Charge Exchange Channels Research Articles

Dispersion theory of parity non-conservation in pion-nucleon scattering at low energies

We examine the possibility for testing the weak parity non-conserving (pnc) interaction in pion-nucleon scattering at low energies. We start out analysis by assuming the existence of a pnc πNN coupling which conserves time reversal invariance and has the isospin selection rule ΔI = 1, and the existence of fixed- t dispersion relations obeyed by the pnc invariant amplitudes. By using the nonrelativistic expansion, we then derive dispersion relations for the partial-wave amplitudes. We calculate parity-odd observables in π −p → π −p and in π −p → π 0n, e.g., the up-down asymmetry α in the total cross section for a polarized target and the longitudinal polarization P of the recoil nucleon. In the conventional Cabibbo model for the weak interaction P and α are found to be of order 10 −7 to 10 −8. We have also examined the t-channel pnc ϱ-exchange process which has the isospin selection rule ΔI = 0, 2 and found it to contribute dominantly to P in the charge-exchange channel π −p → π 0n.

Direct vibrational excitation of ions and molecules via charge exchange in N+2–N2, O+2–O2, CO+–CO, and NO+–NO collisions

Differential and integral cross sections for direct vibrational excitation in symmetric N+2(X 2Σ+g, υ′0) –N2(X 1Σ+g, υ″0), O+2(X 2Πg, υ′0) –O2(X 3Σ−g, υ″0), CO(X 2Σ+, υ′0) –CO(X 1Σ+, υ″0) and NO+(X 1Σ+, υ′0) –NO(X 2Πr, υ″0) collisions have been determined for ions with 0.004 to 2.2 keV kinetic energies. Inelastic channels in the individual symmetric ion–molecule systems are strongly coupled to each other and to the energy resonant charge exchange channels. Differential cross sections for excitation of individual inelastic product channels have been computed as a function of scattering angle using a multistate impact parameter description of the collision. Small angle scattering dominates and becomes more concentrated in the forward direction with increasing ion kinetic energy. Multistate integral cross sections for individual channels and integral cross sections summed over all product channels are presented as a function of both ion kinetic energy and reactant ion vibrational state.

Formula omitted] production in K −p→NK3 π final states at 10 GeV/ c

Results are presented for reactions of the type K − p→ K ∗ (890) ( Nππ) at 10 GeV/ c where the K ∗ is produced forwards and the nucleon and two pions are all produced backwards in the c.m. Of the three real parts of the K ∗ density matrix elements only one is non-zero, while all imaginary parts are consistent with zero. In the non-charge-exchange channel, K − p→ K ∗−( Nππ) + , natural and unnatural spin-parity exchanges are equally important, while in the charge-exchange channels, K − p→ K ∗0( Nππ) 0 , unnatural spin-parity exchanges dominate. These results are compared to those for K − p→ K ∗ o ( Nπ) and found to be very similar for both the charge and non-charge-exchange reactions. However, they are different from those for K − p→ K ∗ o N .

Direct vibrational excitation via charge exchange in symmetric ion–molecule collisions

Integral and differential cross sections for vibrational excitation in symmetric H+2(X 2Σ+g, v′0) + H2(X 1Σ+g, v″0) collisions have been determined for incident kinetic energies E (keV) in the range 0.01<E<2.0. A multistate impact parameter description of the collision was used. At low kinetic energies, the inclusion of a relatively small number of states in the wavefunction expansion of the system achieves converged cross sections while at high energies a large number of product states are needed. The inelastic channels in this symmetric system are strongly coupled to each other and to the energy resonant charge exchange channels. Differential cross sections for excitation of individual product channels have been computed as a function of scattering angle within the multistate impact parameter approach. Small angle scattering within several degrees is dominant with forward inelastic scattering becoming more pronounced as the ion kinetic energy is increased. Integral cross sections for individual channels and integral cross sections summed over all product channels are presented as a function of both ion kinetic energy and reactant internal energy.

Pion condensation in neutron star matter: (II). Nuclear forces and stability

This paper presents several stable models of charged-pion condensed neutron star matter. The non-relativistic limit of the chirally symmetric Weinberg Lagrangian is used to describe interactions of the condensed pion field with the nucleons, as well as the pi-pi interactions of the condensed field. In the absence of nucleon-nucleon interactions, matter in this model is unstable, tending to ever-increasing baryon density and condensate wave vector. The connection of this model of condensation with the σ-model is shown. A general framework for including nuclear forces is then laid out. Results are given for a simple model in which the nuclear forces are assumed to produce an interaction energy V( ρ) dependent only on the total baryon density, independent of the degree of pion condensation, and also to produce a constant G-matrix element g in the nucleon-nucleon charge exchange channel. In the absence of condensation the equation of state reduces to that of interacting normal matter. We also consider effects of beta equilibrium and form factors in the p-wave pion-nucleon interaction. The condensed models are stable. Depending on the choice of parameters the models exhibit first- or second-order pion condensation phase transitions, or both.

Does Pickup to Analog States Exhibit a Charge Dependence of the Nuclear Force?

Discrepancies between observed ratios of $d$, $^{3}\mathrm{He}$ and $d$, $t$ yields populating analog states in $^{18}\mathrm{O}$ and $^{18}\mathrm{F}$ and ratios calculated by standard distorted-wave theory, which were thought to provide evidence for a charge-dependent nuclear interaction, are resolved by extending the conventional theory to include both an explicit charge-exchange channel in the continuum and fo\ifmmode \acute{r}\else \'{r}\fi{}m factors generated from a microscopic analysis.

Some energy curves of ArH+and their use in the study of the scattering of H+by Ar

Calculations on the ground state and some excited states of ArH+in the LCAO-STO-MO-SCF approximation are reported. The ground state interaction potential is then used to study the elastic scattering of protons by argon atoms at low and moderate energies. Partial wave calculations involving the JWKB evaluation of the phase shifts are compared to the available experimental results and subsequently used to improve the well depth obtained in the ab initio calculation. The values U=4.3 eV and Re=1.34 AA are thus found. Qualitative discussions of the approximate excited states lead to the conclusions that the excitation of the argon target, at moderate energies, can take place only via the charge exchange channel-that is, the four lowest monoexcited states of ArH+-at R1approximately=1 AA. This charge exchange channel being itself coupled to the ground state at internuclear distances 1.70 AA<or approximately=Rx<or approximately=1.85 AA. A tentative explanation of the preferential excitation Ar*(3p53d) is given.

Elastic and inelastic scattering of Li+ions by He

Elastic and inelastic differential measurements of the Li+-He system were undertaken with particular attention given to the charge exchange channels. The energy variation of the 'summed' differential cross sections (elastic, inelastic and change exchange) agrees quite well with the published ab initio ground state calculation, showing that most important channels are considered. All the inelastic and charge exchange processes are discussed in the frame of the diabatic correlation diagram.

Production of the g-meson in πN → g 0N charge exchange channels at 7 GeV/ c

Data from π +d and π −p experiments at 7 GeV/ c have been combined to yield 10 654 events in the π + π − mass spectrum. A spin-parity analysis of this data favors a spin-parity assignment of J P = 3 − for the g 0 (1670) meson. Spin-parities 1 − and 5 − were not in agreement with our data. An analysis of the differential cross section for ϱ 0, f 0 and g 0 production using the one-pion exchange model plus form factors was consistent with significant widths for g 0 decays to channel other than π + π −, while being in good agreement with the experimental branching ratios for ϱ 0 and f 0 mesons.

Regge analyses of ρ0 production in πN charge exchange channels at 7 GeV/ c

2380 events in the π + π − mass interval 0.68 < m( π + π −) < 0.88 GeV from π +d → pp π + π − and π −p → π + π −n experiments at 7 GeV/ c have permitted an analysis of ρ 0 production to be made for momentum transfer, | t| < 1.0 (GeV/ c) 2. Thedata were found to be in good agreement with a Regge π+A 2 model including absorption, but were not well described by a Regge π model plus absorption. The data and our Regge analyses were consistent with the absence of a nonsense wrong signature zero in the pion Regge amplitude for | t| < 1.0 (GeV/ c) 2. The π+A 2 Regge analysis of our ρ 0 data was compared with similar analyses used to describe π + photoproduction data, and was found to be in agreement with the predictions of vector dominance.

Charge Exchange and Production ofηMesons and Multiple Neutral Pions inπ−pReactions between 654 and 1247 MeV/c

An experiment designed to study the π−p total neutral cross section and its breakdown into several channels has been performed at eleven incident pion momenta ranging from 654 to 1247 MeV/c. Angular distributions for the charge exchange π0 and for η0 production are given in terms of Legendre-polynomial expansion coefficients. Forward and backward differential cross sections are presented for the charge-exchange channel and comparisons with recent dispersion-relation predictions for the forward cross section are made.Received 2 June 1969DOI:https://doi.org/10.1103/PhysRev.187.1827©1969 American Physical Society

Eine Methode zur Erzeugung von Strahlen negativer Ionen

A new method for the production of beams of negative ions to be injected into a tandem Van de Graaff accelerator is presented. Negative ions of a desired species are produced by impact of noble gas ions with molecules of a gas containing this element, and are then collected and bent into a beam with high efficiency. For example, a beam of negative fluorine ions has been obtained by bombardment of boron fluoride with 30 keV krypton ions, resulting in a current of 0·5 μA of F++++ at the target. The original ion source of the tandem has been used with this modified procedure. The krypton gas has been fed into the duoplasmatron and the boron fluoride into the charge exchange channel. No damage to the ion source system has been observed, even in this case. This method has also been applied to nitrogen and oxygen with good results. Some measurements are reported, and a brief discussion of the basic process of the method is given.