  Correlators between event planes of different harmonics in relativistic
heavy-ion collisions have the potential to provide crucial information on the
initial state of the matter formed in these collisions. We present a new
procedure for analyzing such correlators, which is less demanding in terms of
detector acceptance than the one used recently by the ATLAS collaboration to
measure various two-plane and three-plane correlators in Pb-Pb collisions at
LHC. It can also be used unambiguously for quantitative comparison between
theory and data. We use this procedure to carry out realistic simulations
within the transport model AMPT. Our theoretical results are in excellent
agreement with the ATLAS data, in contrast with previous hydrodynamic
calculations which only achieved qualitative agreement. We present predictions
for new correlators, in particular four-plane correlators, which can easily be
analyzed with our new method.
