  Using effective theories for jets and heavy quarks it is possible to prove
that the double differential top-antitop invariant mass distribution for the
process $e^+e^-\to t\bar t$ in the resonance region for c.m. energies $Q$ much
larger than the top mass can factorized into perturbatively computable hard
coefficients and jet functions and a non-perturbative soft function. For
invariant mass prescriptions based on hemispheres defined with respect to the
thrust axis the soft function can be extracted from massless jet event shape
distributions. This approach allows in principle for top mass determinations
without uncertainties from hadronization using the reconstruction method and to
quantify the top mass scheme dependence of the measured top quark mass value.
