Disentangling Vud from New Physics in Beta Decays with the FCC-ee
Abstract
Superallowed nuclear β-decays enable the most precise determination of the CKM element Vud, but they are only sensitive to an effective combination of Vud and New Physics contributions to left-handed charged currents, which low-energy data alone cannot disentangle. Here we determine Vud simultaneously with the relevant Wilson coefficients of the Standard Model Effective Field Theory (SMEFT) by combining, within the SMEFiT framework, a dedicated likelihood for superallowed transitions, including radiative and nuclear-structure uncertainties, with LEP and LHC world data and HL-LHC and FCC-ee projections. Current collider data and HL-LHC projections only partially lift the degeneracy between Vud and possible New Physics effects. Instead, the FCC-ee fully decouples Vud from New Physics, recovering SM-level precision while significantly tightening the constraints on the SMEFT Wilson coefficients. This conclusion is robust against variations in flavour assumptions and theory uncertainties. Our results highlight the complementarity between future colliders and low-energy experiments, and pave the way towards a SMEFT-consistent interpretation of first-row CKM unitarity tests and the Cabibbo angle anomaly.
Related
- Neutrinoless Double-Beta Decays from Operator Mixing
- A comprehensive theory framework for perturbative calculations of δC in superallowed beta decays
- Higher-order corrections to beta decays and nuclear structure
- Influence of configuration-interaction on isospin impurities and isospin symmetry breaking corrections to superallowed 0+→ 0+ beta decays
- Disentangling Measurement Protocol from Material Physics in Isotypic and Anisotypic SiC/Si Heterojunctions: A Metrology-Driven Study for Betavoltaic Energy Conversion
BibTeX
@misc{gialidi2026disentangling,
title = {{Disentangling $V_ud$ from New Physics in Beta Decays with the FCC-ee}},
author = {Lemonia Gialidi and Elie Hammou and Kamil Laurent and Vaisakh Plakkot and Juan Rojo and Jordy de Vries},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.31834},
eprint = {2609.31834},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.31834},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Disentangling V_ud from New Physics in Beta Decays with the FCC-ee
AU - Lemonia Gialidi
AU - Elie Hammou
AU - Kamil Laurent
AU - Vaisakh Plakkot
AU - Juan Rojo
AU - Jordy de Vries
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2609.31834
UR - https://arxiv.org/abs/2609.31834
AB - Superallowed nuclear β-decays enable the most precise determination of the CKM element V_ud, but they are only sensitive to an effective combination of V_ud and New Physics contributions to left-handed charged currents, which low-energy data alone cannot disentangle. Here we determine V_ud simultaneously with the relevant Wilson coefficients of the Standard Model Effective Field Theory (SMEFT) by combining, within the SMEFiT framework, a dedicated likelihood for superallowed transitions, including radiative and nuclear-structure uncertainties, with LEP and LHC world data and HL-LHC and FCC-ee projections. Current collider data and HL-LHC projections only partially lift the degeneracy between V_ud and possible New Physics effects. Instead, the FCC-ee fully decouples V_ud from New Physics, recovering SM-level precision while significantly tightening the constraints on the SMEFT Wilson coefficients. This conclusion is robust against variations in flavour assumptions and theory uncertainties. Our results highlight the complementarity between future colliders and low-energy experiments, and pave the way towards a SMEFT-consistent interpretation of first-row CKM unitarity tests and the Cabibbo angle anomaly.
ER -