"Figure 2b Experimental Covariances" of "Measurement of the jet mass distribution and top quark mass in hadronic decays of boosted top quarks in pp collisions at $\sqrt{s} =$ 13 TeV"

A measurement is reported of the jet mass distribution in hadronic decays of boosted top quarks produced in \pp collisions at $\sqrt{s}=13\,\mathrm{TeV}$. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of $35.9\,\mathrm{fb}^{-1}$. The measurement is performed in the lepton+jets channel of $\mathrm{t}\overline{\mathrm{t}}$ events, where the lepton is an electron or muon. The products of the hadronic top quark decay $\mathrm{t} \rightarrow \mathrm{b}\mathrm{W} \rightarrow \mathrm{b}\mathrm{q}\mathrm{q}'$ are reconstructed as a single jet with transverse momentum larger than $400\,\mathrm{GeV}$. The $\mathrm{t}\overline{\mathrm{t}}$ cross section as a function of the jet mass is unfolded at the particle level and used to extract a value of the top quark mass of $172.6 \pm 2.5\,\mathrm{GeV}$. A novel jet reconstruction technique is used for the first time at the LHC, which improves the precision by a factor of three relative to an earlier measurement. This highlights the potential of measurements using boosted top quarks, where the new technique will enable future precision measurements.