The $pp \to nK^+\Sigma^+$ reaction is a very good isospin 3/2 filter for studying $\Delta^{ ++*}$ decaying to $K^+\Sigma^+$. With an effective Lagrangian approach, contributions from a previous ignored sub-$K^+\Sigma^+$-threshold resonance $\Delta^{ ++*}(1620)1/2^-$ are fully included in addition to those already considered in previous calculations. It is found that the $\Delta^{ ++*}(1620)1/2^-$ resonance gives an overwhelmingly dominant contribution for energies very close to threshold, with a very important contribution from the t-channel $\rho$ exchange. This solves the problem that all previous calculations seriously underestimate the near-threshold cross section by order(s) of magnitude. Many important implications of the results are discussed.
Categories: nucl-th