Endpoint anatomy of the baryon--meson sum rule in b→ sνν̅
Abstract
Baryon-meson sum rules enable cross-checks among exclusive mesonic and baryonic measurements. Unlike their heavy-to-heavy counterparts, analogous heavy-to-light relations lack an explicit heavy-quark-symmetry origin. We investigate their origin in the b→ sνν̅ system by studying the relevant helicity amplitudes at the two kinematic endpoints. Although the sum rule follows algebraically from the simple short-distance structure, its coefficient depends nontrivially on the hadronic dynamics. At maximum recoil, the coefficient for the daughter baryons cal B=Λ,Ξ is consistent with the approximate value 1/2 within current form-factor uncertainties. At zero recoil, by contrast, a kinematic helicity projection enforces its exact vanishing. The fully integrated coefficients are numerically close to 1/4. However, unlike the one-quarter coefficient in the heavy-to-heavy system, they are not local symmetry coefficients but integrated quantities shaped by the behavior between the two endpoints. This understanding may guide the construction of baryon-meson sum rules in more general heavy-to-light decays.
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BibTeX
@misc{iguro2026endpoint,
title = {{Endpoint anatomy of the baryon--meson sum rule in $b\to sν\barν$}},
author = {Syuhei Iguro},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.21253},
eprint = {2609.21253},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.21253},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Endpoint anatomy of the baryon--meson sum rule in b→ sνν̅
AU - Syuhei Iguro
PY - 2026
DA - 2026/09/18
PB - arXiv
DO - 10.48550/arxiv.2609.21253
UR - https://arxiv.org/abs/2609.21253
AB - Baryon-meson sum rules enable cross-checks among exclusive mesonic and baryonic measurements. Unlike their heavy-to-heavy counterparts, analogous heavy-to-light relations lack an explicit heavy-quark-symmetry origin. We investigate their origin in the b→ sνν̅ system by studying the relevant helicity amplitudes at the two kinematic endpoints. Although the sum rule follows algebraically from the simple short-distance structure, its coefficient depends nontrivially on the hadronic dynamics. At maximum recoil, the coefficient for the daughter baryons cal B=Λ,Ξ is consistent with the approximate value 1/2 within current form-factor uncertainties. At zero recoil, by contrast, a kinematic helicity projection enforces its exact vanishing. The fully integrated coefficients are numerically close to 1/4. However, unlike the one-quarter coefficient in the heavy-to-heavy system, they are not local symmetry coefficients but integrated quantities shaped by the behavior between the two endpoints. This understanding may guide the construction of baryon-meson sum rules in more general heavy-to-light decays.
ER -