Paramagnetic squeezing of QCD matter

We determine the magnetization of Quantum Chromodynamics (QCD) for several temperatures around and above the transition between the hadronic and the quark-gluon phases of strongly interacting matter. We obtain a paramagnetic response that increases in strength with the temperature. We argue that due to this paramagnetism, chunks of quark-gluon plasma produced in non-central heavy ion collisions should become elongated along the direction of the magnetic field. This anisotropy will then contribute to the elliptic flow v_2 observed in such collisions, in addition to the pressure gradient that is usually taken into account. We present a simple estimate for the magnitude of this new effect and a rough comparison to the effect due to the initial collision geometry. We conclude that the paramagnetic effect might have a significant impact on the value of v_2.