A first measurement is presented of the top quark mass using the decay channel t to (W to l nu) (b to J/psi+X to mu+mu- + X), in events selected in proton-proton collisions and recorded with the CMS detector at the LHC at a center-of-mass energy of 8TeV. The data correspond to an integrated luminosity of 19.7 inverse femtobarns, with 666 ttbar and single top quark candidate events containing a reconstructed J/psi candidate decaying into an oppositely-charged muon pair. The mass of the (J/psi+l) system, where l is an electron or a muon from W boson decay, is used to extract a top quark mass of 173.5 +/- 3.0 (stat) +/- 0.9 (syst) GeVCMS Collaboration, "Measurement of the mass of the top quark in decays with a J/psi meson in pp collisions at 8 TeV" (August 11, 2016).
A combined margin of error of about +/- 3.13 GeV makes the new result almost useless, however, and even in a combined measurement, it would be weighted very minimally as a result of the lack of precision.
Still, the fact that the central result is quote close to the global average in a decay path not previously measured, does help make the existing estimate more robust and supports the integrity of the Standard Model in which the mass is calculated.