A multi–channel study of the 20^{20}Ne + 130^{130}Te system within the NUMEN project

International audienceThe NUMEN project aims to measure specific reaction cross sections to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double beta decay (0νββ). In particular, it was proposed to use heavy – ion induced double charge exchange reactions as tools towards the determination of information on the nuclear matrix elements of 0νββ, strongly motivated by a number of similarities between the two processes. To this extent, the $^{20}$Ne + $^{130}$Te system was experimentally investigated in a multi-channel approach by measuring the complete net of reactions channels, namely double charge exchange, single charge exchange, elastic and inelastic scattering, one – and two – nucleon transfer reactions, characterized by the same initial projectile and target nuclei. The goal of the study is to fully characterize the properties of the nuclear wavefunctions entering in the 0νββ decay nuclear matrix elements. The experimental setup, the data reduction and some of the obtained results for the $^{20}$Ne + $^{130}$Te system will be presented and discussed

The NUMEN Project: An Update of the Facility Toward the Future Experimental Campaigns

International audienceThe goal of NUMEN project is to access experimentally driven information on Nuclear Matrix Elements (NME) involved in the neutrinoless double beta decay (0νββ) by accurate measurements of the cross sections of heavy-ion induced double charge-exchange reactions. In particular, the (18O, 18Ne) and (20Ne, 20O) reactions are adopted as tools for β+β+ and β-β- decays, respectively. The experiments are performed at INFN - Laboratory Nazionali del Sud (LNS) in Catania using the Superconducting Cyclotron to accelerate the beams and the MAGNEX magnetic spectrometer to detect the reaction products. The measured cross sections are very low, limiting the present exploration to few selected isotopes of interest in the context of typically low-yield experimental runs. In order to make feasible a systematic study of all the candidate nuclei, a major upgrade of the LNS facility is foreseen to increase the experimental yield by more than two orders of magnitude. To this purpose, frontier technologies are being developed for both the accelerator and the detection systems. An update description of the NUMEN project is presented here, focusing on recent achievements from the R&D activity

Data reduction for experimental measurements within the NUMEN project

International audienceWithin the NUMEN project, we present experimental issues and data reduction for the 116Cd(20Ne,20F)116In single charge exchange, 116Cd(20Ne,18O)118In two-proton transfer and 116Cd(20Ne,19F)117In one-proton transfer reactions at 15 AMeV incident energy

Heavy–ion particle identification for the transfer reaction channels for the system 18^{18}O + 116^{116}Sn under the NUMEN Project

International audienceThe current work is a part of the NUMEN project, which aims to deduce the nuclear matrix elements (NME) of neutrinoless double beta decay by measuring the cross sections in heavy-ion induced Double Charge Exchange (DCE) reactions. The particle identification for the competing transfer reaction channels has been studied for the 18O + 116Sn system at 270 MeV

Experimental and theoretical multi-channel study of direct nuclear reactions: a tool to provide data driven information on the 76^{76}Ge neutrino-less double-beta decay

International audienceThe study of heavy-ions induced double charge-exchange (HI-DCE) nuclear reactions is a promising way to access data-driven information on neutrino-less double-beta decay nuclear matrix elements. In the following, particular attention is given to the ($^{18}$O,$^{18}$Ne) and ($^{20}$Ne,$^{20}$O) HI-DCE reactions as tools for β$^{+}$β$^{+}$ and β$^{−}$β$^{−}$ decays, respectively. The experiments are performed in Catania at the Laboratori Nazionali del Sud of the Istituto Nazionale di Fisica Nucleare (INFN-LNS). The MAGNEX magnetic spectrometer is used to momentum analyse the ejectiles of a large network of nuclear reactions. New preliminary experimental data for the $^{76}$Se($^{18}$O,$^{18}$F)$^{76}$As and $^{76}$Ge($^{20}$Ne,$^{20}$F)$^{76}$As single charge exchange (SCE) and for the $^{76}$Se($^{18}$O,$^{18}$Ne)$^{76}$Ge and $^{76}$Ge($^{20}$Ne,$^{20}$O)$^{76}$Se DCE nuclear reactions were also investigated

Initial state interaction for the20 ne +130 te and18 o +116 sn systems at 15.3 amev from elastic and inelastic scattering measurements

Double charge exchange (DCE) reactions could provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To achieve this goal, a detailed description of the reaction mechanism is mandatory. This requires the full characterization of the initial and final-state interactions, which are poorly known for many of the projectile-target systems involved in future DCE studies. Among these, we intend to study the20 Ne +130 Te and18 O +116 Sn systems at 15.3 AMeV, which are particularly relevant due to their connection with the130 Te→130 Xe and116 Cd→116 Sn double-β decays. We measure the elastic and inelastic scattering cross-section angular distributions and compare them with theoretical calculations performed in the optical model, one-step distorted wave Born approximation, and coupled-channel approaches using the São Paulo double-folding optical potential. A good description of the experimental data in the whole explored range of transferred momenta is obtained provided that couplings with the 2+1 states of the projectile and target are explicitly included within the coupled-channel approach. These results are relevant also in the analysis of other quasi-elastic reaction channels in these systems, in which the same couplings should be included. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Analysis of the background on cross section measurements with the MAGNEX spectrometer: The (20Ne, 20O) Double Charge Exchange case

The MAGNEX magnetic spectrometer is used in the experimental measurements of Double Charge Exchange and Multi-Nucleon Transfer reactions induced by heavy ions within the NUMEN project. These processes are characterized by small cross sections under a large background due to other reaction channels. Therefore an accurate control of the signal to background ratio is mandatory. In this article, the determination of the MAGNEX spectrometer background contribution on cross section measurements is presented by applying a suitable analysis to quantify the limits of the adopted particle identification technique. The method is discussed considering the 116Cd(20Ne, 20O)116Sn Double Charge Exchange reaction data, however it can be applied to any other reaction channel of interest. © 2020 Elsevier B.V

Analysis of one-proton transfer reaction in <math><mrow><mmultiscripts><mi mathvariant="normal">O</mi><mprescripts/><none/><mn>18</mn></mmultiscripts><mo>+</mo><mmultiscripts><mi>Se</mi><mprescripts/><none/><mn>76</mn></mmultiscripts></mrow></math> collisions at 275 MeV

International audienceBackground: A systematic exploration of one-nucleon transfer reactions induced by the (O18,F19) and (O18,O17) reactions on different targets (C12, O16, Al27, Ca40, Ti48, Se76, Sn116) is being performed at the Istituto Nazionale di Fisica Nucleare–Laboratori Nazionali del Sud (INFN-LNS) at beam energies higher than Coulomb barrier. A featured aspect is the adoption of a multichannel reaction approach, where several quasielastic processes are studied consistently from both the experiment and theory sides. Resembling the case of light-ion induced direct reactions, for which a large amount of data exists, the multichannel heavy-ion direct reaction is a powerful tool to characterize nuclear mean field as well as few-nucleon correlations in low-lying nuclear states. In this view, the study of different reaction mechanisms and nuclear structure models helps to characterize the nuclear wave functions and accurately scrutinize the parameters that control the uncertainties in the calculations of nuclear matrix elements (NMEs). In this context, special attention is recently paid to NMEs involved in second-order isotensor processes such as double charge exchange (DCE) and neutrinoless double beta (0νββ) decay.Purpose: We perform the experiment and the data analysis based on theoretical models of one-nucleon transfer reactions induced by the O18+Se76 collision at energies above the Coulomb barrier in a multichannel approach. The Se76 nucleus attracts nowadays much interest since it is the daughter in the Ge76 ββ decay, and the nuclear matrix elements involved in the Seg.s.76→Geg.s.76 and Geg.s.76→Seg.s.76 transitions are the same for time reversal symmetry. In particular, we intend to analyze transitions to low-lying excited states of the residual and ejectile nuclei in the Se76(O18,F19)As75 one-proton pickup reaction at 275 MeV incident energy by measuring the cross section. An additional goal is to determine the role of the coupling channels in the measured cross sections, testing different model descriptions of the involved nuclear states.Methods: Nuclear reactions induced by the O18+Se76 collision were measured at INFN-LNS using the MAGNEX large acceptance magnetic spectrometer for the detection of the ejectiles. The missing mass technique was used for the reconstruction of the reaction kinematics. The excitation energy spectrum and the differential cross section angular distributions were the key extracted observables. The experimental data were compared with theoretical calculations based on the distorted wave Born approximation, the coupled-channels Born approximation, and coupled reaction channels. The adopted spectroscopic amplitudes for the projectile and target overlaps were derived by large-scale shell-model and interacting boson-fermion model calculations. In the calculations the initial state interaction and the nuclear structure model inputs were the same as those adopted in the study of elastic and inelastic scattering and (O18,O17) one-neutron stripping reaction, published elsewhere.Results: Peaks in the cross section energy spectra corresponding to groups of transitions to As75 and F19 were identified and the experimental angular distributions were compared with theoretical calculations. A fair agreement between theory and experiment both in cross section values and diffraction pattern is obtained, without the need for any scaling factor, validating the adopted reaction and nuclear structure approaches.Conclusions: Resembling the case of the (O18,O17) one-neutron stripping reaction, the couplings to the inelastic channels of projectile and target are significant for the one-proton pickup reaction and are likely to also play a role in the single and double charge exchange reactions. The fair description of the data is remarkable since no free parameter was used for this analysis, highlighting that the multichannel approach guarantees an accurate investigation of all the interesting reactions induced by the O18+Se76 collision

Multichannel experimental and theoretical constraints for the 116Cd(20Ne,20F)116In^{116}\mathrm{Cd}(^{20}\mathrm{Ne},^{20}\mathrm{F})^{116}\mathrm{In} charge exchange reaction at 306 MeV

International audienceBackground: Charge-exchange (CE) reactions offer a major opportunity to excite nuclear isovector modes, providing important clues about the nuclear interaction in the medium. Moreover, double charge-exchange reactions are proving to be a tempting tool to access nuclear transition matrix elements (NMEs) related to double beta-decay processes. The latter are also of crucial importance to extract neutrino properties from the half-life of the hypothetical neutrinoless double beta decay and to search for physics beyond the standard model.Purpose: Through a multichannel experimental analysis and a consistent theoretical approach of the Cd116(Ne20,F20)In116 single charge-exchange (SCE) reaction at 306 MeV, we aim at disentangling from the experimental cross section the contribution of the competing mechanisms associated with second- or higher-order sequential transfer and/or inelastic processes.Methods: We measured excitation energy spectra and absolute cross sections for elastic + inelastic, one-proton transfer and SCE channels by using the MAGNEX large acceptance magnetic spectrometer to detect the ejectiles. For the first two channels, we also extracted the experimental cross-section angular distributions. The experimental data are compared with theoretical predictions obtained by performing two-step distorted-wave Born approximation and coupled reaction channel calculations. We employ spectroscopic amplitudes for single-particle transitions derived within a large-scale shell-model approach and different optical potentials for modeling the initial- and the final-state interactions.Results: The present study significantly mitigates the possible model dependence existing in the description of these complex reaction mechanisms thanks to the satisfactory reproduction of several channels at once. In particular, our work demonstrates that the two-step transfer mechanisms produce a non-negligible contribution to the total cross section of the Cd116(Ne20,F20)In116 reaction channel, although a relevant fraction is still missing, being ascribable to the direct SCE mechanism, which is not addressed here.Conclusions: Our analysis provides a careful estimation of the sequential transfer processes which are competing with the direct SCE mechanism for the heavy ion reaction under investigation. The study suggests that the direct SCE should play an important role among the mechanisms populating the final channel. Nevertheless, the analysis of the higher-order processes considered here is mandatory to isolate the direct SCE process contribution and approach structure information on the corresponding NME from the reaction cross section. The description of the latter process and the competition between the two mechanisms deserves further investigation