  We present results of dynamical simulations with 2 flavours of degenerate
Wilson twisted mass quarks at maximal twist in the range of pseudo scalar
masses from 300 to 550 MeV. The simulations are performed at one value of the
lattice spacing a \lesssim 0.1 fm. In order to have O(a) improvement and aiming
at small residual cutoff effects, the theory is tuned to maximal twist by
requiring the vanishing of the untwisted quark mass. Precise results for the
pseudo scalar decay constant and the pseudo scalar mass are confronted with
chiral perturbation theory predictions and the low energy constants F,
\bar{l}_3 and \bar{l}_4 are evaluated with small statistical errors.
