Impact of Hadronic Resonances on B→ K(*)τ+τ- Decays
Abstract
Neutral-current semileptonic B decays are plagued by hadronic resonances across the dilepton invariant-mass squared spectrum, q2. For light leptons, ℓ=e,μ, these resonances can be avoided with suitable q2 cuts. This strategy is less straightforward for τ modes, where missing energy from the τ decay makes q2 difficult to reconstruct. In fact, while Belle II is able to discriminate between different regions in q2 due to its clean environment, this is not directly possible in a hadronic one. Therefore, the interpretation of b→ sτ+τ- measurements from e.g. LHCb, CMS requires the description of these resonant effects. In this article, we adopt a different strategy by including the resonant contributions (in particular from ψ(2S)) into our predictions for B→ K(*)τ+τ- decays, instead of avoiding them. We provide predictions for different initial kinematic points (4mτ2, 14.18GeV2 and 15GeV2) that can be convenient for LHCb, CMS and Belle II. For this, we use a data-driven approach based on the LHCb measurements of B→ K(*)μ+μ- decays. Including the resonances and integrating over the full q2 range substantially enhances the Standard Model predictions. However, for sufficiently large New Physics, motivated by the current tensions in R(D(*)) and B→ K(*)νν decays, the short-distance contribution becomes comparable to or even exceeds the resonant one. This highlights two advantages of this strategy: it exploits the additional phase space associated with the resonant regions to probe large New Physics contributions, and it enables the use of hadron-collider data, where the resonances cannot be resolved. We further quantify how including or neglecting the resonances affects the total branching ratio as a function of New Physics contributions and, equivalently, of the experimental precision.
Related
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BibTeX
@misc{balta2026impact,
title = {{Impact of Hadronic Resonances on $B\to K^(*)τ^+τ^-$ Decays}},
author = {Guillermo Baltà and Andreas Crivellin and Rafel Escribano and Joaquim Matias and Martín Novoa-Brunet},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2605.21291},
eprint = {2605.21291},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.21291},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Impact of Hadronic Resonances on B→ K^(*)τ^+τ^- Decays
AU - Guillermo Baltà
AU - Andreas Crivellin
AU - Rafel Escribano
AU - Joaquim Matias
AU - Martín Novoa-Brunet
PY - 2026
DA - 2026/10/06
PB - arXiv
DO - 10.48550/arxiv.2605.21291
UR - https://arxiv.org/abs/2605.21291
AB - Neutral-current semileptonic B decays are plagued by hadronic resonances across the dilepton invariant-mass squared spectrum, q^2. For light leptons, ℓ=e,μ, these resonances can be avoided with suitable q^2 cuts. This strategy is less straightforward for τ modes, where missing energy from the τ decay makes q^2 difficult to reconstruct. In fact, while Belle II is able to discriminate between different regions in q^2 due to its clean environment, this is not directly possible in a hadronic one. Therefore, the interpretation of b→ sτ^+τ^- measurements from e.g. LHCb, CMS requires the description of these resonant effects. In this article, we adopt a different strategy by including the resonant contributions (in particular from ψ(2S)) into our predictions for B→ K^(*)τ^+τ^- decays, instead of avoiding them. We provide predictions for different initial kinematic points (4m_τ^2, 14.18GeV^2 and 15GeV^2) that can be convenient for LHCb, CMS and Belle II. For this, we use a data-driven approach based on the LHCb measurements of B→ K^(*)μ^+μ^- decays. Including the resonances and integrating over the full q^2 range substantially enhances the Standard Model predictions. However, for sufficiently large New Physics, motivated by the current tensions in R(D^(*)) and B→ K^(*)νν decays, the short-distance contribution becomes comparable to or even exceeds the resonant one. This highlights two advantages of this strategy: it exploits the additional phase space associated with the resonant regions to probe large New Physics contributions, and it enables the use of hadron-collider data, where the resonances cannot be resolved. We further quantify how including or neglecting the resonances affects the total branching ratio as a function of New Physics contributions and, equivalently, of the experimental precision.
ER -