2025/02/28 by Herren, Florian, Kubis, Bastian, van Tonder, Raynette · 2 citations
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2502.20960
We introduce a novel parameterization of B→ππℓν 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 B→ππℓν decays through fits to differential spectra of B+ → π+π- ℓ+ ν 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: B(B+→ (π+ π-)S ℓ+ ν) amp;= 2.2+1.4-1.0× 10-5 ,
B(B+→ (π+ π-)P ℓ+ν) amp;= 19.6+2.8-2.7× 10-5 ,
B(B+→ (π+ π-)D ℓ+ ν) amp;= 3.5+1.3-1.1× 10-5 .
In addition, we derive predictions for the thus far unobserved B+→ π0π0ℓ+ν decay and obtain a sizeable branching fraction of B(B+→ π0π0ℓ+ν) = 2.9+0.9-0.7× 10-5.