Double Charge Exchange Research Articles

Study of baryon and search for dibaryon resonances by the $pp \rightarrow pp\pi^ + \pi^-$ reaction

Exclusive measurements of the two-pion production channel $pp \rightarrow pp\pi^ + \pi^-$ have been carried out near threshold at CELSIUS with the PROMICE/WASA detector. They reveal $pp \rightarrow pp^*(1440)\rightarrow pp\sigma \rightarrow pp(\pi^ + \pi^-)_{I = \ell = 0}$ as the dominant process at these energies, however, the data exhibit also significant contributions from $p^*(1440) \rightarrow \Delta \pi \rightarrow p(\pi^ + \pi^-)_{I = \ell = 0}$ . From the observed interference of these Roper decay routes their relative branching ratio is derived. The status on the search for NN-decoupled $NN\pi$ -resonances is reviewed with regard to recent experimental searches in the pionic double charge exchange in nuclei, the two-pion production in nucleon-nucleon collisions, the photo pion-production on the deuteron and the electro pion-production in nuclei.

Double charge exchange from helium neutral beams in a tokamak plasma

Helium neutral beams of 29.5 keV amu−1 have been injected into helium plasmas on the JET tokamak. Thermal neutral helium in its ground state forms along the beam trajectory due to resonant double charge exchange. The helium neutrals form a halo about the neutral beam axis, and the latter is observed spectroscopically. The cross section for double charge exchange is derived relative to the cross section for beam emission. The double charge exchange spectrum is used to measure the plasma ion temperature and the frequency of toroidal rotation and can be used to infer the helium ion density. The potential for a He ash diagnostic based on observation of the helium halo is discussed.

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.

Double-electron capture in relativistic U92+ collisions at the ESR gas-jet target

Total cross-sections for radiative single- and double-electron capture are measured in collisions of fast highly charged ions with light target atoms. Cross-sections for non-correlated double capture are in accordance with theoretical predictions. No significant line structure at twice the single K-radiative electron capture (K-REC) photon energy was observed. Angular distributions single K-REC photons associated with single- and double-charge exchange exhibit the same pattern.The corresponding REC lines are almost by a factor of two broader for double-charge exchange than in the single capture case.

Semiexclusive pionic double charge exchange on4He

The semiexclusive reaction ${}^{4}\mathrm{He}({\ensuremath{\pi}}^{+},{\ensuremath{\pi}}^{\ensuremath{-}}pp)pp$ has been studied at pion kinetic energies of 105 MeV and 115 MeV. Signatures from the production of the hypothetical $\ensuremath{\pi}\mathrm{NN}$ resonance ${d}^{\ensuremath{'}}$ have been searched for in the invariant mass ${M}_{\ensuremath{\pi}\mathrm{pp}}$ spectra. No hint for a dominant ${d}^{\ensuremath{'}}$ production, as anticipated from double charge exchange excitation functions on nuclei, has been found. The data are satisfactorily described by sequential single charge exchange.

Effects of Nuclear Structure in Double Charge Exchange Reactions on 16 O and 40 Ca

The energy dependence of forward double charge exchange (DCX) reaction is studied for the doubly closed shell nuclei 16O and 40Ca. A common characteristic of the two DCX reactions is a resonance-like peak around 50 MeV pion lab energy. While some authors have interpreted this peak as the evidence of a dibaryon resonance state, we show that it arises naturally in a two-step process in the conventional pion—nucleon system with proper handling of nuclear structure. The effects of nuclear structure are demonstrated through a comparison among different nuclear structure models: the symmetry model SU(4) ⊗ SU(3), the single particle shell model and the «realistic” shell model.

Pion double charge exchange on4He

The doubly differential cross sections for the $^4$He$(\pi^+,\pi^-) 4p$ reaction were calculated using both a two-nucleon sequential single charge exchange model and an intranuclear cascade code. Final state interactions between the two final protons which were the initial neutrons were included in both methods. At incident pion energies of 240 and 270 MeV the low-energy peak observed experimentally in the energy spectrum of the final pions can be understood only if the contribution of pion production is included. The calculated cross sections are compared with data.

The exotic double-charge exchange μ−→e + conversion in nuclei

The formalism for the neutrinoless ( μ −,e +) conversion is investigated in detail and the relevant nuclear matrix elements for light intermediate neutrinos in the case of 27Al( μ −,e +) 27Na are calculated. The nucleus 27Al is going to be used as a stopping target in the MECO experiment at Brookhaven, one of the most sensitive probes expected to reach a sensitivity in the branching ratio of the order 10 −16 within the next few years. The relevant transition operators are constructed utilizing a variety of mechanisms present in current gauge theories, with emphasis on the intermediate neutrinos, both light and heavy, and heavy SUSY particles. The nuclear wave functions, both for the initial state and all excited final states are obtained in the framework of 1s–0d shell model employing the well-known and tested Wildenthal realistic interaction. In the case of the light intermediate neutrinos the transition rates to all excited final states up to 25 MeV in energy are calculated. We find that the imaginary part of the amplitude is dominant. The total rate is calculated by summing over all these partial transition strengths. We also find that the rate due to the real part of the amplitude is much smaller than the corresponding quantity found previously by the closure approximation.

Helium doped hydrogen or deuterium beam as cost effective and simple tool for plasma spectroscopy

Energetic neutral particles from neutral hydrogenic beam heating systems are widely used for active spectroscopic measurements of key plasma parameters in fusion experiments. Helium beams are used in dedicated diagnostic beamlines offering deeper penetration and resonant double charge exchange with alpha particles. Neutral beam systems using pure helium either require specialised helium gas pumping with a pumping speed in excess of 1000 m 3/h or are restricted to short pulses (normally less than 1 s). A doped hydrogen/helium beam combines the requirements for plasma heating and diagnostics without the need for sophisticated helium pumping. A small flow of helium gas is injected into the plasma source for the time helium particles are required. The helium current is typically 10% of the total extracted current. The reduction in heating power of the doped beam can be kept below 5%. Doped deuterium/helium beams have been successfully tested and routinely used at JET. HeI beam emission spectra obtained with a doped deuterium/helium beam offer sufficiently strong visible lines for spectroscopic applications.

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.

Double Electron Capture in Relativistic U92+ Collisions Observed at the ESR Gas-Jet Target

Processes associated with double electron capture into bare U92+-ions have been observed under single collision conditions. Regions of very low cross sections, close to mbarn, have been explored successfully. In particular, an attempt to register photons with twice the energy of single K-REC photons has been performed. Moreover, K-REC spectra associated with double charge exchange have been analysed in terms of their angular distribution. As a result, evidence for correlated electron capture has been found

Systematics of the low-energy pionic double charge exchange in nuclei

The experimental results for the $({\ensuremath{\pi}}^{+},{\ensuremath{\pi}}^{\ensuremath{-}})$ reaction on nuclei obtained in recent years reveal clear systematic features of this reaction. New data on ${}^{7}\mathrm{Li},$ ${}^{12}\mathrm{C},$ ${}^{16}\mathrm{O},$ and ${}^{56}\mathrm{Fe}$ supplementing the existing data base are presented. The data on ${}^{12}\mathrm{C}$ are partly at variance with previous results. The dependence of the cross sections on incident energy, scattering angle, and on the target mass is discussed for transitions leading to the ground state of the final nucleus or to the double isobaric analog state.

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.

Measurement of Charge Exchange and X-Ray Emission Cross Sections for Solar Wind-Comet Interactions.

X-ray emission from a comet was observed for the first time in 1996. One of the mechanisms believed to be contributing to this surprisingly strong emission is the interaction of highly charged solar wind ions with cometary gases. Reported herein are total absolute charge-exchange and normalized line-emission (X-ray) cross sections for collisions of high-charge state (+3 to +10) C, N, O, and Ne ions with the cometary species H2O and CO2. It is found that in several cases the double charge-exchange cross sections can be large, and in the case of C3+ they are equal to those for single charge exchange. Present results are compared to cross section values used in recent comet models. The importance of applying accurate cross sections, including double charge exchange, to obtain absolute line-emission intensities is emphasized.

Two-nucleon one-loop corrections to pion double charge exchange within heavy baryon chiral perturbation theory

One-loop corrections at the two-nucleon level to pion double charge exchange scattering off a nuclear target at threshold are calculated within the framework of heavy baryon chiral perturbation theory. An estimate for the (two-nucleon) one-loop correction is obtained in the static limit and using an impulse approximation. We find a small (1.6%) increase relative to the leading order tree graphs.

Helium doped hydrogen or deuterium beam as cost effective and simple tool for plasma spectroscopy

Energetic neutral particles from neutral beam heating systems are widely used for active spectroscopic measurements of key plasma parameters in fusion experiments. Both the plasma discharges and the neutral beam systems are normally operated with hydrogen or deuterium. Helium beams are used in dedicated diagnostic beam lines as they offer deeper penetration and are subject to less background radiation and enable resonant double charge exchange with alpha particles. Neutral beam systems using pure helium either require specialized helium gas pumping with a pumping speed in excess of 1000 m3/h or are restricted to short pulses (normally less than 1 s). A doped hydrogen/helium beam combines the requirements for plasma heating and diagnostics without the need for sophisticated helium pumping. A small flow of helium gas is injected into the plasma source for the time helium particles are required. The helium current is typically 10% of the total extracted current. The reduction in heating power of the doped beam can be kept below 5%. The small amount of helium gas does not cause an excessive pressure rise along the beam line and does not reduce the reliability of the beam heating system. Doped deuterium/helium beams have been successfully tested and routinely used at JET. The Hel beam emission spectra obtained with a doped deuterium/helium beam produce sufficiently strong visible lines for spectroscopic applications. Furthermore, the simultaneous availability of helium and hydrogenic particles in the beam allows us to extend spectroscopic measurements to another atomic system and hence cross-check results from helium beams with those from hydrogenic beams. The only investment required is an additional helium gas inlet system into the ion source.

Inclusive measurements of pionic double charge exchange on 3He at low energies

Using the CHAOS spectrometer at TRIUMF pion momentum spectra and angular distributions were measured for the 3He( π −, π +) reaction at incident energies from 65 to 120 MeV and total cross sections were deduced. The data are compared to Monte Carlo simulations for the conventional reaction process as well as to predictions for the production of the hypothetical πNN resonance d′ with and without collision damping.

πNNdecay of a possibled′dibaryon in the3P0quark pair creation model

We study the pionic decay of a possible dibaryon ${d}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\pi}+NN$ and pion decay of single baryons. The ${}^{3}{P}_{0}$ quark-pair-creation model is used for the definition of the effective quark-pion coupling. All necessary coupling constants and vertex form factors both in the baryonic and dibaryonic sectors are calculated in this model using translationally invariant quark-shell-model configurations. A hypothesis for the mass shift of the ${d}^{\ensuremath{'}}$ in a nuclear medium is discussed in order to explain the position of the resonance peak observed in double-charge exchange reactions in nuclei and the nonobservation (or at least doubtful observations) of the ${d}^{\ensuremath{'}}$ as a free resonance outside of a nuclear medium. In this connection the dependence of the ${d}^{\ensuremath{'}}$ decay width on the ${d}^{\ensuremath{'}}$ mass is calculated for two alternative models of the final-state $\mathrm{NN}$ interaction (one-boson exchange potential and Moscow potential). Off-shell effects in the ${d}^{\ensuremath{'}}$ decay are studied on the basis of an algebraic quark-cluster model technique.

D′ production in heavy-ion collisions

The production of d′ dibaryons in heavy-ion collisions due to the elementary process NN → d′π is considered. The NN → d′π cross section is estimated using the vacuum d′ width Γ d′ ≈ 0.5 MeV extracted from data on the double charge exchange reactions on nuclei. The d′ production rate per single collision of heavy ions is estimated at an incident beam energy of 1 A GeV within the framework of the Quantum Molecular Dynamics transport model. We suggest to analyse the invariant mass spectrum of the NNπ system in order to search for an abundance of events with the invariant mass of the d′ dibaryon. The d′ peak is found to exceed the statistical fluctuations of the background at a 6σ level for 2 × 10 5 · A central collisions of heavy ions with the atomic number A.