Form Factors, Kronecker-δTerms, and the Absorptive Peripheral Model

A prescription (OPE-$\delta$) is introduced which enables one to obtain with little effort approximate results of absorption-model calculations for spin-space density matrix elements of unstable particles produced in high-energy quasi-two-body inelastic reactions. The OPE-$\delta$ method does not involve a partial-wave expansion. It consists of dropping those parts of the OPE amplitudes which would otherwise lead to Kronecker-$\delta$ contributions to the partial-wave amplitudes. The method is partially justified by studying results of one-pion-exchange-absorption calculations with and without form factors. Explicit calculations are presented for the reaction ${\pi }^{-}+p\to {\rho }^{-}+p$ at 3 BeV/c.