  The invariance of the standard model (SM) under the CPT transformation
predicts equality of particle and antiparticle masses. This prediction is
tested by measuring the mass difference between the top quark and antiquark
(Delta m[t] = m[t] - m[t-bar]) that are produced in pp collisions at a
center-of-mass energy of 8 TeV, using events with a muon or an electron and at
least four jets in the final state. The analysis is based on data corresponding
to an integrated luminosity of 19.6 inverse femtobarns collected by the CMS
experiment at the LHC, and yields a value of Delta m[t] = -0.15 +/- 0.19 (stat)
+/- 0.09 (syst) GeV, which is consistent with the SM expectation. This result
is significantly more precise than previously reported measurements.
