  Twisted mass fermions allow light quarks to be explored but with the
consequence that there are mass splittings, such as between the neutral and
charged pion. Using a direct calculation of the connected neutral pion
correlator and stochastic methods to evaluate the disconnected correlations, we
determine the neutral pion mass. We explore the dependence on lattice spacing
and quark mass in quenched QCD. For dynamical QCD, we determine the sign of the
splitting which is linked, via chiral PT, to the nature of the phase transition
at small quark mass.
