  Residual correlations between decay products due to a combination of both
correlations between parents at small relative velocities and small decay
momenta are discussed. Residual correlations between photons from pion decays
are considered as a new possible source of information on direct photon
fraction. Residual correlations in $p\gamma$ and $p\Lambda$ systems due to
$p\Sigma^0$ interaction in final state are predicted based on the $p\Sigma^0$
low energy scattering parameters deduced from the spin-flavour SU$_6$ model by
Fujiwara et al. including effective meson exchange potentials and explicit
flavour symmetry breaking to reproduce the properties of the two-nucleon system
and the low-energy hyperon-nucleon cross section data. The $p\gamma_{\Sigma^0}$
residual correlation is concentrated at $k^* \approx 70$ Mev/$c$ and its shape
and intensity appears to be sensitive to the scattering parameters and
space-time dimensions of the source. The $p\Lambda_{\Sigma^0}$ residual
correlation recovers the negative parent $p\Sigma^0$ correlation for $k^* > 70$
Mev/$c$. The neglect of this negative residual correlation would lead to the
underestimation of the parent $p\Lambda$ correlation effect and to an
overestimation of the source size.
