Measurement of the top-antitop mass difference

The standard model of particle physics is a local gauge-invariant quantum field theory in which the CPT symmetry plays a fundamental role. One of the consequences of CPT invariance is an equal mass for a particle and its antiparticle. In order to test the CPT invariance, we performed a measurement of the mass difference between the top and the antitop quark ($\Delta m_{\text{t}} = m_{\mathrm{t}} - m_{\overline{\mathrm{t}}}$) 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 $4.96 \pm 0.11$~fb$^{-1}$, and yields the value of $\Delta m_{\text{t}} = -0.44 \pm 0.46 ~(\text{stat.}) \pm 0.27 ~(\text{syst.})~\text{GeV}$. 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.