  We measure the mass of the top quark in lepton+jets final states using the
full sample of $p\bar{p}$ collision data collected by the D0 experiment in
Run~II of the Fermilab Tevatron Collider at $\sqrt s=1.96~$TeV, corresponding
to $9.7~{\rm fb}^{-1}$ of integrated luminosity. We use a matrix element
technique that calculates the probabilities for each event to result from
$t\bar t$ production or background. The overall jet energy scale is constrained
in situ by the mass of the $W$ boson. We measure $m_t=174.98\pm0.76~{\rm GeV}$.
This constitutes the most precise single measurement of the top-quark mass.
