arXiv subjects

Carlotta Giusti

Publications and source records attributed to Carlotta Giusti.

At least 19 recordsLinked to original sources

arXiv2026

A Phenomenological Extension for Microscopic Optical Potentials

Microscopic optical potentials constructed from realistic nucleon-nucleon interactions via multiple-scattering theory provide a first-principles description of nucleon-nucleus scattering. Nevertheless, such approaches often neglect medium corrections beyond Pauli blocking and fail to fully capture higher-order scattering contributions, leading to systematic under-prediction of absorption and deficiencies in angular distributions at low and intermediate energies. In this work we introduce a phenomenological correction scheme with an energy-dependent term designed to mimic correlation effects, dispersive contributions, and multi-step scattering processes. The correction is implemented in a minimal form to preserve the predictive character of the underlying microscopic model, while enabling improved flexibility in describing experimental observables. Applications to proton and neutron elastic scattering on light-mass nuclei demonstrate that the modified potentials yield enhanced agreement with measured differential cross sections, without sacrificing the microscopic foundation. This approach provides a practical pathway for incorporating missing medium and higher-order effects into optical model analyses relevant for nuclear structure and reaction studies.

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arXiv2026

Inelastic nucleon-nucleus scattering from a microscopic point of view

We apply to the nucleon-nucleus inelastic process a fully coherent microscopic multiple scattering approach. Our study addresses the complexities inherent in characterizing inelastic scattering events, offering a comprehensive theoretical model grounded in the reaction theory. The approach is based on the distorted-wave approximation and requires the knowledge of three potentials, which give the initial and final distorted wave functions and the transition potential. All of them are derived just like the microscopic optical potential for elastic nucleon-nucleus scattering we derived in previous papers of ours within the framework of the Watson multiple scattering theory and adopting the impulse approximation. The potentials are obtained by folding nonlocal ab initio nuclear densities from the No-Core Shell Model (NCSM) with a nucleon-nucleon $t$ matrix computed with a chiral interaction consistent with the one used in the calculation of the density. The only difference in the formal expressions of the three potentials resides in the nuclear density, where we use the ground and excited state densities of the target and the transition density. By extending methods traditionally applied to elastic scattering, we incorporate the effects of inelastic transitions enabling an accurate description of the experimental differential cross section. The predictive power of our numerical results is benchmarked against empirical data of inelastic proton scattering off $^{12}$C, for the transition to the $2^+$ state at 4.44 MeV, in a range of projectile energies of 65-300 MeV. The generally good description of the experimental cross sections as functions of the scattering angle gives clear evidence of the reliability and robustness of a model that does not contain any free adjustable parameters.

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arXiv2025

Towards a microscopic description of nucleus-nucleus collisions

We present the first results of a comprehensive microscopic approach to describe nucleus-nucleus elastic collisions by means of an optical potential derived at first order in multiple-scattering theory and computed by folding the projectile and target nuclear densities with the nucleon-nucleon $t$ matrix, which describes the interaction between each nucleon of the projectile and each nucleon of the target. Chiral interactions are consistently used in the calculation of the $t$ matrix and of the nonlocal nuclear densities, which are computed within the ab initio no-core shell model. Cross sections calculated for $\alpha$ collisions on $^{12}$C and $^{16}$O at projectile energies in the range 100-300 MeV are presented and compared with available data. For momentum transfer $q$ up to about $1.0$ fm$^{-1}$ our results are in good agreement with the experimental data, whereas for higher momenta a reduction of the imaginary contributions is needed.

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arXiv2025

Measurement of the helicity-dependent response in quasi-elastic proton knockout from $^{40}{\rm Ca}$

The role of the electron-helicity-dependent cross-section term and the structure function $f^{\prime}_{01}$ in the quasi-elastic $A(\vec{e}, e^{\prime}p)$ process was studied. The $f^{\prime}_{01}$ was measured for proton knockout from the $1\mathrm{d}_{3/2}$ shell in $^{40}\mathrm{Ca}$ via the $^{40}{\rm Ca}(\vec{e},e' p)^{39}{\rm K}_{\rm g.s.}$ reaction, leaving the residual nucleus in a well-defined state. It requires a longitudinally polarized electron beam and out-of-plane proton detection. This structure function vanishes in the absence of final-state interactions (FSI) involving the ejected proton. Presented are the dependencies of $f^{\prime}_{01}$ on the missing momentum (closely related to the initial proton's Fermi momentum) and the angle between the knocked-out proton and the virtual photon momenta. The role of the spin-orbit interaction in FSI through the $\vec{L}\cdot \vec{S}$ term in a nuclear optical potential is discussed.

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arXiv2024

Determination of nuclear matter radii by means of microscopic optical potentials: the case of $^{78}$Kr

In this work we use microscopic Nucleon-Nucleus Optical Potentials (OP) to analyze elastic scattering data for the differential cross section of the $^{78}$Kr (p,p) $^{78}$Kr reaction, with the goal of extracting the matter radius and estimating the neutron skin, quantities that are both needed to determine the slope parameter $L$ of the nuclear symmetry energy. Our analysis is performed with the factorized version of the microscopic OP obtained in a previous series of papers within the Watson multiple scattering theory at the first order of the spectator expansion, which is based on the underlying nucleon-nucleon dynamics and is free from phenomenological inputs. Differently from our previous applications, the proton and neutron densities are described with a two-parameter Fermi (2pF) distribution, which makes the extraction of the matter radius easier and allows us to make a meaningful comparison with the original analysis, that was performed with the Glauber model. With standard minimization techniques we performed data analysis and extracted the matter radius and the neutron skin. Our analysis produces a matter radius of $R_m^{\rm (rms)} = 4.12$ fm, in good agreement with previous matter radii extracted from $^{76}$Kr and $^{80}$Kr, and a neutron skin of $ΔR_{np} \simeq - 0.1$ fm, compatible with a previous analysis. Our factorized microscopic OP, supplied with 2pF densities, is a valuable tool to perform the analysis of the experimental differential cross section and extract information such as matter radius and neutron skin. Without any free parameters it provides a reasonably good description of the experimental differential cross section for scattering angles up to $\approx$ 40 degrees. Compared to the Glauber model our OP can be applied to a wider range of scattering angles and allows one to probe the nuclear systems in a more internal region.

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arXiv2024

Microscopic optical potentials for medium-mass isotopes derived at the first order of the Watson multiple scattering theory

We perform a first-principle calculation of optical potentials for nucleon elastic scattering off medium-mass isotopes. Fully based on a saturating chiral Hamiltonian, the optical potentials are derived by folding nuclear density distributions computed with ab initio self-consistent Green's function theory with a nucleon-nucleon $t$ matrix computed with a consistent chiral interaction. The dependence on the folding interaction as well as the convergence of the target densities are investigated. Numerical results are presented and discussed for differential cross sections and analyzing powers, with focus on elastic proton scattering off Calcium and Nickel isotopes. Our optical potentials generally show a remarkable agreement with the available experimental data for laboratory energies in the range 65-200 MeV. We study the evolution of the scattering observables with increasing proton-neutron asymmetry by computing theoretical predictions of the cross section and analyzing power over the Calcium and Nickel isotopic chains.

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arXiv2023

Microscopic Optical Potentials from Chiral Forces and Ab Initio Nuclear Densities

We derived microscopic optical potentials (OPs) for elastic nucleon-nucleus scattering within the framework of chiral effective field theories at the first-order term of the spectator expansion of the Watson multiple-scattering theory and adopting the impulse approximation. Our OPs are derived by folding ab initio nuclear densities with a nucleon-nucleon NN t matrix computed with a consistent chiral interaction. The results of our OPs are in good agreement with the experimental data. Recent achievements of our work are reviewed in this contribution.

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arXiv2022

Elastic proton scattering off non-zero spin nuclei

In recent years, we constructed a microscopic optical potential (OP) for elastic nucleon-nucleus ($NA$) scattering using modern approaches based on chiral theories for the nucleon-nucleon ($NN$) interaction. The OP was derived at first order of the spectator expansion in Watson multiple scattering theory and its final expression was a folding integral between the $NN$ $t$ matrix and the nuclear density of the target. Two- and three-body forces are consistently included both in the target and in the projectile description. The purpose of this work is to apply our microscopic OP to nuclei characterized by a ground state of spin-parity quantum numbers $J^π\ne 0^+$. We extended our formalism to include the spin of the target nucleus. The full amplitudes of the $NN$ reaction matrix are retained in the calculations starting from two- and three-body chiral forces. We show a remarkable agreement with experimental data for the available observables and, simultaneously, provide reliable estimates for the theoretical uncertainties. This work paves the way toward a full microscopic approach to inelastic $NA$ scattering, showing that the derivation of optical potentials between states with $J^π\ne 0^+$ is completely under control.

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arXiv2021

Measurements of the electron-helicity asymmetry in the quasi-elastic ${\rm A}(\vec{e},e' p)$ process

We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from $^{2}$H and $^{12}$C nuclei by polarized electrons. This asymmetry depends on the fifth structure function, is antisymmetric with respect to the scattering plane, and vanishes in the absence of final-state interactions, and thus it provides a sensitive tool for their study. Our kinematics cover the full range in off-coplanarity angle $\phi_{pq}$, with a polar angle $\theta_{pq}$ coverage up to about 8 degrees. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual $^{11}$B system. We find that the helicity asymmetry for $p$-shell knockout from $^{12}$C depends on the final state of the residual system and is relatively large (up to $\approx 0.16$), especially at low missing momentum. It is considerably smaller (up to $\approx 0.01$) for $s$-shell knockout from both $^{12}$C and $^2$H. The data for $^2$H are in very good agreement with theoretical calculations, while the predictions for $^{12}$C exhibit differences with respect to the data.

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arXiv2020

Impact of Three-Body Forces on Elastic Nucleon-Nucleus Scattering Observables

In a previous series of papers we investigated the domain of applicability of chiral potentials to the construction of a microscopic optical potential (OP) for elastic nucleon-nucleus scattering. The final expression of the OP was a folding integral between the nucleon-nucleon ($NN$) $t$ matrix and the nuclear density of the target. In these calculations $NN$ and three-nucleon ($3N$) chiral interactions were used for the target density and only the $NN$ interaction for the $NN$ $t$ matrix. The purpose of this work is to achieve another step towards the calculation of a more consistent OP introducing the $3N$ force also in the dynamic part of the OP. In the present work this is approximated with a density dependent $NN$ interaction obtained after the averaging over the Fermi sphere. In practice, in our model the $3N$ force acts as a medium correction of the bare $NN$ interaction used to calculate the $NN$ $t$ matrix. Even if the $3N$ force is treated in an approximate way, this method naturally extends our previous model of the OP and allows a direct comparison of our present and previous results. We consider as case studies the elastic scattering of nucleons off $^{12}$C and $^{16}$O. We present results for the differential cross section and the spin observables for different values of the projectile energy. From the comparison with the experimental data and with the results of our previous model we assess the importance of the $3N$ interaction in the dynamic part of the OP. Our analysis indicates that the contribution of the $3N$ force in the $t$ matrix is small for the differential cross section and it is sizable for the spin observables, in particular, for the analyzing power. A chiral expansion order-by-order analysis of the scattering observables confirms the convergence of our results at the next-to-next-to-next-to-leading-order, as already established in our previous work.

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arXiv2020

Elastic Antiproton-Nucleus Scattering from Chiral Forces

Elastic scattering of antiprotons off $^4$He, $^{12}$C, and $^{16,18}$O is described for the first time with a totally microscopic approach based on the calculation of an optical potential (OP) describing the antiproton-target interaction. The OP is derived using the recent antiproton-nucleon ($\bar{p}N$) chiral interaction to calculate the $\bar{p}N$ $t$ matrix, while the target densities are computed with the ab initio no-core shell model using chiral interactions as well. Our results are in a good agreement with the existing experimental data and the results computed at different chiral orders of the $\bar{p}N$ interaction display the convergence pattern expected from the theory.

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arXiv2020

Measurements of the induced polarization in the quasi-elastic $A(e,e'\vec p\,)$ process in non-coplanar kinematics

We report measurements of the induced polarization $\vec P$ of protons knocked out from $^2$H and $^{12}$C via the $A(e,e'\vec p\,)$ reaction. We have studied the dependence of $\vec P$ on two kinematic variables: the missing momentum $p_{\rm miss}$ and the "off-coplanarity" angle $ϕ_{pq}$ between the scattering and reaction planes. For the full 360$\degree$ range in $ϕ_{pq}$, both the normal ($P_y$) and, for the first time, the transverse ($P_x$) components of the induced polarization were measured with respect to the coordinate system associated with the scattering plane. $P_x$ vanishes in coplanar kinematics, however in non-coplanar kinematics, it is on the same scale as $P_y$. We find that the dependence on $ϕ_{pq}$ is sine-like for $P_x$ and cosine-like for $P_y$. For carbon, the magnitude of the induced polarization is especially large when protons are knocked out from the $p_{3/2}$ shell at very small $p_{\rm miss}$. For the deuteron, the induced polarization is near zero at small $|p_{\rm miss}|$, and its magnitude increases with $|p_{\rm miss}|$. For both nuclei such behavior is reproduced qualitatively by theoretical results, driven largely by the spin-orbit part of the final-state interactions. However, for both nuclei, sizeable discrepancies exist between experiment and theory.

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arXiv2020

Polarization transfer to bound protons measured by quasi-elastic electron scattering on $^{12}$C

We report the measurements of the transverse ($P'x$) and longitudinal ($P'z$) components of the polarization transfer to a bound proton in carbon via the quasi-free $^{12}{\rm C}(\vec e,e'\vec p)$ reaction, over a wide range of missing momenta. We determine these polarization-transfers separately for protons knocked out from the $s$- and $p$-shells. The electron-beam polarization was measured to determine the individual components with systematic uncertainties which allow a detailed comparison with theoretical calculations.

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arXiv2019

Neutral Current Neutrino-Nucleus Scattering. Theory

The treatment of nuclear effects in neutrino-nucleus interactions is one of the main sources of systematic uncertainty for the analysis and interpretation of data of neutrino oscillation experiments. Neutrinos interact with nuclei via charged or neutral currents and both cases must be studied to obtain a complete information. We give an overview of the theoretical work that has been done to describe nuclear effects in neutral-current neutrin onucleus scattering in the kinematic region ranging between beam energies of a few hundreds MeV to a few GeV, which is typical of most ongoing and future accelerator-based neutrino experiments, and where quasielastic scattering is the main interaction mechanism. We review the current status and challenges of the theoretical models, the role and relevance of the contributions of different nuclear effects, and the present status of the comparison between the numerical predictions of the models as well as the available experimental data. We discuss also the sensitivity to the strange form factors of the nucleon and the methods and observables that can allow one to obtain evidence for a possible strange quark contribution from measurements of neutrino and antineutrino-nucleus scattering.

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arXiv2018

Proton-Nucleus Elastic Scattering: Comparison between Phenomenological and Microscopic Optical Potentials

Elastic scattering is a very important process to understand nuclear interactions in finite nuclei. Despite decades of efforts, the goal of reaching a coherent description of this physical process in terms of microscopic forces is still far from being completed. In previous papers (Phys. Rev. C93, 034619 (2016), Phys. Rev. C96, 044001 (2017)) we derived a nonrelativistic theoretical optical potential from nucleon-nucleon chiral potentials at fourth (N3LO) and fifth order (N4LO). We checked convergence patterns and established theoretical error bands. With this work we study the performances of our optical potential in comparison with those of a successful nonrelativistic phenomenological optical potential in the description of elastic proton scattering data on several isotopic chains at energies around and above 200 MeV. We use the same framework and the same approximations of our previous papers, where the nonrelativistic optical potential is derived at the first-order term within the spectator expansion of the multiple scattering theory and adopting the impulse approximation and the optimum factorization approximation. The cross sections and analyzing powers for elastic proton scattering off calcium, nickel, tin, and lead isotopes are presented for several incident proton energies, exploring the range $156 \le E \le 333$ MeV, where experimental data are available. In addition, we provide theoretical predictions for Ni56 at 400 MeV, which is of interest for the future experiments at EXL. Our results indicate that microscopic optical potentials derived from nucleon-nucleon chiral potentials at N4LO can provide reliable predictions for the cross section and the analyzing power both of stable and exotic nuclei, even at energies where the reliability of the chiral expansion starts to be questionable.

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arXiv2017

Exotic atoms at extremely high magnetic fields: the case of neutron star atmosphere

The presence of exotic states of matter in neutron stars (NSs) is currently an open issue in physics. The appearance of muons, kaons, hyperons, and other exotic particles in the inner regions of the NS, favored by energetic considerations, is considered to be an effective mechanism to soften the equation of state (EoS). In the so-called two-families scenario, the softening of the EoS allows for NSs characterized by very small radii, which become unstable and convert into a quark stars (QSs). In the process of conversion of a NS into a QS material can be ablated by neutrinos from the surface of the star. Not only neutron-rich nuclei, but also more exotic material, such as hypernuclei or deconfined quarks, could be ejected into the atmosphere. In the NS atmosphere, atoms like H, He, and C should exist, and attempts to model the NS thermal emission taking into account their presence, with spectra modified by the extreme magnetic fields, have been done. However, exotic atoms, like muonic hydrogen $(p\,μ^-)$ or the so-called Sigmium $(Σ^+\,e^-)$, could also be present during the conversion process or in its immediate aftermath. At present, analytical expressions of the wave functions and eigenvalues for these atoms have been calculated only for H. In this work, we extend the existing solutions and parametrizations to the exotic atoms $(p\,μ^-)$ and $(Σ^+\,e^-)$, making some predictions on possible transitions. Their detection in the spectra of NS would provide experimental evidence for the existence of hyperons in the interior of these stars.

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arXiv2017

From (e,e'p) to Neutrino Scattering

Since a long time electron scattering has been envisaged as a powerful and preferential tool to investigate nuclear properties. In particular, the (e,e'p) knockout reaction has provided a wealth of information on the single particle (s.p.) aspects of nuclear structure, on the validity and the limit of the independent particle shell model. The work done for electron scattering is extremely useful also for the analysis and the interpretation of neutrino oscillation experiments, where nuclei are used as neutrino detectors and it is crucial that nuclear effects in neutrino-nucleus interactions are well under control. In this contribution it is discussed if and how the work done for (e,e'p) can be exploited for the analysis of neutrino-nucleus scattering data.

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arXiv2017

Phenomenological and Theoretical Optical Potentials

The optical potential is a powerful instrument for calculations on a wide variety of nuclear reactions, in particular, for quasi-elastic lepton-nucleus scattering. Phenomenological optical potentials are successful in the description of data but may produce uncertainties in the interpretation of the results. Two recent theoretical optical potentials are presented: a global relativistic folding optical potential, that has been employed in relativistic models for quasi-elastic lepton-nucleus scattering, and a non relativistic optical potential derived from nucleon-nucleon chiral potentials at fourth order (N4LO), that has been applied to elastic proton-nucleus scattering.

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