  Current measurements of the top quark mass which have achieved a precision of
less than 1 GeV involve a theoretical problem that the definition of the
measured mass is ambiguous in perturbation theory. As a possible solution to
the problem, we present a new method to measure the top quark mass at the LHC.
This method uses lepton energy distribution and has a boost-invariant nature.
We discuss strategies towards a precise determination of theoretically
well-defined top quark masses such as the MSbar mass with the method. As a
first step in this direction, a simulation analysis at the leading order is
performed considering actual experimental circumstances. The result indicates
that this method with further improvements is capable of realizing a precision
of less than 1 GeV at the LHC.
