Measurement of the jet mass in highly boosted $${\mathrm{t}}\overline{\mathrm{t}}$$ t t ¯ events from pp collisions at $$\sqrt{s}=8$$ s = 8 $$\,\text {TeV}$$ TeV

Abstract

Abstract The first measurement of the jet mass $$m_{\text {jet}}$$ m jet of top quark jets produced in $${\mathrm{t}}\overline{\mathrm{t}} $$ t t ¯ events from pp collisions at $$\sqrt{s}=8$$ s = 8 $$\,\text {TeV}$$ TeV is reported for the jet with the largest transverse momentum $$p_{\mathrm{T}}$$ p T in highly boosted hadronic top quark decays. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.7 $$\,\text {fb}^{-1}$$ fb - 1 . The measurement is performed in the lepton+jets channel in which the products of the semileptonic decay $${\mathrm{t}} \rightarrow \mathrm{b} \mathrm {W}$$ t → b W with $$\mathrm {W}\rightarrow \ell \nu $$ W → ℓ ν where $$\ell $$ ℓ is an electron or muon, are used to select $${\mathrm{t}}\overline{\mathrm{t}} $$ t t ¯ events with large Lorentz boosts. The products of the fully hadronic decay $${\mathrm{t}} \rightarrow \mathrm{b} \mathrm {W}$$ t → b W with $$\mathrm {W}\rightarrow \mathrm{q} \overline{\mathrm{q}} '$$ W → q q ¯ ′ are reconstructed using a single Cambridge–Aachen jet with distance parameter $$R=1.2$$ R = 1.2 , and $$p_{\mathrm{T}} >400$$ p T > 400 $$\,\text {GeV}$$ GeV . The $${\mathrm{t}}\overline{\mathrm{t}} $$ t t ¯ cross section as a function of $$m_{\text {jet}}$$ m jet is unfolded at the particle level and is used to test the modelling of highly boosted top quark production. The peak position of the $$m_{\text {jet}}$$ m jet distribution is sensitive to the top quark mass $$m_{{\mathrm{t}}}$$ m t , and the data are used to extract a value of $$m_{{\mathrm{t}}}$$ m t to assess this sensitivity.

Keywords

• CMS
• Physics
• Top quark cross section
• Top quark mass