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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.

The mass of the top quark is measured in 36.3$$\,\text {fb}^{-1}$$${\text{fb}}^{-1}$of LHC proton–proton collision data collected with the CMS detector at$$\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V} $$$\sqrt{s}=13\text{Te}\text{V}$. The measurement uses a sample of top quark pair candidate events containing one isolated electron or muon and at least four jets in the final state. For each event, the mass is reconstructed from a kinematic fit of the decay products to a top quark pair hypothesis. A profile likelihood method is applied using up to four observables per event to extract the top quark mass. The top quark mass is measured to be$$171.77\pm 0.37\,\text {Ge}\hspace{-.08em}\text {V} $$$171.77\pm 0.37\text{Ge}\text{V}$. This approach significantly improves the precision over previous measurements.

A search for high-mass dimuon resonance production in association with one or more b quark jets is presented. The study uses proton-proton collision data collected with the CMS detector at the LHC corresponding to an integrated luminosity of 138 fb⁻¹at a center-of-mass energy of 13 TeV. Model-independent limits are derived on the number of signal events with exactly one or more than one b quark jet. Results are also interpreted in a lepton-flavor-universal model with Z′ boson couplings to a bb quark pair (g_b), an sb quark pair (g_bδ_bs), and any same-flavor charged lepton (g_ℓ) or neutrino pair (g_ν), with|g_ν|=|g_ℓ|. For a Z′ boson with a mass$$ {m}_{{\textrm{Z}}^{\prime }} $$$m_{Z^{\prime }}$= 350 GeV (2 TeV) and|δ_bs|< 0.25, the majority of the parameter space with 0.0057 <|g_ℓ|< 0.35 (0.25 <|g_ℓ|< 0.43) and 0.0079 < |g_b| < 0.46 (0.34 < |g_b| < 0.57) is excluded at 95% confidence level. Finally, constraints are set on a Z′ model with parameters consistent with low-energy b → sℓℓmeasurements. In this scenario, most of the allowed parameter space is excluded for a Z′ boson with 350 <$$ {m}_{{\textrm{Z}}^{\prime }} $$$m_{Z^{\prime }}$< 500 GeV, while the constraints are less stringent for higher$$ {m}_{{\textrm{Z}}^{\prime }} $$$m_{Z^{\prime }}$hypotheses. This is the first dedicated search at the LHC for a high-mass dimuon resonance produced in association with multiple b quark jets, and the constraints obtained on models with this signature are the most stringent to date.

The second-order (v₂) and third-order (v₃) Fourier coefficients describing the azimuthal anisotropy of prompt and nonprompt (from b-hadron decays) J/ψ, as well as prompt ψ(2S) mesons are measured in lead-lead collisions at a center-of-mass energy per nucleon pair of$$ \sqrt{s_{\textrm{NN}}} $$$\sqrt{s_{\mathrm{NN}}}$= 5.02 TeV. The analysis uses a data set corresponding to an integrated luminosity of 1.61 nb⁻¹recorded with the CMS detector. The J/ψ and ψ(2S) mesons are reconstructed using their dimuon decay channel. Thev₂andv₃coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measuredv₂values for prompt J/ψ mesons are found to be larger than those for nonprompt J/ψ mesons. The prompt J/ψv₂values at highp_Tare found to be underpredicted by a model incorporating only parton energy loss effects in a quark-gluon plasma medium. Prompt and nonprompt J/ψ mesonv₃and prompt ψ(2S)v₂andv₃values are also reported for the first time, providing new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions.