Interpreting data from polarized proton beams

The reactions pp → pp and pp → Δ⁺⁺n with polarized beam and/or polarized target are currently under investigation at the Argonne ZGS. We discuss how to interpret various measured quantities in terms of amplitudes whose behavior is familiar (as functions of s, t). For pp total cross sections and elastic scattering, Argonne measurements will yield Im ?₂ (s,t = 0) and the rather complicated combination $\text{2|?}{}_5\text{|}{}^2\text{+}\text{Re}\text{(?}{}_1\text{?}{}_2{}^1\text{? ?}{}_3\text{?}{}_4{}^1\text{)}$, where ?_i (i = 1, … 5) are conventional s-channel helicity amplitudes. The forward direction (t = 0) is of special interest. We find that for both pp → pp and pp → Δ⁺⁺n, polarized beam — polarized target experiments plus the rather general (testable) assumption that amplitudes with the same s-channel helicity flip quantum numbers are proportional, are sufficient to fully determine all non-vanishing amplitudes at t = 0. Numerical estimates of some observables, based on calculations in a specific model, are also given.