  We present a first Wilson twisted mass fermion calculation of the matrix
element between pion states of the twist-2 operator, which is related to the
the lowest moment < x > of the valence quark parton distribution function in a
pion. Using Wilson twisted mass fermions in the quenched approximation we
demonstrate that < x > can be computed at small pseudoscalar meson masses down
to values of order 250 MeV. We investigate the scaling behaviour of this
physically important quantity by applying two definitions of the critical mass
and observe a scaling compatible with the expected O(a^2) behaviour in both
cases. A combined continuum extrapolation allows to obtain reliable results for
< x > at very small pseudoscalar meson masses, which previously could not be
explored by lattice QCD simulations.
