arXiv subjects

S. Quaglioni

Publications and source records attributed to S. Quaglioni.

At least 19 recordsLinked to original sources

arXiv2026

ENDF/B-VIII.1: Updated Nuclear Reaction Data Library for Science and Applications

The ENDF/B-VIII.1 library is the newest recommended evaluated nuclear data file by the Cross Section Evaluation Working Group (CSEWG) for use in nuclear science and technology applications, and incorporates advances made in the six years since the release of ENDF/B-VIII.0. Among key advances made are that the $^{239}$Pu file was reevaluated by a joint international effort and that updated $^{16,18}$O, $^{19}$F, $^{28-30}$Si, $^{50-54}$Cr, $^{55}$Mn, $^{54,56,57}$Fe, $^{63,65}$Cu, $^{139}$La, $^{233,235,238}$U, and $^{240,241}$Pu neutron nuclear data from the IAEA coordinated INDEN collaboration were adopted. Over 60 neutron dosimetry cross sections were adopted from the IAEA's IRDFF-II library. In addition, the new library includes significant changes for $^3$He, $^6$Li,$^9$Be, $^{51}$V, $^{88}$Sr, $^{103}$Rh, $^{140,142}$Ce, Dy, $^{181}$Ta, Pt, $^{206-208}$Pb, and $^{234,236}$U neutron data, and new nuclear data for the photonuclear, charged-particle and atomic sublibraries. Numerous thermal neutron scattering kernels were reevaluated or provided for the very first time. On the covariance side, work was undertaken to introduce better uncertainty quantification standards and testing for nuclear data covariances. The significant effort to reevaluate important nuclides has reduced bias in the simulations of many integral experiments with particular progress noted for fluorine, copper, and stainless steel containing benchmarks. Data issues hindered the successful deployment of the previous ENDF/B-VIII.0 for commercial nuclear power applications in high burnup situations. These issues were addressed by improving the $^{238}$U and $^{239,240,241}$Pu evaluated data in the resonance region. The new library performance as a function of burnup is similar to the reference ENDF/B-VII.1 library. The ENDF/B-VIII.1 data are available in ENDF-6 and GNDS format at https://doi.org/10.11578/endf/2571019.

physics.app-ph↗

arXiv2024

Ab initio calculation of the $^3$He$(α,γ)^7$Be astrophysical S factor with chiral two- and three-nucleon forces

The $^3$He$(α,γ)^7$Be radiative capture reaction plays a key role in the creation of elements in stars as well as in the production of solar neutrinos, the observation of which is one of the main tools to study the properties of our sun. Since accurate experimental measurements of this fusion cross section at solar energies are difficult due to the strong Coulomb repulsion between the reactants, the onus falls on theory to provide a robust means for extrapolating from the region where experimental data is available down to the desired astrophysical regime. We present the first microscopic calculations of $^3$He$(α,γ)^7$Be with explicit inclusion of three-nucleon forces. Our prediction of the astrophysical $S$ factor qualitatively agrees with experimental data. We further incorporate experimental bound-state and scattering information in our calculation to arrive at a more quantitative description. This process reveals that our current model lacks sufficient repulsion in the $1/2^+$ channel of our model space to simultaneously reproduce elastic-scattering data. This deficit suggests that $^3$He$(α,γ)^7$Be probes aspects of the nuclear force that are not currently well-constrained.

nucl-th↗

arXiv2024

Ab initio investigation of the $^7$Li($p,e^+e^-$)$^8$Be process and the X17 boson

Observations of anomalies in the electron-positron angular correlations in high-energy decays in $^4$He, $^8$Be, and $^{12}$C have been reported recently by the ATOMKI collaboration. These could be explained by the creation and subsequent decay of a new boson with a mass of ${\sim}17$ MeV. Theoretical understanding of pair creation in the proton capture reactions used in these experiments is important for the interpretation of the anomalies. We apply the ab initio No-Core Shell Model with Continuum (NCSMC) to the proton capture on $^7$Li. The NCSMC describes both bound and unbound states in light nuclei in a unified way with chiral two- and three-nucleon interactions as the only input. We investigate the structure of $^8$Be, the $p+^7$Li elastic scattering, the $^7$Li($p,γ$)$^8$Be cross section and the internal pair creation $^7$Li($p,e^+ e^-$)$^8$Be. We discuss the impact of a proper treatment of the initial scattering state on the electron-positron angular correlation spectrum and compare our results to available ATOMKI data sets. Finally, we calculate $^7$Li($p,X$)$^8$Be cross sections for several proposed models of the hypothetical X17 particle.

nucl-th↗

arXiv2022

Ab initio investigations of A=8 nuclei: $α{-}α$ scattering, deformation in $^8$He, radiative capture of protons on $^7$Be and $^7$Li and the X17 boson

We apply the No-Core Shell Model with Continuum (NCSMC) that is capable of describing both bound and unbound states in light nuclei in a unified way with chiral two- and three-nucleon interactions as the only input. The NCSMC can predict structure and dynamics of light nuclei and, by comparing to available experimental data, test the quality of chiral nuclear forces. We discuss applications of NCSMC to the $α{-}α$ scattering and the structure of $^8$Be, the p+$^7$Be and p+$^7$Li radiative capture and the production of the hypothetical X17 boson claimed in ATOMKI experiments. The $^7$Be(p,$γ$)$^8$B reaction plays a role in Solar nucleosynthesis and Solar neutrino physics and has been subject of numerous experimental investigations. We also highlight our investigation of the neutron rich exotic $^8$He that has been recently studied experimentally at TRIUMF with an unexpected deformation reported.

nucl-th↗

arXiv2022

Ab initio calculation of the $β$-decay from $^{11}$Be to a p${+}^{10}$Be resonance

The exotic $β$-delayed proton emission is calculated in $^{11}$Be from first principles using chiral two- and three-nucleon forces. To investigate the unexpectedly-large branching ratio measured in [PRL 123, 082501 (2019)] we calculate the proposed $(1/2^+,1/2)$ proton resonance in $^{11}$B using the no-core shell model with continuum. This calculation helps to address whether this enhancement is caused by unknown dark decay modes or an unobserved proton resonance. We report a branching ratio of $b_p = (1.3\pm0.5)\times10^{-6}$, suggesting that its unexpectedly-large value is caused by an unobserved proton resonance in $^{11}$B.

nucl-th↗

arXiv2021

Quantum state preparation by adiabatic evolution with customized gates

Quantum state preparation by adiabatic evolution is currently rendered ineffective by the long implementation times of the underlying quantum circuits, comparable to the decoherence time of present and near-term quantum devices. These implementation times can be significantly reduced by realizing the evolution with a minimal number of customized gates. Employing a realistic model of a two-qubit processor, we carried out classical device-level simulations of the adiabatic evolution of a two-spin system implemented with customized two-qubit gates. These device-level simulations were compared with (experimental) ones solving the same problem on IBMQ systems. When used to emulate the IBMQ quantum circuit, our device-level simulations reached state fidelities ranging from 65% to 85%, similar to the actual performance of a diverse set of IBMQ devices.When we reduced the implementation time by using a minimal number of customized gates, however, the loss of fidelity was reduced by at least a factor of four, allowing us to accurately extract the energy of the target state. This improvement is enough to render adiabatic evolution useful for quantum state preparation for small systems or as a preconditioner for other state preparation methods.

quant-ph↗

arXiv2021

Proton inelastic scattering reveals deformation in $^8$He

A measurement of proton inelastic scattering of $^8$He at $8.25A$~MeV at TRIUMF shows a resonance at 3.54(6)~MeV with a width of 0.89(11)~MeV. The energy of the state is in good agreement with coupled cluster and no-core shell model with continuum calculations, with the latter successfully describing the measured resonance width as well. Its differential cross section analyzed with phenomenological collective excitation form factor and microscopic coupled reaction channels framework consistently reveals a large deformation parameter $β_2$ = 0.40(3), consistent with no-core shell model predictions of a large neutron deformation. This deformed double-closed shell at the neutron drip-line opens a new paradigm.

nucl-ex↗

arXiv2021

Using spin alignment of inelastically-excited fast beams to make spin assignments: the spectroscopy of 13O as a test case

Excited states in 13O were investigated using inelastic scattering of an E/A=69.5-MeV 13O beam off of a 9Be target. The excited states were identified in the invariant-mass spectra of the decay products. Both single proton and sequential two-proton decays of the excited states were examined. For a number of the excited states, the protons were emitted with strong anisotropy where emissions transverse to the beam axis are favored. The measured proton-decay angular distributions were compared to predictions from distorted-wave born-approximation (DWBA) calculations of the spin alignment which was shown to be largely independent of the excitation mechanism. The deduced $^{13}$O level scheme is compared to ab initio no-core shell model with continuum (NCSMC) predictions. The lowest-energy excited states decay isotropically consistent with predictions of strong proton 1s1/2 structure. Above these states in the level scheme, we observed a number of higher-spin states not predicted within the model. Possibly these are associated with rotational bands built on deformed cluster configurations predicted by antisymmetrized molecular dynamics (AMD) calculations. The spin alignment mechanism is shown to be useful for making spin assignments and may have widespread use.

nucl-ex↗

arXiv2021

Coupled-cluster calculations of neutrinoless double-beta decay in $^{48}$Ca

We use coupled-cluster theory and nuclear interactions from chiral effective field theory to compute the nuclear matrix element for the neutrinoless double-beta decay of $^{48}$Ca. Benchmarks with the no-core shell model in several light nuclei inform us about the accuracy of our approach. For $^{48}$Ca we find a relatively small matrix element. We also compute the nuclear matrix element for the two-neutrino double-beta decay of $^{48}$Ca with a quenching factor deduced from two-body currents in recent ab-initio calculation of the Ikeda sum-rule in $^{48}$Ca [Gysbers et al., Nature Physics 15, 428-431 (2019)].

nucl-th↗

arXiv2019

Application of an ab-initio S-matrix to data analysis of transfer to the continuum reactions populating 11Be

Recently, the bound and continuum spectrum of 11Be has been calculated within the ab-initio no-core shell model with continuum (NCSMC) method successfully reproducing the parity inversion in the ground state. The continuum spectrum obtained is in agreement with known experimental levels. The S-matrix contained in the NCSMC continuum wave functions of the n+10Be system is used in this work for the first time in a Transfer-to-the-Continuum (TC) reaction calculation. The TC approach is applied to study the excitation energy spectrum of 11Be measured in the 9Be(18O,16O)11Be reaction at 84 MeV. Previously known levels are confirmed and theoretical and experimental evidence for a 9/2+ state at Ex=5.8 MeV is given, whose configuration is thought to be 10Be(2+)+n(d5/2).

nucl-th↗

arXiv2019

Discrepancy between experimental and theoretical $β$-decay rates resolved from first principles

$β$-decay, a process that changes a neutron into a proton (and vice versa), is the dominant decay mode of atomic nuclei. This decay offers a unique window to physics beyond the standard model, and is at the heart of microphysical processes in stellar explosions and the synthesis of the elements in the Universe. For 50 years, a central puzzle has been that observed $β$-decay rates are systematically smaller than theoretical predictions. This was attributed to an apparent quenching of the fundamental coupling constant $g_A \simeq $ 1.27 in the nucleus by a factor of about 0.75 compared to the $β$-decay of a free neutron. The origin of this quenching is controversial and has so far eluded a first-principles theoretical understanding. Here we address this puzzle and show that this quenching arises to a large extent from the coupling of the weak force to two nucleons as well as from strong correlations in the nucleus. We present state-of-the-art computations of $β$-decays from light to heavy nuclei. Our results are consistent with experimental data, including the pioneering measurement for $^{100}$Sn. These theoretical advances are enabled by systematic effective field theories of the strong and weak interactions combined with powerful quantum many-body techniques. This work paves the way for systematic theoretical predictions for fundamental physics problems. These include the synthesis of heavy elements in neutron star mergers and the search for neutrino-less double-$β$-decay, where an analogous quenching puzzle is a major source of uncertainty in extracting the neutrino mass scale.

nucl-th↗

arXiv2017

The nuclear force imprints revealed on the elastic scattering of protons with $^{10}$C

How does nature hold together protons and neutrons to form the wide variety of complex nuclei in the universe? Describing many-nucleon systems from the fundamental theory of quantum chromodynamics has been the greatest challenge in answering this question. The chiral effective field theory description of the nuclear force now makes this possible but requires certain parameters that are not uniquely determined. Defining the nuclear force needs identification of observables sensitive to the different parametrizations. From a measurement of proton elastic scattering on $^{10}$C at TRIUMF and ab initio nuclear reaction calculations we show that the shape and magnitude of the measured differential cross section is strongly sensitive to the nuclear force prescription.

nucl-ex↗

arXiv2017

${}^{7}$Li($d$,$p$)${}^{8}$Li transfer reaction in the NCSM/RGM approach

Recently, we applied an $ab$ $initio$ method, the no-core shell model combined with the resonating group method, to the transfer reactions with light p-shell nuclei as targets and deuteron as the projectile. In particular, we studied the elastic scattering of deuterium on $^7$Li and the ${}^{7}$Li($d$,$p$)${}^{8}$Li transfer reaction starting from a realistic two-nucleon interaction. In this contribution, we review of our main results on the ${}^{7}$Li($d$,$p$)${}^{8}$Li transfer reaction, and we extend the study of the relevant reaction channels, by showing the dominant resonant phase shifts of the scattering matrix. We assess also the impact of the polarization effects of the deuteron below the breakup on the positive-parity resonant states in the reaction. For this purpose, we perform an analysis of the convergence trend of the phase and eigenphase shifts, with respect to the number of deuteron pseudostates included in the model space.

nucl-th↗

arXiv2015

Ab initio calculations of reactions with light nuclei

An {\em ab initio} (i.e., from first principles) theoretical framework capable of providing a unified description of the structure and low-energy reaction properties of light nuclei is desirable to further our understanding of the fundamental interactions among nucleons, and provide accurate predictions of crucial reaction rates for nuclear astrophysics, fusion-energy research, and other applications. In this contribution we review {\em ab initio} calculations for nucleon and deuterium scattering on light nuclei starting from chiral two- and three-body Hamiltonians, obtained within the framework of the {\em ab initio} no-core shell model with continuum. This is a unified approach to nuclear bound and scattering states, in which square-integrable energy eigenstates of the $A$-nucleon system are coupled to $(A-a)+a$ target-plus-projectile wave functions in the spirit of the resonating group method to obtain an efficient description of the many-body nuclear dynamics both at short and medium distances and at long ranges.

nucl-th↗

arXiv2013

Three-cluster dynamics within an ab initio framework

We introduce a fully antisymmetrized treatment of three-cluster dynamics within the ab initio framework of the no-core shell model/resonating-group method (NCSM/RGM). Energy-independent non-local interactions among the three nuclear fragments are obtained from realistic nucleon-nucleon interactions and consistent ab initio many-body wave functions of the clusters. The three-cluster Schrödinger equation is solved with bound-state boundary conditions by means of the hyperspherical-harmonic method on a Lagrange mesh. We discuss the formalism in detail and give algebraic expressions for systems of two single nucleons plus a nucleus. Using a soft similarity-renormalization-group evolved chiral nucleon-nucleon potential, we apply the method to an $^4$He+$n+n$ description of $^6$He and compare the results to experiment and to a six-body diagonalization of the Hamiltonian performed within the harmonic-oscillator expansions of the NCSM. Differences between the two calculations provide a measure of core ($^4$He) polarization effects.

nucl-th↗

arXiv2012

From nucleons to nuclei to fusion reactions

Nuclei are prototypes of many-body open quantum systems. Complex aggregates of protons and neutrons that interact through forces arising from quantum chromo-dynamics, nuclei exhibit both bound and unbound states, which can be strongly coupled. In this respect, one of the major challenges for computational nuclear physics, is to provide a unified description of structural and reaction properties of nuclei that is based on the fundamental underlying physics: the constituent nucleons and the realistic interactions among them. This requires a combination of innovative theoretical approaches and high-performance computing. In this contribution, we present one of such promising techniques, the ab initio no-core shell model/resonating-group method, and discuss applications to light nuclei scattering and fusion reactions that power stars and Earth-base fusion facilities.

nucl-th↗

arXiv2009

Electric Dipole Polarizabilities of Hydrogen and Helium Isotopes

The electric dipole polarizabilities of $^3$H, $^3$He, and $^4$He are calculated directly using the Schrödinger equation with the latest generation of two- and three-nucleon interactions. These polarizabilities are necessary in order to obtain accurate nuclear-polarization corrections for transitions involving S-waves in one- and two-electron atoms. Our results are compared to previous results, and it is shown that direct calculations of the electric polarizability of $^4$He using modern nuclear potentials are smaller than published values calculated using experimental photoabsorption data. The status of this topic is assessed in the context of precise measurements of transitions in one- and two-electron atoms.

nucl-th↗

arXiv2009

The ab initio no-core shell model

This contribution reviews a number of applications of the ab initio no-core shell model (NCSM) within nuclear physics and beyond. We will highlight a nuclear-structure study of the A = 12 isobar using a chiral NN + 3NF interaction. In the spirit of this workshop we will also mention the new development of the NCSM formalism to describe open channels and to approach the problem of nuclear reactions. Finally, we will illustrate the universality of the many-body problem by presenting the recent adaptation of the NCSM effective-interaction approach to study the many-boson problem in an external trapping potential with short-range interactions.

nucl-th↗