We propose a new method to measure a theoretically well-defined top quark mass at the LHC. This method is based on the weight function method, which we proposed in our preceding paper. It requires only lepton energy distribution and is basically inde
pendent of the production process of the top quark. We perform a simulation analysis of the top quark mass reconstruction with $tbar{t}$ pair production and lepton+jets decay channel at the leading order. The estimated statistical error of the top quark mass is about $0.4$ GeV with an integrated luminosity of $100$ fb$^{-1}$ at $sqrt{s}=14$ TeV. We also estimate some of the major systematic uncertainties and find that they are under good control.
