The optical model potential of the $\Sigma$ hyperon in nuclear matter

We present our attempts to determine the optical model potential $U_\Sigma = V_\Sigma -iW_\Sigma$ of the $\Sigma$ hyperon in nuclear matter. We analyze the following sources of information on $U_\Sigma$: $\Sigma N$ scattering, $\Sigma^-$ atoms, and final state interaction of $\Sigma$ hyperons in the $(\pi,K^+)$ and $(K^-.\pi)$ reactions on nuclear targets. We conclude that $V_\Sigma$ is repulsive inside the nucleus and has a shallow a tractive pocket at the nuclear surface. These features of $V_\Sigma$ are consistent with the Nijmegen model F of the hyperon-nucleon interaction.