  A measurement of the mass difference between the top and the antitop quark
(Delta m(t) = m(t) - m(anti-t)) is performed using events with a muon or an
electron and at least four jets in the final state. The analysis is based on
data collected by the CMS experiment at the LHC, corresponding to an integrated
luminosity of 4.96 +/- 0.11 inverse femtobarns, and yields the value of Delta
m(t) = -0.44 +/- 0.46 (stat) +/- 0.27 (syst) GeV. This result is consistent
with equality of particle and antiparticle masses required by CPT invariance,
and provides a significantly improved precision relative to existing
measurements.
