Directed Flow of Charm Quarks induced by the Initial Magnetic Field at LHC

Santosh K. Das, Salvatore Plumari, Sandeep Chatterjee, Jane Alam, Francesco Scardina, Vincenzo Greco

Published 2016-08-07Version 1

The ultra-relativistic Heavy-Ion Collisions generate a very strong initial magnetic field $\vec B$ inducing a vorticity in the reaction plane. While the magnetic field would determine a very large effect, its time dependence induce also a large electric field $\vec E$ that leads to a Faraday current that counteracts the Hall drift of the $\vec B$ field. We show that the final effect anyway entails a directed flow $v_1$ of charm quarks that is still significantly large due to a combination of favourable conditions for charm quarks: their formation time $\tau_f \simeq \, 0.1 \rm fm/c$ matches the maximum of the $\vec B$ field and a kinetic relaxation time comparable with the QGP lifetime $\tau_{eq} \approx \tau_{QGP}$ that allows to keep the initial kick in the transverse direction. The effect is also odd under charge exchange allowing to distinguish it from the vorticity of the bulk matter due to the initial angular momentum conservation; conjointly thanks to their mass $M_c >> \Lambda_{QCD}$ there should be no mixing with the chiral magnetic dynamics, therefore, charm quarks can supply a fundamental independent information on the strength of the magnetic field.