  We apply black-box methods, i.e. where the performance of the method does not
depend upon initial guesses, to extract excited-state energies from
Euclidean-time hadron correlation functions. In particular, we extend the
widely used effective-mass method to incorporate multiple correlation functions
and produce effective mass estimates for multiple excited states. In general,
these excited-state effective masses will be determined by finding the roots of
some polynomial. We demonstrate the method using sample lattice data to
determine excited-state energies of the nucleon and compare the results to
other energy-level finding techniques.
