  Two particle correlations are studied in the reaction plane of peripheral
relativistic heavy ion reactions where the initial state has substantial
angular momentum. The earlier predicted rotation effect and Kelvin Helmholtz
Instability, leads to space-time momentum correlations among the emitted
particles. A specific combination of two particle correlation measurements is
proposed, which can sensitively detect the rotation of the emitting system.
Here the method is presented in simple few source models where the symmetries
and the possibilities of the detection can be demonstrated in a transparent
way.
