arXiv subjects

F. Cappuzzello

Publications and source records attributed to F. Cappuzzello.

35 records · Page 2Linked to original sources

arXiv2020

Nuclear structure studies performed using the (18O,16O) twoneutron transfer reactions

Excitation energy spectra and absolute cross section angular distributions were measured for the 13C(18O,16O)15C two-neutron transfer reaction at 84 MeV incident energy. This reaction selectively populates two-neutron configurations in the states of the residual nucleus. Exact finite-range coupled reaction channel calculations are used to analyse the data. Two approaches are discussed: the extreme cluster and the newly introduced microscopic cluster. The latter makes use of spectroscopic amplitudes in the centre of mass reference frame, derived from shell-model calculations using the Moshinsky transformation brackets. The results describe well the experimental cross section and highlight cluster configurations in the involved wave functions.

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arXiv2020

Charge-state distributions of 20Ne ions emerging from thin foils

New experimental measurements of charge state distributions produced by a 20Ne10+ beam at 15 MeV/u colliding on various thin solid targets are presented. The use of the MAGNEX magnetic spectrometer enabled measurements of the 8+ charge state down to fractions of a few 10-5. The use of different post-stripper foils located downstream of the main target is explored, showing that low Z materials are particularly effective to shift the charge state distributions towards fully stripped conditions. The dependence on the foil thickness is also studied and discussed.

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arXiv2020

NURE: An ERC project to study nuclear reactions for neutrinoless double beta decay

Neutrinoless double beta decay (0ν\b{eta}\b{eta}) is considered the best potential resource to determine the absolute neutrino mass scale. Moreover, if observed, it will signal that the total lepton number is not conserved and neutrinos are their own anti-particles. Presently, this physics case is one of the most important research beyond Standard Model and might guide the way towards a Grand Unified Theory of fundamental interactions. Since the \b{eta}\b{eta} decay process involves nuclei, its analysis necessarily implies nuclear structure issues. The 0ν\b{eta}\b{eta} decay rate can be expressed as a product of independent factors: the phase-space factors, the nuclear matrix elements (NME) and a function of the masses of the neutrino species. Thus the knowledge of the NME can give information on the neutrino mass scale, if the 0ν\b{eta}\b{eta} decay rate is measured. In the NURE project, supported by a Starting Grant of the European Research Council, nuclear reactions of double charge-exchange (DCE) will be used as a tool to extract information on the \b{eta}\b{eta} NME. In DCE reactions and \b{eta}\b{eta} decay, the initial and final nuclear states are the same and the transition operators have similar structure. Thus the measurement of the DCE absolute crosssections can give crucial information on \b{eta}\b{eta} matrix elements.

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arXiv2020

Measuring nuclear reaction cross sections to extract information on neutrinoless double beta decay

Neutrinoless double beta decay (0v\b{eta}\b{eta}) is considered the best potential resource to access the absolute neutrino mass scale. Moreover, if observed, it will signal that neutrinos are their own anti-particles (Majorana particles). Presently, this physics case is one of the most important research "beyond Standard Model" and might guide the way towards a Grand Unified Theory of fundamental interactions. Since the 0v\b{eta}\b{eta} decay process involves nuclei, its analysis necessarily implies nuclear structure issues. In the NURE project, supported by a Starting Grant of the European Research Council (ERC), nuclear reactions of double charge-exchange (DCE) are used as a tool to extract information on the 0v\b{eta}\b{eta} Nuclear Matrix Elements. In DCE reactions and \b{eta}\b{eta} decay indeed the initial and final nuclear states are the same and the transition operators have similar structure. Thus the measurement of the DCE absolute cross-sections can give crucial information on \b{eta}\b{eta} matrix elements. In a wider view, the NUMEN international collaboration plans a major upgrade of the INFN-LNS facilities in the next years in order to increase the experimental production of nuclei of at least two orders of magnitude, thus making feasible a systematic study of all the cases of interest as candidates for 0v\b{eta}\b{eta}.

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arXiv2019

Elastic and inelastic scattering of $^{16}$O on $^{27}$Al and $^{28}$Si at 240 MeV

The nuclear scattering at energies well above the Coulomb barrier allows for a fairly sensitive examination of the parameters of the optical potential when the relevant couplings are included into the calculations. In this work we present experimental angular distribution data for the elastic and inelastic scatterings of $^{16}$O impinging on $^{27}$Al and $^{28}$Si target nuclei at \textit{E}$_{lab}=240$ MeV. The experimental data were measured at $7\degree < θ_{c.m.} < 16\degree$ with good angular resolution. Experimental data are compared with coupled channel calculations with the inclusion of couplings to excited states in the target and projectile. We show that the shape of angular distributions are sensitive to the mass diffuseness parameter and the best agreement is achieved for $a = 0.62$ fm.

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arXiv2019

20Ne + 76Ge elastic and inelastic scattering at 306 MeV

Background: Double charge exchange (DCE) nuclear reactions have recently attracted much interest as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-beta decay. In this framework, a good description of the reaction mechanism and a complete knowledge of the initial and final-state interactions are mandatory. Presently, not enough is known about the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for future DCE studies. Among these, the 20Ne + 76Ge DCE reaction is particularly relevant due to its connection with 76Ge double-beta decay. Purpose: We intend to characterize the initial-state interaction for the 20Ne + 76Ge reactions at 306 MeV bombarding energy and determine the optical potential and the role of the couplings between elastic channel and inelastic transitions to the first low-lying excited states. Methods: We determine the experimental elastic and inelastic scattering cross-section angular distributions, compare the theoretical predictions by adopting different models of optical potentials with the experimental data, and evaluate the coupling effect through the comparison of the distorted-wave Born approximation calculations with the coupled channels ones. Results: Optical models fail to describe the elastic angular distribution above the grazing angle (9.4°). A correction in the geometry to effectively account for deformation of the involved nuclear systems improves the agreement up to about 14°. Coupled channels effects are crucial to obtain good agreement at large angles in the elastic scattering cross section.

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arXiv2019

Analysis of the one-neutron transfer to $^{16}$O, $^{28}$Si and $^{64}$Ni induced by ($^{18}$O, $^{17}$O) reaction at 84 MeV

Background: Recently, a systematic exploration of two-neutron transfer induced by the ($^{18}$O, $^{16}$O) reaction on different targets has been performed. The high resolution data have been collected at the MAGNEX magnetic spectrometer of the INFN-LNS laboratory in Catania and analyzed with the coupled reaction channel (CRC) approach. The simultaneous and sequential transfers of the two neutrons have been considered under the same theoretical framework without the need of adjustable factors in the calculations. Purpose: A detailed analysis of the one-neutron transfer cross sections is important to study the sequential two-neutron transfer. Here, we examine the ($^{18}$O, $^{17}$O) reaction on $^{16}$O, $^{28}$Si and $^{64}$Ni targets. These even-even nuclei allow for investigation of one-neutron transfer in distinct nuclear shell spaces. Method: The MAGNEX spectrometer was used to measure mass spectra of ejectiles and extract differential cross sections of one-neutron transfer to low-lying states. We adopted the same CRC formalism used in the sequential two-neutron transfer, including relevant channels and using spectroscopic amplitudes obtained from shell model calculations. We also compare with one-step distorted wave Born approximation (DWBA). Results: For the $^{18}$O + $^{16}$O and the $^{18}$O + $^{28}$O systems we used two interactions in the shell model. The experimental angular distributions are reasonably well reproduced by the CRC calculations. In the $^{18}$O + $^{64}$Ni system, we considered only one interaction and the theoretical curve describes the shape and order of magnitude observed in the experimental data. Conclusions: Comparisons between experimental, DWBA and CRC angle-integrated cross sections suggest that excitations before or after the transfer of neutron is relevant in the $^{18}$O + $^{16}$O and $^{18}$O + $^{64}$Ni systems.

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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).

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arXiv2018

Competition between direct and sequential two-neutron transfers in the $^{18}$O + $^{28}$Si collision at 84 MeV

In this work we study the simultaneous and sequential two-neutron transfer mechanisms to the $^{28}$Si nucleus induced by (t,p) and ($^{18}$O, $^{16}$O) reactions. New experimental cross sections for the $^{28}$Si($^{18}$O,$^{16}$O)$^{30}$Si reaction at 84 MeV are also presented. Direct reaction calculations are carried out within the Exact Finite Range Coupled Reaction Channel, for the simultaneous transfer of the two-neutron cluster, and the second order Distorted Wave Born Approximation, for the sequential transfer. Two different models are considered to describe the two-neutron cluster. The spectroscopic information was obtained from shell model calculation with {\it psdmod} interaction for the target overlaps where the 1p$_{3/2}$, 1p$_{1/2}$, 1d$_{3/2}$, 1d$_{5/2}$ and 2s$_{1/2}$ orbitals are included as valence sub-space. We show that simultaneous and sequential two-neutron transfer are competing mechanisms for the population of the ground state in $^{30}$Si. A systematic analysis of the two-neutron transfer induced by the ($^{18}O,^{16}O$) indicates that static deformation of target nuclei impacts on the two-neutron transfer mechanism.

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arXiv2018

The NUMEN project: NUclear Matrix Elements for Neutrinoless double beta decay

The article describes the main achievements of the NUMEN project together with an updated and detailed overview of the related R&D activities and theoretical developments. NUMEN proposes an innovative technique to access the nuclear matrix elements entering the expression of the lifetime of the double beta decay by cross section measurements of heavy-ion induced Double Charge Exchange (DCE) reactions. Despite the two processes, namely neutrinoless double beta decay and DCE reactions, are triggered by the weak and strong interaction respectively, important analogies are suggested. The basic point is the coincidence of the initial and final state many-body wave-functions in the two types of processes and the formal similarity of the transition operators. First experimental results obtained at the INFN-LNS laboratory for the 40Ca(18O,18Ne)40Ar reaction at 270 MeV, give encouraging indication on the capability of the proposed technique to access relevant quantitative information. The two major aspects for this project are the K800 Superconducting Cyclotron and MAGNEX spectrometer. The former is used for the acceleration of the required high resolution and low emittance heavy ion beams and the latter is the large acceptance magnetic spectrometer for the detection of the ejectiles. The use of the high-order trajectory reconstruction technique, implemented in MAGNEX, allows to reach the experimental resolution and sensitivity required for the accurate measurement of the DCE cross sections at forward angles. However, the tiny values of such cross sections and the resolution requirements demand beam intensities much larger than manageable with the present facility. The on-going upgrade of the INFN-LNS facilities in this perspective is part of the NUMEN project and will be discussed in the article.

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arXiv2018

Important role of projectile excitation in $^{16}$O+$^{60}$Ni and $^{16}$O+$^{27}$Al scattering at intermediate energies

The elastic scattering angular distribution of the $^{16}$O$+^{60}$Ni system at $260$ MeV was measured in the range of the Rutherford cross section down to $7$ orders of magnitude below. The cross sections of the lowest $2^{+}$ and $3^{-}$ inelastic states of the target were also measured over a several orders of magnitude range. Coupled channel (CC) calculations were performed and are shown to be compatible with the whole set of data only when including the excitation of the projectile and when the deformations of the imaginary part of the nuclear optical potential are taken into account. Similar results were obtained when the procedure is applied to the existing data on $^{16}$O$+^{27}$Al elastic and inelastic scattering at $100$ and $280$ MeV. An analysis in terms of Dynamical Polarization Potentials (DPP) indicate the major role of coupled channel effects in the overlapping surface region of the colliding nuclei.

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arXiv2017

Mini-phoswich and SiPM for Heavy Ion Detection

The possibility to use a mini-phoswich detector to identify ions in the region of Z ~ 10 is explored in the framework of the NUMEN project. The NUMEN program, aimed at the investigation of the nuclear matrix elements connected to the neutrinoless double beta decay by means of double charge exchange nuclear reactions, foresees very high fluencies, which prevent the use of standard silicon as stop detectors. The need of reasonable radiation hardness, together with a total energy resolution around 2% and a high granularity, makes scintillators possible candidates. Promising results are obtained using an array of plastic + inorganic phoswich scintillators readout by means of Silicon Photo Multipliers.

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arXiv2017

High precision probe of the fully sequential decay width of the Hoyle state in $^{12}$C

The decay path of the Hoyle state in $^{12}$C ($E_x=7.654\textrm{MeV}$) has been studied with the $^{14}\textrm{N}(\textrm{d},α_2)^{12}\textrm{C}(7.654)$ reaction induced at $10.5\textrm{MeV}$. High resolution invariant mass spectroscopy techniques have allowed to unambiguously disentangle direct and sequential decays of the state passing through the ground state of $^{8}$Be. Thanks to the almost total absence of background and the attained resolution, a fully sequential decay contribution to the width of the state has been observed. The direct decay width is negligible, with an upper limit of $0.043\%$ ($95\%$ C.L.). The precision of this result is about a factor $5$ higher than previous studies. This has significant implications on nuclear structure, as it provides constraints to $3$-$α$ cluster model calculations, where higher precision limits are needed.

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arXiv2016

The MAGNEX spectrometer: results and perspectives

This article discusses the main achievements and future perspectives of the MAGNEX spectrometer at the INFN-LNS laboratory in Catania (Italy). MAGNEX is a large acceptance magnetic spectrometer for the detection of the ions emitted in nuclear collisions below Fermi energy. In the first part of the paper an overview of the MAGNEX features is presented. The successful application to the precise reconstruction of the momentum vector, to the identification of the ion masses and to the determination of the transport efficiency is demonstrated by in-beam tests. In the second part, an overview of the most relevant scientific achievements is given. Results from nuclear elastic and inelastic scattering as well as from transfer and charge exchange reactions in a wide range of masses of the colliding systems and incident energies are shown. The role of MAGNEX in solving old and new puzzles in nuclear structure and direct reaction mechanisms is emphasized. One example is the recently observed signature of the long searched Giant Pairing Vibration. Finally, the new challenging opportunities to use MAGNEX for future experiments are briefly reported. In particular, the use of double charge exchange reactions toward the determination of the nuclear matrix elements entering in the expression of the half-life of neutrinoless double beta decay is discussed. The new NUMEN project of INFN, aiming at these investigations, is introduced. The challenges connected to the major technical upgrade required by the project in order to investigate rare processes under high fluxes of detected heavy ions are outlined.

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arXiv2015

Heavy-ion double charge exchange reactions: a tool towards 0v\b{eta}\b{eta} nuclear matrix elements

The knowledge of the nuclear matrix elements for the neutrinoless double beta decay is fundamental for neutrino physics. In this paper, an innovative technique to extract information on the nuclear matrix elements by measuring the cross section of a double charge exchange nuclear reaction is proposed. The basic point is that the initial and final state wave functions in the two processes are the same and the transition operators are similar. The double charge exchange cross sections can be factorized in a nuclear structure term containing the matrix elements and a nuclear reaction factor. First pioneering experimental results for the 40Ca(18O,18Ne)40Ar reaction at 270 MeV incident energy show that such cross section factorization reasonably holds for the crucial 0+ --> 0+ transition to 40Args, at least at very forward angles.

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arXiv2007

Study of the core-excited Fano Resonances in the neutron-rich C-isotopes

Fano Resonances are a new continuum excitation mode in light exotic nuclei. By the QPC model we explain these sharp and asymmetric structures as due to the coupling of a single particle elastic channel to the closed core-excited channels. Theoretical model calculations are compared for 15C, 17C and 19C. The theoretical results for 15C are in qualitative agreement with the experimental spectrum.

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arXiv2006

Core Excited Fano-Resonances in Exotic Nuclei

Fano-resonances are investigated as a new continuum excitation mode in exotic nuclei. By theoretical model calculations we show that the coupling of a single particle elastic channel to closed core-excited channels leads to sharp resonances in the low-energy continuum. A signature for such bound states embedded in the continuum (BSEC) are characteristic interference effects leading to asymmetric line shapes. Following the quasiparticle-core coupling model we consider the coupling of 1-QP (one-quasiparticle) and 3-QP components and find a number of long-living resonance structures close to the particle threshold. Results for 15C are compared with experimental data, showing that the experimentally observed spectral distribution and the interference pattern are in qualitative agreement with a BSEC interpretation.

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