  Taking up and extending earlier suggestions, we show how two- and
threedimensional shapes of second-order HBT correlations can be described in a
multivariate Edgeworth expansion around gaussian ellipsoids, with expansion
coefficients, identified as the cumulants of pair momentum difference q, acting
as shape parameters. Off-diagonal terms dominate both the character and
magnitude of shapes. Cumulants can be measured directly and so the shape
analysis has no need for fitting.
