Double Charge Exchange Cross Sections Research Articles

State-selective Charge Exchange in 19.5–100 keV amu−1 O6+ Collision with He and H2

The cross sections of state-selective charge exchange (CX) between highly charged ions and neutrals are important for modeling extreme ultraviolet and soft X-ray emissions in many astrophysical objects with hot plasma impacting cold media. By using cold-target recoil-ion momentum spectroscopy, we measure O6+ CX collisions with He and H2 in the collision energy range of 19.5 to 100 keV amu−1. The relative cross sections of state-selective single CX are reported for electron capture into O5+(1s 2 nl) n = 2, 3, 4, 5, ≥6 and n = 3, 4, 5, ≥6 for He and H2, respectively. With the collision energy increasing to 100 keV amu−1, the main capture channel shifts to higher n for both target species as compared to available theoretical results. We also report state-selective cross sections for double CX with He, where doubly excited states of with being 2s 2 (1S), 2s2p (1P), 2p 2 (1D), and 2p 2 (1S) [symmetric configurations] and 2s3l, 2p3l−2s4l, and 2s5l−2p5l [asymmetric configurations] are distinguished. It is found that the contributions of doubly excited states with asymmetric configurations are dominant and symmetric configurations increasingly come into play with the increase of collision energy. The present results provide experimental benchmarks available for theoretical calculations.

Benchmark n ℓ-resolved Cross Sections of Single and Double Charge Exchange Processes in 1.67–20 keV u−1 C4+ Collisions with He

State-resolved charge exchange (CX) cross sections are of the utmost importance for modeling related photon emissions existing in a broad range of astrophysical environments. With the cold-target recoil-ion momentum spectroscopy, we determined with high accuracy the state-resolved single and double CX cross sections at the quantum orbital angular momentum level for solar wind ion C4+ collisions with He in an energy range of 1.67–20 keV u−1, which allow one to benchmark the CX calculations in great detail, and to test the applicability of the analytical n- and ℓ-distribution models widely adopted by the astrophysical community. We found that the present measurements are well reproduced by the most recent state-of-the-art atomic–orbital close-coupling calculations. However, the CX models failed to give a consistent description on the measured ℓ distributions. The present work reveals that the velocity and collision partner species dependence effects as well as electronic correlations for multielectron processes should be included in an improved model. Alternatively, in future modeling to interpret high-resolution astrophysical observations the more elaborate quantum-mechanical calculations may be resorted to with confidence.

The NUMEN Project: Toward New Experiments with High-Intensity Beams

The search for neutrinoless double-beta (0νββ) decay is currently a key topic in physics, due to its possible wide implications for nuclear physics, particle physics, and cosmology. The NUMEN project aims to provide experimental information on the nuclear matrix elements (NMEs) that are involved in the expression of 0νββ decay half-life by measuring the cross section of nuclear double-charge exchange (DCE) reactions. NUMEN has already demonstrated the feasibility of measuring these tiny cross sections for some nuclei of interest for the 0νββ using the superconducting cyclotron (CS) and the MAGNEX spectrometer at the Laboratori Nazionali del Sud (LNS.) Catania, Italy. However, since the DCE cross sections are very small and need to be measured with high sensitivity, the systematic exploration of all nuclei of interest requires major upgrade of the facility. R&D for technological tools has been completed. The realization of new radiation-tolerant detectors capable of sustaining high rates while preserving the requested resolution and sensitivity is underway, as well as the upgrade of the CS to deliver beams of higher intensity. Strategies to carry out DCE cross-section measurements with high-intensity beams were developed in order to achieve the challenging sensitivity requested to provide experimental constraints to 0νββ NMEs.

Measurement of Absolute Single and Double Charge Exchange Cross Sections for Si(7–10)+ at 0.88–2.50 KeV/u Impacting He and H2

Abstract First measurements are reported for total, absolute, single, and double charge-exchange (CE) cross sections for Si(7–10)+ ions in the solar wind (SW), colliding with the prevalent astrophysical species H2 and He found in comets, the interplanetary medium, and planetary atmospheres. Measurements are in the energy range 0.88–2.50 keV/u, corresponding to the energies of the “fast” and “slow” ion components of the SW. Limited agreement is found with single-exchange results calculated in the classical over-the-barrier model. These CE data are useful for understanding, in laboratory and astrophysical plasmas, photon emissions in the X-ray to visible energy range arising from resulting ion-stabilization steps.

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.

Absolute cross sections for single and double charge-exchange in Feq+impacting on He

We report measured absolute single and double charge-exchange cross sections (CSs) for Feq+ions with He at the ion impact energy of 7.0 × q keV forq = 5–13.The range of ion velocities is 350 km s−1 forq = 5, to 560 km s−1for q = 13,comparable to typical solar wind velocities. A retarding-field method is used forcharge-state analysis of the ion beam after traversing the stationary target gascell. The CSs are determined from absolute measurements of the ion currents andHe target gas pressure.

Inclusive pion double charge exchange on 16O at 0.6–1.1 GeV

The inclusive pion double charge exchange (DCX) on oxygen nuclei has been measured in the region where additional pion production is kinematically forbidden. The experiment was performed at the ITEP PS at incident π − kinetic energies T 0=0.59, 0.75 and 1.1 GeV. The integrated forward differential cross section was found to decrease with energy slowly. At 1.1 GeV it exceeds the theoretical prediction within the conventional sequential single charge exchange mechanism with a neutral pion in the intermediate state (Glauber elastic rescattering) by about a factor of five. The sequential mechanism with two pions in the intermediate state (Glauber inelastic rescatterings), which was proposed recently, seems to be able to explain the observed energy dependence and allows to predict the DCX cross section at higher energies.

Implications of inelastic rescatterings for pion doublecharge exchange on nuclei

Different aspects of the Gribov-Glauber approach for the calculation ofinclusive pion double charge exchange (DCX) cross sections on nuclei areinvestigated. Recently, we have shown that inelastic rescatterings (IRs)with two (and more) pions in the intermediate states give an importantcontribution to the process of DCX at energies above ~ 0.6 GeV. Inthis paper we use the one-pion exchange model to study in detail theamplitude of two-pion production. This allows us to verify theoreticalassumptions made in the previous paper and to predict the forwardinclusive pion DCX cross section at energies ≳1 GeV, where IRsdominate over the conventional DCX mechanism of two sequentialsingle-charge exchanges.

Pion elastic scattering and double charge exchange on heavy nuclei in the generalized seniority model

The $\ensuremath{\pi}$-nucleus optical potential is extended to open shell nuclei by employing the generalized seniority model and partial Pauli blocking. The calculated optical potentials are fit to $\ensuremath{\pi}$-nucleus elastic scattering data on ${}^{90}\mathrm{Zr}$ and ${}^{208}\mathrm{Pb}$ at resonance as well as low energies. The ranges of the $\ensuremath{\pi}N$ interaction are determined by a best fit to experimental data. The angular distribution at 48 MeV pion lab energy and energy dependence of the double charge exchange cross section on Te isotopes are calculated. The existing experimental data are reproduced by using the ranges in the vicinity of the averaged ranges of ${}^{90}\mathrm{Zr}$ and ${}^{208}\mathrm{Pb}$ determined in fitting elastic-scattering data.

Energy dependence of cross sections for pion double charge exchange on60,62,64Ni

Double charge exchange cross sections have been measured at ${\ensuremath{\theta}}_{L}=5\ifmmode^\circ\else\textdegree\fi{}$ and ${T}_{\ensuremath{\pi}}=$ 230, 180, and 140 MeV for targets of ${}^{60,62,64}$Ni. Results are compared with previous data at 292 MeV and with a generalized seniority model.

Active Electrons in the CHe 4+ Quasimolecule

Low energy C4++ He collisions are known to be unusual in the sense that double-electron transfer dominates single capture. A basic question is whether one, two or more active electrons play a role in these processes. To study this problem, results are reported for the molecular energies and dynamical couplings of the CHe4+ system, modified with a common translation factor. The interactions that are responsible for the capture processes are discussed in detail, and as recently proposed in the literature, double capture is shown to occur simultaneously through essentially single-electron interactions. Some illustrative results of single- and double-charge exchange cross sections are also presented.

Isospin dependence of double analog cross sections at T pi =400-500 MeV.

At energies in the range 400\char21{}500 MeV, pion-induced double charge exchange cross sections leading to the double analog state appear to behave differently for even and odd isospin.

Test of generalized seniority with pion double charge exchange on the nickel isotopes.

Recent experimental double charge exchange cross sections to the double analog state and the ground state are compared to predictions of the generalized seniority model.

Pion double charge exchange on 16O at T pi =300-500 MeV.

Measurements of small-angle cross sections for the pion double-charge-exchange (DCX) reaction $^{16}\mathrm{O}$(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${)}^{16}$Ne (g.s.) at incident energies of 300\char21{}500 MeV are reported. These are the first measurements of DCX cross sections on a T=0 nucleus in this energy region. The behavior of the cross sections is similar to that of analog transitions, but they are smaller by more than an order of magnitude. This suggests sequential charge-exchange scattering as the dominant process, but suppressed by a mechanism not yet identified.

Systematics of the double isobaric analog state cross section at 50 MeV.

Double charge exchange cross sections for 50 MeV pions to double isobaric analog states in $^{44}\mathrm{Ca}$, $^{56}\mathrm{Fe}$, and $^{93}\mathrm{Nb}$ were measured. The results indicate that the effective double charge exchange operator at this energy has a strong short-range component. In addition, evidence is presented tending to implicate isospin mixing as the mechanism for excitation of the analog of the antianalog in $^{93}\mathrm{Nb}$.

Measurement of pion induced double charge exchange on 34S and 56Fe at Tπ = 50 MeV

Measurements of double charge exchange cross sections at an incident π + energy of 50 MeV in the angular range 10°–90° are reported for analog and non-analog transitions on 34S and 56Fe. In the case of 56Fe several individual non-analog transitions have been observed and their angular distributions measured. A state 1.5 MeV below the double isobaric analog state in 56Ni, which recently has been observed at high incident pion energies as well, shows a peculiar backward peaked angular distribution.

Dynamical correlations in low-energy pion double charge exchange

We consider various processes that contribute to low-energy pion double charge exchange (DCX), and we study their sensitivity to short-range correlations. Within the framework of the fixed-nucleon field theory, we derive a general expression for the following two-nucleon DCX processes: two sequential single charge exchanges via intermediate π (SEQ-π) plus ϱ (SEQ-ϱ) exchange and the lowest-order Δ 33-nucleon (Δ-N) interactions via explicit π + ϱ exchange. We retain the full spin dependence of the various contributions, and we present the results in a form that can be used for any transition whose corresponding two-body density matrix elements are known. Detailed evaluations are made for 14C to illustrate the importance of short-range correlations. We show the effects on the calculated DCX cross sections that result from three different wave functions: two defined entirely within the p-shell and the other involving configuration mixing with the sd-shell. Our results indicate that SEQ-π is the dominant mechanism for low-energies and that the inclusion of the short-range correlation function decreases the cross section by nearly 50% for standard choices of the pion-nucleon interaction. The largest contribution to the cross section from configuration mixing occurs in off-diagonal transitions [e.g., (0 p) 2 to (0 d) 2]. Pairs of nucleons coupled to spin S = 0.are substantially more sensitive to the short-range correlations than pairs coupled to S = 1. The size of the ϱ-meson contribution to the SEQ mechanism is somewhat model-dependent, but the size of the Δ-N interaction is fixed from other sources. The SEQ-ϱ contribution and the Δ-N interaction are about 5–20% effects, and they may increase or decrease the cross section, depending upon details such as the energy or the amount of configuration mixing.

Dynamical short-range correlations in low-energy pion double charge exchange on the calcium isotopes

We consider the influence of correlations on pion double charge exchange (DCX) from the Ca isotopes at low energy. Our study includes shell-model correlations and various short-range correlations, including repulsive correlations and ϱ-meson exchange between nucleon-nucleon (NN) and delta-nucleon (ΔN) pairs. Although the relative DCX cross sections vary by as much as a factor of two with and without dynamical short-range correlations, experiment cannot yet distinguish between the models.

Short-range contribution to the pion-nucleus double-charge-exchange reaction due to quark-antiquark annihilation

We propose a new approach, namely a quark-antiquark annihilation mechanism, for the calculation of the short-range contribution to the pion double-charge-exchange (DCX) reaction. The angular distributions for the 26Mg(π +, π −) 26Si reaction at 50 MeV and reactions for the 18O at energies ranging from 24 to 79 MeV are calculated and compared with the data. The sensitivities of the calculation parameters in the model are discussed. We find that this process makes a large contribution to DCX and can account for most of the DIAS DCX cross sections in the forward-angle region at low energies.

Two-amplitude model for the energy dependence of double charge exchange on 18O.

A naive two-amplitude model, in which one amplitude is independent of energy and the other is , gives an excellent fit to the energy dependence of the double charge exchange cross section on $^{18}\mathrm{O}$.