Measurement of the jet mass distribution in boosted $\mathrm{t}\bar{\mathrm{t}}$ production at $\sqrt{s}=8~\mathrm{TeV}$

A first measurement is performed of the differential $\mathrm{t}\bar{\mathrm{t}}$ production cross section as a function of the leading jet mass in fully-merged top quark decays. Data collected with the CMS detector in pp collisions at $\sqrt{s}=8$ TeV are used, corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The measurement is carried out in the $\ell$+jets channel, where the products of the leptonic decay are used to select $\mathrm{t}\bar{\mathrm{t}}$ events with high Lorentz boosts. The products of the hadronic decay are reconstructed with a single Cambridge/Aachen jet with distance parameter $R=1.2$, and transverse momentum $p_{\mathrm{T}}>400$ GeV. The cross section, as a function of the jet mass $m_{\rm{jet}}$, is unfolded and reported on particle level. The measurement is used to test the modelling of boosted top quark production. The peak position of the $m_{\rm{jet}}$ distribution is sensitive to the top quark mass $m_\text{t}$ and the data are used to extract a value of $m_\text{t}$ to assess the measurement's sensitivity.