Squeezed fermions at relativistic heavy ion colliders

Large back-to-back correlations of observable fermion-anti-fermion pairs ar e predicted to appear, if the mass of the fermions is modified in a thermal ized medium. The back-to-back correlations of protons and anti-protons are experimentally observable in ultra-relativistic heavy ion collisions, simil arly to the Andreev reflection of elections off the boundary of a supercond uctor. While quantum statistics suppresses the probability of observing pai rs of fermions with nearby momenta, the fermionic back-to-back correlations are positive and of similar strength to bosonic back-to-back correlations. (C) 2001 Elsevier Science B,V, All rights reserved.