External-magnetic-field-induced paramagnetic squeezing effect in heavy-ion collisions at energies available at the CERN Large Hadron Collider

In noncentral heavy-ion collisions, the quark-gluon plasma (QGP) encounters the most intense magnetic field ever produced in nature, with a strength of approximately similar to 1019-20 gauss. Recent lattice QCD calculations reveal that the QGP exhibits paramagnetic properties at high temperatures. When an external strong magnetic field is applied, it generates an anisotropic squeezing force density that competes with pressure gradients resulting from the purely QGP geometric expansion. In this study, we employ (3+1)-dimensional ideal hydrodynamics simulations to estimate the paramagnetic squeezing effect of this force density on the anisotropic expansion of QGP in noncentral Pb+Pb collisions at the Large Hadron Collider. We consider both up-to-date magnetic susceptibility and various magnetic field profiles in this work. We find that the impact of rapidly decaying magnetic fields is insignificant, while enduring magnetic fields produce a strong force density that diminishes the momentum anisotropy of the QGP by up to 10% at the intial stage, leaving a visible imprint on the elliptic flow v2 of final charged particles. Our results provide insights into the interplay between magnetic fields and the dynamics of QGP expansion in noncentral heavy-ion collisions.