  We report the results of a theoretical study of quasielastic electron and
neutrino interactions with carbon. Our approach takes into account the effects
of final-state interactions between the struck nucleon and the residual
nucleus, neglected in the impulse approximation, through a generalization of
the spectral function formalism. The calculated electron-scattering cross
sections turn out to be in very good agreement with the available data over a
broad kinematical region. The impact of nuclear effects on the reconstruction
of neutrino energy in charged-current quasielastic processes is also studied,
and the results of our approach are compared to the predictions of the
relativistic Fermi gas model, routinely employed in most Monte Carlo
simulations. Finally, we discuss the limitations of the existing procedure for
energy reconstruction and propose a new, improved, one. At energy ~600 MeV, we
observe a sizable difference between neutrino and antineutrino scattering,
important for the measurements of charge-parity symmetry violation. Our
analysis suggests that a reliable determination of neutrino energy can only be
obtained from models validated by a systematic comparison to the available
electron-scattering data.
