A dependence of inclusive pion double charge exchange

The A dependence of the forward cross section for inclusive pion double charge exchange on nine target nuclei from ⁶Li to ²⁰⁹Bi at T₀ = 0.59 GeV, as well as the cross section for ⁶Li, ⁷Li, and ¹²C nuclei at T₀ = 0.59, 0.75, and 1.1 GeV, was measured with the 3-m magnetic spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The resulting A dependence is well described within the model involving two sequential single charge exchanges and taking into account the renormalization of the amplitude for pion single charge exchange in a nucleus. A relatively weak energy dependence of the cross section for the ⁶Li, ⁷Li, and ¹²C nuclei agrees with the analogous dependence obtained previously for the ¹⁶O nucleus, but it contradicts the predicted sharp decrease in the cross section within the model involving two sequential single charge exchanges. This result provides an additional piece of evidence that the contribution from the mechanism of inelastic Glauber rescattering is significant at T₀ ? 0.6 GeV.     

Contribution of the σ meson exchange to pionic double charge exchange reaction

The contribution of the σ meson exchange to the pionic double charge exchange (DCX) reaction is investigated. A concrete calculation on the forward excitation function of the low energy DCX reaction ¹⁴C(π⁺, π⁻)¹⁴O has been performed. It shows that the contribution of the σ meson exchange can reproduce well the resonance like excitation function of low energy DCX reaction. Received: 5 August 1998     

Inhomogeneous ferromagnetism and unconventional charge dynamics in disordered double exchange magnets

We solve the double exchange model in the presence of arbitrary substitutional disorder by using a self-consistently generated effective Hamiltonian for the spin degrees of freedom. The magnetic properties are studied through classical Monte Carlo while the effective exchange, D(ij), is calculated by solving the disordered fermion problem, and renormalized self-consistently with increasing temperature. We present results on the conductivity, magnetoresistance, optical response, and "real space" structure of the inhomogeneous ferromagnetic state, and compare our results with charge dynamics in disordered La1-xSrxMnO3. The large sizes, O(10(3)), accessible within our method allows a complete, controlled calculation on the disordered strongly interacting problem.     

Energy dependence of the charge exchange reaction from muonic hydrogen to oxygen

The charge exchange reaction of negative muons from the atom to oxygen has been measured in gaseous mixtures of H₂ + O₂. The measurements were performed at three different relative oxygen concentrations ranging from 0.2% to 0.8% and total pressures 3.5–15 bar. A mean transfer rate of , describing the transfer from the ground state of thermalized atoms to oxygen, was determined. In order to investigate the energy dependence of the transfer rate, Monte Carlo simulations of the thermalization and the muon transfer were carried out. The comparison of measured and simulated time spectra yielded an epithermal transfer rate =3.9 10¹¹ s^-1 in the energy interval 0.12–0.22 eV. The analysis with the model of Two components shows that all measured time spectra can be reproduced with the same set of parameters.     

Amplitude analysis of πN charge exchange at large momentum transfer

We have found evidence for the right-signature zero at t ≈ ?1.5 (GeV/c)² and the second wrong-signature zero at t ≈ ?2.5 (GeV/c)² in the helicity flip ?-Regge-pole exchange from an amplitude analysis of πN charge exchange extended to large momentum transfer. Reconstruction of the imaginary part of the nonflip amplitude suggests a remarkable degree of Regge behaviour out to large ?t. Confirmation of such behaviour would undermine the basic features of absorptive cut models.