arXiv subjects

Frederic Noël

Publications and source records attributed to Frederic Noël.

6 recordsLinked to original sources

arXiv2026

Ab initio calculations of parity-violating electron scattering off $^{48}$Ca and $^{208}$Pb

Parity-violating electron scattering off nuclei both serves as a low-energy precision probe to test electroweak interactions and allows one to access neutron distributions inside nuclei. It has implications for strong interactions in dense neutron-rich environments, also providing constraints for the properties of matter in neutron stars. Precision measurements are available for $^{48}$Ca and $^{208}$Pb by the CREX and PREX collaborations, respectively, and their interpretation requires advanced nuclear-structure calculations to draw firm conclusions. We perform the first ab initio calculations of the parity-violating asymmetry $A_\text{PV}$ based on nuclear forces from chiral effective field theory, fully including corrections due to Coulomb distortion effects. Based on these results, we critically reexamine correlation analyses employed to infer weak radii and quantify the resulting tensions between ab initio and experimental results. We find that ab initio calculations prefer values of $A_\text{PV}$ slightly smaller and larger than observed for $^{48}$Ca and $^{208}$Pb, respectively, with a global significance of $1.9σ$. Using theoretically consistent inputs for charge and weak densities, we infer from the experimental $A_\text{PV}$ a neutron skin of $^{208}$Pb of $R_n-R_p = 0.187(25)(18)$ fm, substantially smaller than that reported by PREX II.

nucl-th↗

arXiv2025

Ab initio calculations of overlap integrals for $μ\to e$ conversion in nuclei

The rate for $μ\to e$ conversion in nuclei is set to provide the most stringent test of lepton-flavor symmetry and a window into physics beyond the Standard Model. However, to disentangle new lepton-flavor-violating interactions, in combination with information from $μ\to eγ$ and $μ\to 3e$, it is critical that uncertainties at each step of the analysis be controlled and fully quantified. In this regard, nuclear response functions related to the coupling to neutrons are notoriously problematic, since they are not directly constrained by experiment. We address these shortcomings by combining ab initio calculations with a recently improved determination of charge distributions from electron scattering by exploiting strong correlations among charge, point-proton, and point-neutron radii and densities. We present overlap integrals for $^{27}$Al, $^{48}$Ca, and $^{48}$Ti including full covariance matrices, allowing, for the first time, for a comprehensive consideration of nuclear structure uncertainties in the interpretation of $μ\to e$ experiments.

nucl-th↗

arXiv2024

On the scalar $πK$ form factor beyond the elastic region

Pion-kaon ($πK$) final states, often appearing in heavy-particle decays at the precision frontier, are important for Standard-Model tests, to describe crossed channels with exotic states, and for spectroscopy of excited kaon resonances. We construct a representation of the $πK$ $S$-wave form factor using the elastic $πK$ scattering phase shift via dispersion relations in the elastic region and extend this model into the inelastic region using resonance exchange, while maintaining unitarity and the correct analytic structure. As a first application, we successfully described the $τ\to K_S πν_τ$ spectrum to not only achieve a better distinction between $S$- and $P$-wave contributions, but also to provide an improved estimate of the $CP$ asymmetry produced by a tensor operator as well as the forward-backward asymmetry, both of which can be confronted with future data at Belle II.

hep-ph↗

arXiv2024

Uncertainty quantification for $μ\to e$ conversion in nuclei: charge distributions

Predicting the rate for $μ\to e$ conversion in nuclei for a given set of effective operators mediating the violation of lepton flavor symmetry crucially depends on hadronic and nuclear matrix elements. In particular, the uncertainties inherent in this non-perturbative input limit the discriminating power that can be achieved among operators by studying different target isotopes. In order to quantify the associated uncertainties, as a first step, we go back to nuclear charge densities and propagate the uncertainties from electron scattering data for a range of isotopes relevant for $μ\to e$ conversion in nuclei, including $^{40,48}$Ca, $^{48,50}$Ti, and $^{27}$Al. We provide as central results Fourier-Bessel expansions of the corresponding charge distributions with complete covariance matrices, accounting for Coulomb-distortion effects in a self-consistent manner throughout the calculation. As an application, we evaluate the overlap integrals for $μ\to e$ conversion mediated by dipole operators. In combination with modern ab-initio methods, our results will allow for the evaluation of general $μ\to e$ conversion rates with quantified uncertainties.

nucl-th↗

arXiv2023

Improved limits on lepton-flavor-violating decays of light pseudoscalars via spin-dependent $μ\to e$ conversion in nuclei

Lepton-flavor-violating decays of light pseudoscalars, $P=π^0,η,η'\toμe$, are stringently suppressed in the Standard Model up to tiny contributions from neutrino oscillations, so that their observation would be a clear indication for physics beyond the Standard Model. However, in effective field theory such decays proceed via axial-vector, pseudoscalar, or gluonic operators, which are, at the same time, probed in spin-dependent $μ\to e$ conversion in nuclei. We derive master formulae that connect both processes in a model-independent way in terms of Wilson coefficients, and study the implications of current $μ\to e$ limits in titanium for the $P\toμe$ decays. We find that these indirect limits surpass direct ones by many orders of magnitude.

hep-ph↗

arXiv2021

On the scalar $πK$ form factor beyond the elastic region

Pion-kaon ($πK$) pairs occur frequently as final states in heavy-particle decays. A consistent treatment of $πK$ scattering and production amplitudes over a wide energy range is therefore mandatory for multiple applications: in Standard Model tests; to describe crossed channels in the quest for exotic hadronic states; and for an improved spectroscopy of excited kaon resonances. In the elastic region, the phase shifts of $πK$ scattering in a given partial wave are related to the phases of the respective $πK$ form factors by Watson's theorem. Going beyond that, we here construct a representation of the scalar $πK$ form factor that includes inelastic effects via resonance exchange, while fulfilling all constraints from $πK$ scattering and maintaining the correct analytic structure. As a first application, we consider the decay ${τ\to K_Sπν_τ}$, in particular, we study to which extent the $S$-wave $K_0^*(1430)$ and the $P$-wave $K^*(1410)$ resonances can be differentiated and provide an improved estimate of the $CP$ asymmetry produced by a tensor operator. Finally, we extract the pole parameters of the $K_0^*(1430)$ and $K_0^*(1950)$ resonances via Padé approximants, $\sqrt{s_{K_0^*(1430)}}=[1408(48)-i\, 180(48)]$ MeV and $\sqrt{s_{K_0^*(1950)}}=[1863(12)-i\,136(20)]$ MeV, as well as the pole residues. A generalization of the method also allows us to formally define a branching fraction for ${τ\to K_0^*(1430) ν_τ}$ in terms of the corresponding residue, leading to the upper limit ${\text{BR}(τ\to K_0^*(1430) ν_τ)<1.6 \times 10^{-4}}$.

hep-ph↗