Background estimate in heavy-ion two-body reactions measured by the MAGNEX spectrometer

The MAGNEX magnetic spectrometer is nowadays used in the experimental measurements of rare quasi-elastic reactions between heavy ions at intermediate energy within the NUMEN project. The small cross sections involved in such processes under the large yields due to competitive reaction channels have motivated an accurate control of the background sources. In such view, the not ideal particle identification could introduce spurious contributions which have been identified and evaluated in the present analysis

One-neutron transfer reaction in the 18^{18}O + 48^{48}Ti collision at 275 MeV

The present article reports new data on the $^{48}$Ti($^{18}$O,$^{17}$O)$^{49}$Ti reaction at 275 MeV incident energy as part of the systematic research pursued within the NUMEN project. Supplementary measurements of the same reaction on $^{16}$O and $^{27}$Al targets were also performed in order to estimate the background arising from the use of a composite target (TiO$_{2}$ + $^{27}$Al). These data were analyzed under the same theoretical framework as those obtained with the titanium target in order to reinforce the conclusions of our analysis. Differential cross-section angular distribution measurements for the $^{17}$O$^{8+}$ ejectiles were performed in a wide angular range by using the MAGNEX large acceptance magnetic spectrometer. The experimental results were analyzed within the distorted-wave and coupled-channels Born Approximation frameworks. The optical potentials at the entrance and exit channels were calculated in a double folding approach adopting the S\~ao Paulo potential, and the spectroscopic amplitudes for the projectile and target overlaps were obtained from large-scale shell model calculations. The differential cross-sections are well-described by the theoretical calculations, where a weak coupling to collective excitations of projectile and target is inferred. The sensitivity of transfer cross-sections on different model spaces adopted in nuclear structure calculations, is also discussed

One-proton transfer reaction for the O 18 + Ti 48 system at 275 MeV

Single-nucleon transfer reactions are processes that selectively probe single-particle components of the populated many-body nuclear states. In this context, recent efforts have been made to build a unified description of the rich nuclear spectroscopy accessible in heavy-ion collisions. An example of this multichannel approach is the study of the competition between successive nucleon transfer and charge exchange reactions, the latter being of particular interest in the context of single and double beta decay studies. To this extent, the one-proton pickup reaction Ti48(O18,F19)Sc47 at 275 MeV was measured for the first time, under the NUMEN experimental campaign. Differential cross-section angular distribution measurements for the F19 ejectiles were performed at INFN-LNS in Catania by using the MAGNEX large acceptance magnetic spectrometer. The data were analyzed within the distorted-wave and coupled-channels Born approximation frameworks. The initial and final-state interactions were described adopting the São Paulo potential, whereas the spectroscopic amplitudes for the projectile and target overlaps were derived from shell-model calculations. The theoretical cross sections are found to be in very good agreement with the experimental data, suggesting the validity of the optical potentials and the shell-model description of the involved nuclear states within the adopted model space

Experimental challenges for the measurement of the116Cd(20Ne,20O)116Sn double charge exchange reaction at 15 AMeV

The knowledge of the nuclear matrix elements (NME) entering in the expression of the half-life of the neutrinoless double beta decay is fundamental for neutrino physics . Information on the nuclear matrix elements can be obtained by measuring the absolute cross section of double charge exchange nuclear reactions. The two processes present some similarities, the initial and final-state wave functions are the same and the transition operators are similar. The experimental measurements of double charge exchange reactions induced by heavy ions present a number of challenging aspects, since such reactions are characterized by very low cross sections. Such difficulties are discussed for the measurement of the 116Cd(20Ne,20O)116Sn reaction at 15 AMeV

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

The article describes the main achievements of the NUMEN project togetherwith an updated and detailed overview of the related R&D activities andtheoretical developments. NUMEN proposes an innovative technique to access thenuclear matrix elements entering the expression of the lifetime of the doublebeta decay by cross section measurements of heavy-ion induced Double ChargeExchange (DCE) reactions. Despite the two processes, namely neutrinoless doublebeta decay and DCE reactions, are triggered by the weak and strong interactionrespectively, important analogies are suggested. The basic point is thecoincidence of the initial and final state many-body wave-functions in the twotypes of processes and the formal similarity of the transition operators. Firstexperimental results obtained at the INFN-LNS laboratory for the40Ca(18O,18Ne)40Ar reaction at 270 MeV, give encouraging indication on thecapability of the proposed technique to access relevant quantitativeinformation. The two major aspects for this project are the K800Superconducting Cyclotron and MAGNEX spectrometer. The former is used for theacceleration of the required high resolution and low emittance heavy ion beamsand the latter is the large acceptance magnetic spectrometer for the detectionof the ejectiles. The use of the high-order trajectory reconstructiontechnique, implemented in MAGNEX, allows to reach the experimental resolutionand sensitivity required for the accurate measurement of the DCE cross sectionsat forward angles. However, the tiny values of such cross sections and theresolution requirements demand beam intensities much larger than manageablewith the present facility. The on-going upgrade of the INFN-LNS facilities inthis perspective is part of the NUMEN project and will be discussed in thearticle

A constrained analysis of the 40Ca(18O,18F)40K direct charge exchange reaction mechanism at 275 Mev

The40 Ca(18 O,18 F)40 K single charge exchange (SCE) reaction is explored at an incident energy of 275 MeV and analyzed consistently by collecting the elastic scattering and inelastic scattering data under the same experimental conditions. Full quantum-mechanical SCE calculations of the direct mechanism are performed by including microscopic nuclear structure inputs and adopting either a bare optical potential or a coupled channel equivalent polarization potential (CCEP) constrained by the elastic and inelastic data. The direct SCE mechanism describes the magnitude and shape of the angular distributions rather well, thus suggesting the suppression of sequential multi-nucleon transfer processes