  It is important to understand the strong external magnetic field generated at
the very beginning of high energy nuclear collisions. We study the effect of
the magnetic field on the charmonium yield and anisotropic distribution in
Pb+Pb collisions at the LHC energy. The time dependent Schr\"odinger equation
is employed to describe the motion of $c\bar{c}$ pairs. We compare our model
prediction of non- collective anisotropic parameter $v_2$ of $J/\psi$s with CMS
data at high transverse momentum. This is the first attempt to measure the
magnetic field in high energy nuclear collisions.
