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A description is presented of the algorithms used to reconstruct energy deposited in the CMS hadron calorimeter during Run 2 (2015–2018) of the LHC. During Run 2, the characteristic bunch-crossing spacing for proton-proton collisions was 25 ns, which resulted in overlapping signals from adjacent crossings. The energy corresponding to a particular bunch crossing of interest is estimated using the known pulse shapes of energy depositions in the calorimeter, which are measured as functions of both energy and time. A variety of algorithms were developed to mitigate the effects of adjacent bunch crossings on local energy reconstruction in the hadron calorimeter in Run 2, and their performance is compared.

 

Abstract A measurement of the jet mass distribution in hadronic decays of Lorentz-boosted top quarks is presented. The measurement is performed in the lepton + jets channel of top quark pair production ( $$\hbox {t}\overline{\hbox {t}}$$ t t ¯ ) events, where the lepton is an electron or muon. The products of the hadronic top quark decay are reconstructed using a single large-radius jet with transverse momentum greater than 400 $$\,\text {Ge}\hspace{-.08em}\text {V}$$ Ge V . The data were collected with the CMS detector at the LHC in proton-proton collisions and correspond to an integrated luminosity of 138 $$\,\text {fb}^{-1}$$ fb - 1 . The differential $$\hbox {t}\overline{\hbox {t}}$$ t t ¯ production cross section as a function of the jet mass is unfolded to the particle level and is used to extract the top quark mass. The jet mass scale is calibrated using the hadronic W boson decay within the large-radius jet. The uncertainties in the modelling of the final state radiation are reduced by studying angular correlations in the jet substructure. These developments lead to a significant increase in precision, and a top quark mass of $$173.06 \pm 0.84\,\text {Ge}\hspace{-.08em}\text {V} $$ 173.06 ± 0.84 Ge V .