  Pi-Pi scattering is investigated for the first time for Nf=2+1+1 dynamical
quark flavours using Wilson twisted mass fermions. L\"uscher's finite size
method is used to relate energy shifts in finite volume to scattering
quantities like the scattering length in the I=2 channel. The computation is
performed at several pion masses and lattice spacings utilising the stochastic
LapH method.
