Measurement of the jet mass distribution in highly boosted top quark decays in pp collisions at $\sqrt{s}=13~\text{TeV}$

A measurement of the jet mass distribution in highly boosted hadronic top quark decays produced in $\text{t}\bar{\text{t}}$ events from pp collisions at $\sqrt{s}=13~\text{TeV}$ is reported. The data were collected with the CMS detector at the LHC, and correspond to an integrated luminosity of $35.9~\text{fb}^{-1}$. The measurement is performed in the $\ell$+jets channel where $\ell$ is an electron or muon. The products of the fully hadronic decay $\text{t} \rightarrow \text{b}\text{W}$ with $\text{W}\rightarrow\text{q}\bar{\text{q}}'$ are reconstructed with a single jet with transverse momentum $p_\text{T}>400~\text{GeV}$. The $\text{t}\bar{\text{t}}$ cross section as a function of the jet mass is unfolded at the particle level and is used to extract a value of the top quark mass of $172.56 \pm 2.47~\text{GeV}$. This is the first measurement of the top quark mass in the highly boosted regime with a total uncertainty comparable to those from measurements performed at threshold $\text{t}\bar{\text{t}}$ production.