  Recent measurements of resonance widths for low-energy neutron scattering off
heavy nuclei show large deviations from the standard Porter-Thomas
distribution. We propose a new resonance width distribution based on the random
matrix theory for an open quantum system. Two methods of derivation lead to a
single analytical expression; in the limit of vanishing continuum coupling, we
recover the Porter-Thomas distribution. The result depends on the ratio of
typical widths $\Gamma$ to the energy level spacing $D$ via the dimensionless
parameter $\kappa=(\pi\Gamma/2D)$. The new distribution suppresses small widths
and increases the probabilities of larger widths.
