Search for top-squark pairs decaying into Higgs or Z bosons in pp collisions at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo>=</mml:mo><mml:mn>8</mml:mn><mml:mtext>TeV</mml:mtext></mml:math>
Physics letters. B