A model-independent analysis of p + p --> pp(1S0) + gamma

The pp hard bremsstrahlung reaction, p + p --> pp(1S0) + gamma, in which the two protons in the final state are in the 1S0 state, is investigated theoretically. Here, the most general spin structure of the NN hard bremsstrahlung reaction, consistent with symmetry principles, is derived from a partial-wave expansion of this amplitude. Based on this spin structure, it is shown that there are only four independent spin matrix elements in this reaction, which is a direct consequence of reflection symmetry in the reaction plane. It is also shown that it requires at least eight independent observables to determine them uniquely. The present method provides the coefficients multiplying each spin operator in terms of the partial-wave or, equivalently, multipole amplitudes. Some observables are expressed explicitly in terms of these multipoles and a partial-wave analysis is performed. The results should be useful in the analyses of the experimental data on the p + p --> pp(1S0) + gamma reaction being taken, in particular, at the COSY accelerator facility, as well as in providing some theoretical guidance to the future experiments in this area.