Double Charge Exchange Research Articles

A mini-phoswich scintillator as a possible stop detector for the NUMEN project

In the framework of the NUMEN project, aimed at the investigation of the nuclear matrix elements connected to the neutrinoless double beta decay by means of the Double Charge Exchange nuclear reactions (Cappuzzello et al., 2015), a high granularity stop detector for heavy ions is needed. It has to allow the identification of ions up to Z≈10 while maintaining a total energy resolution around 2%. As the use of silicon detectors is not possible, due to their poor radiation hardness, scintillators are being investigated as possible candidates. In this paper we show a promising result obtained using a plastic+inorganic phoswich scintillator readout by means of a Silicon Photo Multiplier.

Heavy-ion double charge exchange reactions: A tool toward $0 \nu\beta\beta$ 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.

Heavy Ions Double Charge Exchange reactions: towards the 0νββ Nuclear Matrix Element determination

First experimental results, obtained at the INFN-LNS laboratory in Catania, for the 40Ca(18O,18Ne)40Ar reaction at 270 MeV are shown. The data give encouraging indication on the capability to access quantitative information towards the determination of the Nuclear Matrix Elements for 0νββ decay. The idea is to use an innovative technique to access the nuclear matrix elements entering the expression of the life time of the double beta decay by cross sections measurements of double charge exchange reactions. The basic point is the coincidence of the initial and final state wave-functions in the two classes of processes and the similarity of the transition operators, which in both cases present a superposition of Fermi-like, Gamow-Teller-like and rank-two tensor components with a relevant implicit momentum available in the intermediate channel.

Charge exchange in cometary coma: Discovery of H- ions in the solar wind close to comet 67P/Churyumov-Gerasimenko.

As Rosetta was orbiting comet 67P/Churyumov‐Gerasimenko, the Ion and Electron Sensor detected negative particles with angular distributions like those of the concurrently measured solar wind protons but with fluxes of only about 10% of the proton fluxes and energies of about 90% of the proton energies. Using well‐known cross sections and energy‐loss data, it is determined that the fluxes and energies of the negative particles are consistent with the production of H− ions in the solar wind by double charge exchange with molecules in the coma.

The role of nuclear reactions in the problem of 0νββ decay and the NUMEN project at INFN-LNS

An innovative technique to access the nuclear matrix elements entering the expression of the life time of the double beta decay by relevant cross sections of double charge exchange reactions is proposed. The basic point is the coincidence of the initial and final state wave-functions in the two classes of processes and the similarity of the transition operators, which in both cases present a superposition of Fermi, Gamow-Teller and rank-two tensor components with a relevant implicit momentum transfer. First pioneering 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. A key aspect of the project is the use of the K800 Superconducting Cyclotron (CS) for the acceleration of the required high resolution and low emittance heavy- ion beams and of the MAGNEX 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 high mass, angular and energy resolution required even at very low cross section. The LNS set-up is today an ideal one for this research even in a worldwide perspective. However a main limitation on the beam current delivered by the accelerator and the maximum rate accepted by the MAGNEX focal plane detector must be sensibly overcome in order to systematically provide accurate numbers to the neutrino physics community in all the studied cases. The upgrade of the LNS facilities in this view is part of this project.

Double-electron capture in collision of fast alpha particles with helium atoms

A four-body boundary-corrected first-order Jackson–Schiff approximation (JS1-4B) is developed to calculate the differential and integral cross-sections (DCSs) for double-electron exchange in collision of fast alpha ions with helium atoms in their ground states. The influence of the static electron correlations on cross-sections is taken into account through choosing the different wave functions to describe the initial and final bound states of the electrons. The quantum-mechanical post and prior transition amplitudes for double charge exchange are derived in terms of two-dimensional real integrals which can be calculated numerically. The validity and utility of the applied approach is critically assessed in comparison with the available experimental data for differential and integral cross-sections. The present calculations are also compared with the results obtained from the other theories.

Precision spectroscopy of trapped highly charged heavy elements: pushing the limits of theory and experiment

Atomic spectroscopy results from the electron beam ion trap at the National Institute of Standards and Technology have generally agreed with the predictions of theory extremely well. An interesting exception is our recent result on the helium isoelectronic sequence at Z = 22, which agrees instead with a meta-analysis of all prior measurements above Z = 15, but disagrees with both theory and a contemporaneous report of an independent measurement at Z = 18 which claims to validate theory to high accuracy. Here, a potential systematic shift involving high-n satellite lines induced by double charge exchange is quantitatively estimated and shown to be potentially significant in experiments involving gasses. Suggestions for further refinements in estimating the magnitude of this systematic shift are given.

Astatine production in a lead-bismuth target bombarded by a proton beam: a detailed study using INCL4.6-Abla07

Liquid lead-bismuth eutectic (LBE) is often considered as a possible target in spallation neutron sources. An experiment has been performed in 2005 at ISOLDE (CERN), in which LBE has been irradiated by 1.0 and 1.4 GeV protons and isotopes of astatine, a volatile precursor of Po, have been found. Until recently no model was able to reproduce this astatine production, which is due either to double charge exchange reactions, Bi(p,πxn)At, or to secondary reactions induced by helium nuclei. Recently, both parts of the spallation model combination INCL4-Abla have been improved leading to the new versions, INCL4.6-ABLA07. In particular, an additional mechanism to produce light and intermediate mass fragments has been added and special care has been paid to the low energy reactions. This paper first shows that all the basic features of the different reactions leading to astatine production are well predicted by the new model. The model, implemented into a beta version of MCNPX2.7 is then used to simulate the ISOLDE experiment. A very good agreement with the experimental data is observed.

Pion-nucleus elastic scattering, double-charge-exchange reactions, and subthreshold resonances

In the scattering of positive pions by nuclei the double-charge-exchange (DCX) reaction creates the possibility of the formation of pionic atom states in the vicinity of the threshold of the reaction. These quasistationary states can manifest themselves as resonances in the elastic scattering cross section. The strength and shape of these resonances are strongly affected by the instability of the nucleus created in the DCX channel. It is shown that this mechanism can explain oscillation structures in the excitation function observed in scattering of low-energy positive pions from ${}^{12}\mathrm{C}$.

A study of radiative double electron capture in bare chromium ions at the ESR

Radiative double electron capture is a fundamental atomic process which should be observed in collisions of bare ions with atoms, albeit with a much smaller cross-section than single radiative electron capture. A new experiment—to observe this rare process under single-collision conditions—has been performed at the internal gas jet target of the experimental storage ring at GSI in Darmstadt. X-ray spectra associated with single and double charge exchange have been observed in 30 MeV u−1 collisions of bare chromium ions (Cr24+) with helium and nitrogen target gases.

Unified Description of Pion Nuclear Reactions and Related Problems

Recent work on pion absorption, through the study of two- and three-body absorption, as well as a microscopic analysis of the Δ selfenergy in the medium has made possible the task of tackling from the theoretical point of view the study of all pion nuclear reactions around resonance in a unified way. We present here the results of such a unification for the inclusive pion nuclear reactions, quasielastic, single charge exchange, double charge exchange and absorption. At the same time, inspired by the mechanisms for pion absorption in the nuclear medium, we suggest new channels of annihilation for antiprotons in the nucleus and new decay modes for protons in the nucleus.

Modeling astatine production in liquid lead-bismuth spallation targets

Astatine isotopes can be produced in liquid lead-bismuth eutectic targets through proton-induced double charge exchange reactions on bismuth or in secondary helium-induced interactions. Models implemented into the most common high-energy transport codes generally have difficulties to correctly estimate their production yields as was shown recently by the ISOLDE Collaboration, which measured release rates from a lead-bismuth target irradiated by 1.4 and 1 GeV protons. In this paper, we first study the capability of the new version of the Liège intranuclear cascade model, INCL4.6, coupled to the deexcitation code ABLA07 to predict the different elementary reactions involved in the production of such isotopes through a detailed comparison of the model with the available experimental data from the literature. Although a few remaining deficiencies are identified, very satisfactory results are found, thanks in particular to improvements brought recently on the treatment of low-energy helium-induced reactions. The implementation of the models into MCNPX allows identifying the respective contributions of the different possible reaction channels in the ISOLDE case. Finally, the full simulation of the ISOLDE experiment is performed, taking into account the likely rather long diffusion time from the target, and compared with the measured diffusion rates for the different astatine isotopes, at the two studied energies, 1.4 and 1 GeV. The shape of the isotopic distribution is perfectly reproduced as well as the absolute release rates, assuming in the calculation a diffusion time between 5 and 10hours. This work finally shows that our model, thanks to the attention paid to the emission of high-energy clusters and to low-energy cluster induced reactions, can be safely used within MCNPX to predict isotopes with a charge larger than that of the target by two units in spallation targets, and, probably, more generally to isotopes created in secondary reactions induced by composite particles.

Spectroscopic Measurement in 9He and 12Be

Spectroscopy for neutron-rich nuclei 9He and 12Be has been performed by means of heavy-ion double charge exchange (HIDCX) (18O, 18Ne) reaction on stable target nuclei 9Be and 12C, respectively. Several clear peaks in 12Be at low excitation energy region even above neutron separation energy have been observed in one-shot measurement, whereas no prominent signals of 9He have been observed owing to the small cross section. It is shown that the HIDCX reaction is a new powerful spectroscopic tool for study of unstable neutron-rich nuclei.

26aGK-8 80MeV/Aにおける(^ B,^ Li)反応による二重電荷交換反応の測定(26aGK 宇宙核物理・軽イオン,実験核物理領域)

26aGK-8 80MeV/Aにおける(^ B,^ Li)反応による二重電荷交換反応の測定(26aGK 宇宙核物理・軽イオン,実験核物理領域)

Measurement and calculation of absolute single- and multiple-charge-exchange cross sections for Feq+ions impacting CO and CO2

Absolute cross sections are reported for single, double, and triple charge exchange of Fe${}^{q}$${}^{+}$ ($q=5--13$) ions with CO and CO${}_{2}$. The highly charged Fe ions are generated in an electron cyclotron resonance ion source. Absolute data are derived from knowledge of the target gas pressure, target path length, and incident and charge-exchanged ion currents. Experimental results are compared with new calculations of these cross sections in the $n$-electron classical trajectory Monte Carlo approximation in which the ensuing radiative and nonradiative cascades are approximated with scaled hydrogenic transition probabilities and scaled Auger rates. The present data are needed in astrophysical applications of solar- and stellar-wind charge exchange with comets, planetary atmospheres, and circumstellar clouds.

Production of doubly strange hypernuclei via [formula omitted] doorways in the [formula omitted] reaction at 1.8 GeV/c

We examine theoretically production of doubly strange hypernuclei, CΞ−16 and 16ΛΛC, in double-charge exchange O16(K−,K+) reactions using a distorted-wave impulse approximation. The inclusive K+ spectrum at the incident momentum pK−=1.8 GeV/c and scattering angle θlab=0° is estimated in a one-step mechanism, K−p→K+Ξ− via Ξ− doorways caused by a Ξ−p–ΛΛ coupling. The calculated spectrum in the Ξ− bound region indicates that the integrated cross sections are on the order of 7–12 nb/sr for significant 1− excited states with C14(0+,2+)⊗sΛpΛ configurations in 16ΛΛC via the doorway states of the spin-stretched N15(1/2−,3/2−)⊗sΞ− in CΞ−16 due to a high momentum transfer qΞ−≃400 MeV/c. The Ξ− admixture probabilities of these states are on the order of 5–9%. However, populations of the 0+ ground state with C14(0+)⊗sΛ2 and the 2+ excited state with C14(2+)⊗sΛ2 are very small. The sensitivity of the spectrum on the ΞN–ΛΛ coupling strength enables us to extract the nature of ΞN–ΛΛ dynamics in nuclei, and the nuclear (K−,K+) reaction can extend our knowledge of the S=−2 world.

Neutron-rich Hypernuclei

Production and spectroscopy of neutron-rich Λ hypernuclei by double-charge exchange reactions ( π − , K + ) on nuclear targets are investigated in a theoretical viewpoint. The Λ–Σ coupling in nuclei induces a Σ admixture, which is enhanced in a neutron-excess environment, and plays an important role in production by a one-step mechanism π − p → K + Σ − via Σ − doorways in these reactions. A feasibility of extracting the Σ − admixture probability in the neutron-rich 10 Λ Li hypernucleus by the 10B( π − , K + ) reaction is examined within a distorted-wave impulse approximation.

Review of theories on double electron capture in fast ion-atom collisions

This work reviews quantum-mechanical four-body distorted wave theories for double electron capture in collisions between fast heavy multiply charged ions and heliumlike atomic systems. The widely used distorted wave methods of the first- and second-order in the pertinent perturbation series expansions are compared with each other. This tests the presumed importance of double continuum intermediate states of two electrons. Further, the relative performance is evaluated of the second-order theories with and without the eikonalization of the two-electron Coulomb wave functions for double continuum intermediate states. This checks the correctness and usefulness of the eikonalized Coulomb waves when two electrons participate actively to the transition from the initial to the final state of the entire system. We also analyze the significance of the contributions from excited heliumlike states especially in comparison between theory and measurement. The overall goal of the present study is to determine how much of the unprecedented experience gained over several decades in studying high-energy theories of pure three-body charge exchange could be exported directly to four-body double-electron capture without much of additional and essential eleaborations, besides the naturally increased computational demand. In particular, we address the unexpected breakdown of the continuum distorted wave eikonal initial state approximation and the anticipated success of continuum distorted wave theory for double charge exchange in ion-atom collisions at high impact energies.

Feasibility of extracting aΣ−admixture probability in the neutron-richΛ10Lihypernucleus

We theoretically examine production of the neutron-rich ${}_{\ensuremath{\Lambda}}^{10}\mathrm{Li}$ hypernucleus by a double-charge exchange (${\ensuremath{\pi}}^{\ensuremath{-}}$, ${K}^{+}$) reaction on a $^{10}\mathrm{B}$ target with distorted-wave impulse approximation calculations. We calculate the inclusive spectrum at the incident momentum 1.20 GeV/$c$ by a one-step mechanism ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{\ensuremath{-}}$ via ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ doorways caused by a ${\ensuremath{\Sigma}}^{\ensuremath{-}}p\ensuremath{\leftrightarrow}\ensuremath{\Lambda}n$ coupling. The resultant spectrum can explain the magnitude of the recent experimental data, so that the ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ admixture probability in ${}_{\ensuremath{\Lambda}}^{10}\mathrm{Li}$ is found to be of the order of ${10}^{\ensuremath{-}1}%$. The (${\ensuremath{\pi}}^{\ensuremath{-}}$, ${K}^{+}$) reaction provides the ability to extract properties of wave functions with $\ensuremath{\Lambda}\text{\ensuremath{-}}\ensuremath{\Sigma}$ coupling effects in neutron-rich nuclei, as well as the reaction mechanism.

Resonant behaviour in double charge exchange reaction of [formula omitted]-mesons on the nuclear photoemulsion

The invariant-mass spectra of the pp π - and pp systems produced in the double charge exchange (DCX) of positively charged pions on photoemulsion are analysed. A pronounced peak is observed in the pp π - invariant-mass spectrum, while the M pp spectrum exhibits a strong Migdal–Watson effect of the proton-proton final-state interaction. These findings are in favor of the NN-decoupled NN π pseudoscalar resonance with T = 0 called d ′ .