  We propose a new method to measure various physical parameters, using
characteristic weight functions. This method requires only lepton energy
distribution and ideally it does not depend on the velocity of the parent
particle. We demonstrate an application of this method by simulating a
reconstruction of the Higgs boson mass in the H-> WW -> lnu lnu decay mode at
the LHC. We show that systematic errors are suppressed compared to statistical
errors. In the vector boson fusion channel, the statistical accuracy of the
mass determination is estimated to be +12% and -14% at an integrated luminosity
of 100fb^{-1}, assuming the Higgs boson mass to be 125GeV and root{s}=14TeV.
