S. H. Rokni

Isobaric-analog-state transitions in pion charge-exchange reactions above the Δ(1232) resonance

Forward-angle differential cross sections for the (π+, π0) reaction to isobaric analog states were measured at 300, 425, 500, and 550 MeV on targets ranging in mass from 7Li to 208Pb. The extrapolated 0° cross sections are found to rise markedly between 300 and 425 MeV, contrary to the behavior of the free πN process. The mass and energy dependence of the cross sections at the higher energies are discussed within the framework of the Glauber model.

Measurements of quasi-elastic pion single charge exchange on 3He at Tπ = 245 MeV

Abstract Differential cross sections from 3He(π±, π0) and 3He(π±, π0p) measurements are presented. The π0 energy spectra from 3He(π±, π0) and 3He(π+, π0p) are characteristic of quasi-free reactions. The proton angular distribution from 3He(π+, π0p) also show evidence of a quasi-free mechanism. Indications of multi-nucleon processes are presented in the 3He(π−, π0p) data. At least two nucleons must be involved. Comparisons between coincidence and single-arm measurements from this work and previous measurements of charged pion scattering on 3He provide evidence of an enhanced multiple scattering contribution to the charge exchange channel.

Nonanalog 0+(g.s.)→0+(g.s.) transitions in pion double charge exchange reactions on 128Te and 130Te

Abstract Small-angle (π + , π − cross sections for the 0 + (g.s.)→0 + (g.s.) transition in ββ-decay-allowed nuclei 128 Te and 130 Te were measured in the Δ 33 resonance region. The ratio of the cross section for 130 Te to that for 128 Te is 2.92±1.38 , in opposite trend to the currently accepted A −4 3 dependence of the nonanalog (π + , π − ) transitions. Possible consequences on the interpretation of geochemical ββ-decay half-life ratio are discussed.