arXiv subjects

A. Pastore

Publications and source records attributed to A. Pastore.

At least 37 records · Page 2Linked to original sources

arXiv2020

Generic size dependences of pairing in ultrasmall systems: electronic nano-devices and atomic nuclei

Average, global pairing behaviours of electronic devices, like films, wires, and grains are studied with semiclassical methods, as Weyl and Thomas-Fermi approximations, in the ultrasmall, i.e., quantal regime, which exhibits strong quantum fluctuations and shell effects. This is the case also for superfluid nuclei. Results, mostly analytic, are elaborated for average size dependences, ready for easy use also in other circumstances. Comparisons with experimental results are given where possible.

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arXiv2020

Finite-range separable pairing interaction in Cartesian coordinates

Within a simple SO(8) algebraic model, the coexistence between isoscalar and isovector pairing modes can be successfully described using a mean-field method plus restoration of broken symmetries. In order to port this methodology to real nuclei, we need to employ realistic density functionals in the pairing channel. In this article, we present an analytical derivation of matrix elements of a separable pairing interaction in Cartesian coordinates and we correct errors of derivations available in the literature. After implementing this interaction in the code hfodd, we study evolution of pairing gaps in the chain of deformed Erbium isotopes, and we compare the results with a standard density-dependent contact pairing interaction.

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arXiv2020

Neutron star matter equation of state including $d^*$-hexaquark degrees of freedom

We present an extension of a previous work where, assuming a simple free bosonic gas supplemented with a relativistic meand field model to describe the pure nucleonic part of the EoS, we studied the consequences that the first non-trivial hexaquark $d^*$(2380) could have on the properties of neutron stars. Compared to that exploratory work we employ a standard non-linear Walecka model including additional terms that describe the interaction of the $d^*(2380)$ di-baryon with the other particles of the system through the exchange of $σ$- and $ω$-meson fields. Our results have show that the presence of the $d^*(2380)$ leads to maximum masses compatible with the recent observations of $\sim 2$M$_\odot$ millisecond pulsars if the interaction of the $d^*(2380)$ is slightly repulsive or the $d^*(2380)$ does not interacts at all. An attractive interaction makes the equation of state too soft to be able to support a $2$M$_\odot$ neutron star whereas an extremely repulsive one induces the collapse of the neutron star into a black hole as soon as the $d^*(2380)$ appears.

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arXiv2020

Model nuclear energy density functionals derived from ab initio calculations

We present the first application of a new approach, proposed in [Journal of Physics G: Nuclear and Particle Physics, 43, 04LT01 (2016)] to derive coupling constants of the Skyrme energy density functional (EDF) from ab initio Hamiltonian. By perturbing the ab initio Hamiltonian with several functional generators defining the Skyrme EDF, we create a set of metadata that is then used to constrain the coupling constants of the functional. We use statistical analysis to obtain such an ab initio-equivalent Skyrme EDF. We find that the resulting functional describes properties of atomic nuclei and infinite nuclear matter quite poorly. This may point out to the necessity of building up the ab initio-equivalent functionals from more sophisticated generators. However, we also indicate that the current precision of the ab initio calculations may be insufficient for deriving meaningful nuclear EDFs.

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arXiv2019

Impact of statistical uncertainties on the composition of the outer crust of a neutron star

By means of Monte Carlo methods, we perform a full error analysis on the Duflo-Zucker mass model. In particular, we study the presence of correlations in the residuals to obtain a more realistic estimate of the error bars on the predicted binding energies. To further reduce the discrepancies between model prediction and experimental data we also apply a Multilayer Perceptron Neural Network. We show that the root mean square of the model further reduces of roughly 40\%. We then use the resulting models to predict the composition of the outer crust of a non accreting neutron star. We provide a first estimate of the impact of error propagation on the resulting equation of state of the system.

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arXiv2019

Linear response theory in asymmetric nuclear matter for Skyrme functionals including spin-orbit and tensor terms II: Charge Exchange

We present the formalism of linear response theory both at zero and finite temperature in the case of asymmetric nuclear matter excited by an isospin flip probe. The particle-hole interaction is derived from a general Skyrme functional that includes spin-orbit and tensor terms. Response functions are obtained by solving a closed algebraic system of equations. Spin strength functions are analyzed for typical values of density, momentum transfer, asymmetry and temperature.

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arXiv2019

Final results on neutrino oscillation parameters from the OPERA experiment in the CNGS beam

The OPERA experiment has conclusively observed the appearance of tau neutrinos in the muon neutrino CNGS beam. Exploiting the OPERA detector capabilities, it was possible to isolate high purity samples of $ν_{e}$, $ν_μ$ and $ν_τ$ charged current weak neutrino interactions, as well as neutral current weak interactions. In this Letter, the full dataset is used for the first time to test the three-flavor neutrino oscillation model and to derive constraints on the existence of a light sterile neutrino within the framework of the $3+1$ neutrino model. For the first time, tau and electron neutrino appearance channels are jointly used to test the sterile neutrino hypothesis. A significant fraction of the sterile neutrino parameter space allowed by LSND and MiniBooNE experiments is excluded at 90% C.L. In particular, the best-fit values obtained by MiniBooNE combining neutrino and antineutrino data are excluded at 3.3 $σ$ significance.

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arXiv2019

Electromagnetic properties of the $d^*(2380)$ hexaquark

Experiments with intense photon and electron beams have the potential to provide access to nontrivial properties of the recently discovered $d^*(2380)$ hexaquark including its size, structure, magnetic moment, quadrupole and octupole deformations. In this paper we investigate the sensitivity of ongoing and planned experiments to various properties of the $d^*(2380)$, employing models based on both constituent quark and pion cloud frameworks. Our calculations indicate that for photoinduced reactions on the deuteron the $d^*(2380)$ is predominantly produced from the $D-wave$ component of the deuteron. We confirm earlier findings that the intrinsic quadrupole deformation of the $d^*(2380)$ should be small. We also demonstrate an ability to extract the $d^*(2380)$ magnetic moment and put constrains on the $d^*(2380)$ $M3/E2$ ratio.

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arXiv2019

Symmetry restoration in the mean-field description of proton-neutron pairing

We show that the symmetry-restored paired mean-field states (quasiparticle vacua) properly account for isoscalar versus isovector nuclear pairing properties. Full particle-number, spin, and isospin symmetries are restored in a simple SO(8) proton-neutron pairing model, and prospects to implement a similar approach in a realistic setting are delineated. Our results show that, provided all symmetries are restored, the pictures based on pair-condensate and quartet-condensate wave functions represent equivalent ways of looking at the physics of nuclear proton-neutron pairing.

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arXiv2019

Shape staggering of mid-shell mercury isotopes from in-source laser spectroscopy compared with Density Functional Theory and Monte Carlo Shell Model calculations

Neutron-deficient $^{177-185}$Hg isotopes were studied using in-source laser resonance-ionization spectroscopy at the CERN-ISOLDE radioactive ion-beam facility, in an experiment combining different detection methods tailored to the studied isotopes. These include either alpha-decay tagging or Multi-reflection Time-of-Flight gating to identify the isotopes of interest. The endpoint of the odd-even nuclear shape staggering in mercury was observed directly by measuring for the first time the isotope shifts and hyperfine structures of $^{177-180}$Hg. Changes in the mean-square charge radii for all mentioned isotopes, magnetic dipole and electric quadrupole moments of the odd-A isotopes and arguments in favor of $I = 7/2$ spin assignment for $^{177,179}$Hg were deduced. Experimental results are compared with Density Functional Theory (DFT) and Monte-Carlo Shell Model (MCSM) calculations. DFT calculations with several Skyrme parameterizations predict a large jump in the charge radius around the neutron $N = 104$ mid shell, with an odd-even staggering pattern related to the coexistence of nearly-degenerate oblate and prolate minima. This near-degeneracy is highly sensitive to many aspects of the effective interaction, a fact that renders perfect agreement with experiment out of reach for current functionals. Despite this inherent diffculty, the SLy5s1 and a modified UNEDF1^{SO} parameterization predict a qualitatively correct staggering that is off by two neutron numbers. MCSM calculations of states with the experimental spins and parities show good agreement for both electromagnetic moments and the observed charge radii. A clear mechanism for the origin of shape staggering within this context is identified: a substantial change in occupancy of the proton $πh_{9/2}$ and neutron $νi_{13/2}$ orbitals.

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arXiv2019

An introduction to Bootstrap for nuclear physics

This guide aims at providing a general introduction to bootstrap methods. By using simple examples taken from nuclear physics, I discuss how such a method can be used to quantify error bars of an estimator. I also investigate the use of bootstrap to estimate parameters of a simple liquid drop model. In particular, I investigate how the method compares with standard techniques based on likelihood estimator and how to take into account correlations to better evaluate confidence interval of parameters.

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arXiv2018

Latest results of the OPERA experiment on nu-tau appearance in the CNGS neutrino beam

OPERA is a long-baseline experiment designed to search for $ν_μ\toν_τ$ oscillations in appearance mode. It was based at the INFN Gran Sasso laboratory (LNGS) and took data from 2008 to 2012 with the CNGS neutrino beam from CERN. After the discovery of $ν_τ$ appearance in 2015, with $5.1σ$ significance, the criteria to select $ν_τ$ candidates have been extended and a multivariate approach has been used for events identification. In this way the statistical uncertainty in the measurement of the oscillation parameters and of $ν_τ$ properties has been improved. Results are reported.

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arXiv2018

Advanced statistical methods to fit nuclear models

We discuss advanced statistical methods to improve parameter estimation of nuclear models. In particular, using the Liquid Drop Model for nuclear binding energies, we show that the area around the global $χ^2$ minimum can be efficiently identified using Gaussian Process Emulation. We also demonstrate how Markov-chain Monte-Carlo sampling is a valuable tool for visualising and analysing the associated multidimensional likelihood surface.

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arXiv2018

Error analysis of the parameters of the Skyrme N2LO pseudo-potential

We perform a detailed analysis of the parameters of the Skyrme SN2LO interaction. By mean of a covariance matrix analysis, we have been able to provide error bars and build the complete covariance matrix. The latter will be used in future applications to properly study the propagation of errors on nuclear observables calculated with this pseudo-potential.

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arXiv2018

Linear response theory for Gogny interaction

We present the formalism of the linear response theory in symmetric nuclear matter for a finite-range central interaction interaction including zero-range spin-orbit and tensor components.

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arXiv2018

Measurement of the cosmic ray muon flux seasonal variation with the OPERA detector

The OPERA experiment discovered muon neutrino into tau neutrino oscillations in appearance mode, detecting tau leptons by means of nuclear emulsion films. The apparatus was also endowed with electronic detectors with tracking capability, such as scintillator strips and resistive plate chambers. Because of its location, in the underground Gran Sasso laboratory, under 3800 m.w.e., the OPERA detector has also been used as an observatory for TeV muons produced by cosmic rays in the atmosphere. In this paper the measurement of the single muon flux modulation and of its correlation with the seasonal variation of the atmospheric temperature are reported.

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arXiv2018

Final results of the search for $ν_μ \to ν_{e}$ oscillations with the OPERA detector in the CNGS beam

The OPERA experiment has discovered the tau neutrino appearance in the CNGS muon neutrino beam, in agreement with the 3 neutrino flavour oscillation hypothesis. The OPERA neutrino interaction target, made of Emulsion Cloud Chamber, was particularly efficient in the reconstruction of electromagnetic showers. Moreover, thanks to the very high granularity of the emulsion films, showers induced by electrons can be distinguished from those induced by $π^0$s, thus allowing the detection of charged current interactions of electron neutrinos. In this paper the results of the search for electron neutrino events using the full dataset are reported. An improved method for the electron neutrino energy estimation is exploited. Data are compatible with the 3 neutrino flavour mixing model expectations and are used to set limits on the oscillation parameters of the 3+1 neutrino mixing model, in which an additional mass eigenstate $m_{4}$ is introduced. At high $Δm^{2}_{41}$ $( \gtrsim 0.1~\textrm{eV}^{2})$, an upper limit on $\sin^2 2θ_{μe}$ is set to 0.021 at 90% C.L. and $Δm^2_{41} \gtrsim 4 \times 10^{-3}~\textrm{eV}^{2}$ is excluded for maximal mixing in appearance mode.

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arXiv2018

Final results of the OPERA experiment on $ν_τ$ appearance in the CNGS beam

The OPERA experiment was designed to study $ν_μ\toν_τ$ oscillations in appearance mode in the CNGS neutrino beam. In this letter we report the final analysis of the full data sample collected between 2008 and 2012, corresponding to $17.97\cdot 10^{19}$ protons on target. Selection criteria looser than in previous analyses have produced ten $ν_τ$ candidate events, thus reducing the statistical uncertainty in the measurement of the oscillation parameters and of $ν_τ$ properties. A multivariate approach for event identification has been applied to the candidate events and the discovery of $ν_τ$ appearance is confirmed with an improved significance level of 6.1 $σ$. $Δm^2_{23}$ has been measured, in appearance mode, with an accuracy of 20%. The measurement of $ν_τ$ CC cross-section, for the first time with a negligible contamination from $\barν_τ$, and the first direct observation of the $ν_τ$ lepton number are also reported.

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