arXiv subjects

Joanna E. Sobczyk

Publications and source records attributed to Joanna E. Sobczyk.

9 recordsLinked to original sources

arXiv2026

Impact of ab initio E1 strength on neutron capture rates along the nickel isotopic chain

Nucleosynthesis simulations of the r-process require neutron capture rates for neutron-rich nuclei, many of which lie beyond experimental reach. Predicting these rates relies on theoretical calculations of the low-energy electric dipole (E1) strength near the neutron threshold. We present the first ab initio computation of the E1 strength along the nickel isotopic chain, for $^{58}$Ni and the even-even isotopes $^{68-80}$Ni. The E1 strength is obtained with the Lorentz integral transform coupled-cluster (LIT-CC) method, extended to axially symmetric reference states to reach open-shell nuclei, using two- and three-nucleon interactions from chiral effective field theory. The approach is benchmarked against the measured photoabsorption cross section of $^{58}$Ni and the E1 strength of $^{68}$Ni. Along the chain we find low-lying E1 strength above the neutron threshold that grows with neutron number. Including it in the reaction code TALYS enhances the neutron capture rates forming $^{68-78}$Ni between 3 and 10 GK, with an effect that increases with temperature and neutron number and an uncertainty dominated by the inversion of the integral transform. For $^{80}$Ni, where strong pygmy dipole strength lies just above threshold, the enhancement sets in already around 0.5 GK. Together, these results open the way to ab initio input for neutron capture rates along isotopic chains far from stability.

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arXiv2026

Modeling quasielastic lepton-nucleus interactions with ab initio spectral functions from infinite nuclear matter

We present a study of quasielastic lepton-nucleus scattering within the local density approximation, using ab initio spectral functions from infinite nuclear matter derived with self-consistent Green's functions theory and interpolated by neural networks. We include final-state interactions in terms of the particle spectral function and investigate the importance and range of validity of this treatment for varying momentum transfer. The performance of the model is tested for inclusive electron scattering on different isospin-symmetric target nuclei, and we present results for $^{12}$C, $^{16}$O, and $^{40}$Ca. Theoretical uncertainties originating from the neural network interpolation and the Hamiltonian dependence are assessed. We also present a calculation of charged-current responses of $^{16}$O and the flux-averaged total $ν_μ-^{12}$C cross section. Our model shows good agreement with experimental data within the range of validity of our approximations. The framework can be readily extended to include additional dynamical mechanisms, such as pion production, as well as other nuclear Hamiltonians.

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arXiv2025

Optimized binning for response function reconstruction via Chebyshev expansions

We propose an optimized histogram binning strategy to reconstruct nuclear response functions via the Chebyshev expansion bound-state method. Our approach employs a stochastic regularization of the density of states to define adaptive, equal-area bins. Using the deuteron solved in a harmonic-oscillator basis with a chiral interaction, we benchmark on dipole and longitudinal responses, obtaining excellent agreement with exact theory and experiment. This general framework readily extends to other many-body systems and opens the door to new ab initio calculations of lepton-nucleus cross sections in medium-mass nuclei.

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arXiv2024

16O electroweak response functions from first principles

We present calculations of various electroweak response functions for the 16O nucleus obtained using coupled-cluster theory in conjunction with the Lorentz integral transform method. We employ nuclear forces derived at next-to-leading order and next-to-next-to-leading order in chiral effective field theory and perform a Bayesian analysis to assess uncertainties. Our results are in good agreement with available electron-scattering data at q~ 326 MeV/c. Additionally, we provide several predictions for the weak response functions in the quasi-elastic peak region at q= 300 and 400 MeV/c, which are critical for long-baseline neutrino experiments.

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arXiv2024

Modeling inclusive electron-nucleus scattering with Bayesian artificial neural networks

We introduce a Bayesian protocol based on artificial neural networks that is suitable for modeling inclusive electron-nucleus scattering on a variety of nuclear targets with quantified uncertainties. Unlike previous applications in the field, which directly parameterize the cross sections, our approach employs artificial neural networks to represent the longitudinal and transverse response functions. In contrast to cross sections, which depend on the incoming energy, scattering angle, and energy transfer, the response functions are determined solely by the energy and momentum transfer to the system, allowing the angular component to be treated analytically. We assess the accuracy and predictive power of our framework against the extensive data in the quasielastic inclusive electron-scattering database. Additionally, we present novel extractions of the longitudinal and transverse response functions and compare them with previous experimental analysis and nuclear ab-initio calculations.

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arXiv2024

Electron scattering on $^4$He from coupled-cluster theory

We present a coupled-cluster calculation for the electron-$^4$He scattering in the region of the quasi-elastic peak. We show the longitudinal and transverse responses separately, and discuss results within two distinct theoretical methods: the Lorentz integral transform and spectral functions. The comparison between them allows to investigate the role of final state interactions, two-body currents and relativistic effects.

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arXiv2023

$^{16}$O spectral function from coupled-cluster theory: applications to lepton-nucleus scattering

We calculate the $^{16}$O spectral function by combining coupled-cluster theory with a Gaussian integral transform and by expanding the integral kernel in terms of Chebyshev polynomials to allow for a quantification of the theoretical uncertainties. We perform an analysis of the spectral function and employ it to predict lepton-nucleus scattering. Our results well describe the $^{16}$O electron scattering data in the quasi-elastic peak for momentum transfers $|\mathbf{q}|\gtrapprox500$ MeV and electron energies up to 1.2 GeV, extending therefore the so-called first principles approach to lepton-nucleus cross sections well into the relativistic regime. To prove the applicability of this method to neutrino-nucleus cross sections, we implement our $^{16}$O spectral functions in the NuWro Monte Carlo event generator and provide a comparison with recently published T2K neutrino data.

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arXiv2022

Uncertainty quantification in electromagnetic observables of nuclei

We present strategies to quantify theoretical uncertainties in modern ab-initio calculations of electromagnetic observables in light and medium-mass nuclei. We discuss how uncertainties build up from various sources, such as the approximations introduced by the few- or many-body solver and the truncation of the chiral effective field theory expansion. We review the recent progress encompassing a broad range of electromagnetic observables in stable and unstable nuclei.

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arXiv2021

Spectral density reconstruction with Chebyshev polynomials

Accurate calculations of the spectral density in a strongly correlated quantum many-body system are of fundamental importance to study its dynamics in the linear response regime. Typical examples are the calculation of inclusive and semi-exclusive scattering cross sections in atomic nuclei and transport properties of nuclear and neutron star matter. Integral transform techniques play an important role in accessing the spectral density in a variety of nuclear systems. However, their accuracy is in practice limited by the need to perform a numerical inversion which is often ill-conditioned. In the present work we extend a recently proposed quantum algorithm which circumvents this problem. We show how to perform controllable reconstructions of the spectral density over a finite energy resolution with rigorous error estimates. An appropriate expansion in Chebyshev polynomials allows for efficient simulations also on classical computers. We apply our idea to reconstruct a simple model -- response function as a proof of principle. This paves the way for future applications in nuclear and condensed matter physics.

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