Magnetic fields and charm quarks in heavy-ion collisions

Under extreme conditions of high temperature and pressure, Quantum Chromodynamics predicts the formation of a new state of matter, the so-called Quark-Gluon Plasma (QGP). Heavy-ion collisions at ultra-relativistic energies at the Large Hadron Collider produce the optimal conditions to form the QGP in the laboratory. The hot QCD matter is produced within an unprecedented strong magnetic field, which properties and effects have not been yet fully explored. The magnetic field is early created in heavy-ion collisions by the charged spectator nucleons from the incident nuclei that do not participate in the collision. The charm quark is an ideal candidate to probe the properties of this magnetic field, because its formation time scale is comparable to the time scale when the magnetic field attains its maximum value and in addition the kinetic relaxation time of charm is similar to the QGP lifetime. Measuring the directed flow of D mesons will give access to early time dynamics, which are the least understood till now. The progress and status of the measurement of the D meson directed flow is shown. This measurement could be the first observation of an effect of the magnetic fields produced in heavy-ion collisions, which will shed light on fundamental and unexplored properties of the QGP (e.g. conductivity and initial density) and it will allow to constrain theoretical models.