave decompositions and series expansions in suitable variables. We bound the expansion coefficients through unitarity and include left-hand cut contributions using established dispersive methods. The two-hadron lineshapes are treated in a model-independent manner using Omnès functions, thus allowing for a data-driven determination of the expansion parameters. We study the underlying composition of the di-pion system in decays through fits to differential spectra of measured by the Belle experiment. In contrast to previous works, we are able to study the full phase-space and are not limited to certain kinematic regions. As a consequence, we extract branching fractions for the different partial waves of the di-pion system. We find: \begin{align*} \mathcal{B}(B^+\rightarrow (π^+ π^-)_S \ell^+ ν) &= 2.2^{+1.4}_{-1.0}\times 10^{-5}\,,\\ \mathcal{B}(B^+\rightarrow (π^+ π^-)_P \ell^+ν) &= 19.6^{+2.8}_{-2.7}\times 10^{-5}\,,\\ \mathcal{B}(B^+\rightarrow (π^+ π^-)_D \ell^+ ν) &= 3.5^{+1.3}_{-1.1}\times 10^{-5}\,.\\ \end{align*} In addition, we derive predictions for the thus far unobserved decay and obtain a sizeable branching fraction of .

arXiv comment22 pages, 11 amazing figures; v2: typos corrected, version as published in PRD

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