<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mi mathvariant="normal">D</mml:mi><mml:mover accent="true"><mml:mi mathvariant="normal">D</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:math> correlations as a sensitive probe for thermalization in high energy nuclear collisions