Direct reconstruction of isosinglet amplitudes for nucleon-nucleon elastic scattering

The direct reconstruction of the isospin I = 0 amplitudes is discussed under the assumption that the I = 1 amplitudes are known and that a sufficient number of independent np observables have been measured at a centre-of-mass angle theta. The show that at least one observable measured at angle pi - theta is necessary in order to determine the I = 0 amplitudes, including the phase relative to the I = 1 amplitudes. Special cases at theta = 0; pi/2 and pi are also discussed.