Direct observation of the momentum distribution and renormalization factor in lithium

We have measured the momentum distribution and renormalization factor ${Z}_{{k}_F}$ in liquid and solid lithium by high-resolution Compton scattering. High-resolution data over a wide momentum range exhibit a clear feature of the renormalization and a sharp drop of momentum densities at the Fermi momentum ${k}_F$. These results are compared with those computed by quantum Monte Carlo simulation performed both on a disordered crystal and a liquid exhibiting very good agreement. Asymptotic behavior of the experimental and theoretical momentum distributions are examined to estimate ${Z}_{{k}_F}$. The experimentally obtained ${Z}_{{k}_F}=0.{43}_{\ensuremath{-}0.01}^+0.11$ for liquid Li and $0.{54}_{\ensuremath{-}0.02}^+0.11$ for solid Li are in good agreement with theoretical results of $0.54\ifmmode\pm\else\textpm\fi{}0.01$ and $0.64\ifmmode\pm\else\textpm\fi{}0.01$, respectively.