Axial vector meson production

Recently available differential cross section and density matrix information on π^?p → B^?p at 4 GeV/c are successfully described in terms of t channel exchanges and s channel absorptive effects. The s channel helicity amplitude which is dominant at small |t| (zero net helicity flip ω exchange) is found to have a zero at ?t = 0.2 GeV². SU(3) and higher symmetries are used to predict cross sections for further axial vector meson production processes, in particular non-diffractive A₁ production. The importance of these processes with regard to Regge phenomenology and meson spectroscopy is emphasized.     

Regge pole and cut behaviour at Fermilab energies

Prompted by some unusual features of the np charge-exchange cross sections recently measured at Fermilab, we study this process over the entire energy range in an attempt to clarify its exchange amplitude structure. Comparison with all the other two-body processes so far measured at Fermilab (π^?p → π⁰n, νn, ω⁰n and elastic scattering) allows one to draw useful conclusions concerning the required J-plane structure of Regge cut models. We show that the shrinkage properties and helicity dependence of Regge cuts must be more complicated than current models suggest. We also present evidence that the Williams (or “poor man's absorption”) model for π exchange is incorrect at high energies.     

Regge description of nucleon-nucleon polarisation

Recent polarisation data for pp and pn elastic scattering within the momentum range 6 to 45 GeV/c are economically described by a simple Regge model. A crucial feature of the model is the inclusion of a non-factorising pomeron which couples both to helicity flip and to non-flip. This allows an understanding of the observed t-dependent structure and rapid energy dependence of the pp polarisation. Predictions are made for pp and pn polarisation measurements at higher momenta. Fragmentary data on $\text{p}\text{p}$ elastic polarisation are compared to predictions.     

Comparison of exchange mechanisms in πN → ϱN and pion photo- and electroproduction

Pho-, photo- and electroproduction are compared and contrasted from a t-channel exchange point of view. A common exchange mechanism is evident. Systematic differences associated with the variable mass of the vector particle are found - in particular, the mass dependence of the non-pole-like contributions is reminiscent of that seen in higher mass resonance production. Naive vector meson dominance arguments which do not allow for these mass-dependent effects are shown to disagree both qualitatively and quantitatively with the data. We emphasize the implications of this, and similar studies, for an understanding of absorption effects in two-body scattering.