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AbstractThe inclusive top quark pair ($$t\bar{t}$$ t t ¯ ) production cross-section $$\sigma _{t\bar{t}}$$ σ t t ¯ has been measured in proton–proton collisions at $$\sqrt{s}=13\,\text {TeV}$$ s = 13 TeV , using 36.1 fb$$^{-1}$$ - 1 of data collected in 2015–2016 by the ATLAS experiment at the LHC. Using events with an opposite-charge $$e\mu $$ e μ pair and b-tagged jets, the cross-section is measured to be: $$\begin{aligned} \sigma _{t\bar{t}} = 826.4 \pm 3.6\,\mathrm {(stat)}\ \pm 11.5\,\mathrm {(syst)}\ \pm 15.7\,\mathrm {(lumi)}\ \pm 1.9\,\mathrm {(beam)}\,\mathrm {pb}, \end{aligned}$$ σ t t ¯ = 826.4 ± 3.6 ( stat ) ± 11.5 ( syst ) ± 15.7 ( lumi ) ± 1.9 ( beam ) pb , where the uncertainties reflect the limited size of the data sample, experimental and theoretical systematic effects, the integrated luminosity, and the LHC beam energy, giving a total uncertainty of 2.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. It is used to determine the top quark pole mass via the dependence of the predicted cross-section on $$m_t^{\mathrm{pole}}$$ m t pole , giving $$m_t^{\mathrm{pole}}=173.1^{+2.0}_{-2.1}\,\text {GeV}$$ m t pole = 173 . 1 - 2.1 + 2.0 GeV . It is also combined with measurements at $$\sqrt{s}=7\,\text {TeV}$$ s = 7 TeV and $$\sqrt{s}=8\,\text {TeV}$$ s = 8 TeV to derive ratios and double ratios of $$t\bar{t}$$ t t ¯ and Z cross-sections at different energies. The same event sample is used to measure absolute and normalised differential cross-sections as functions of single-lepton and dilepton kinematic variables, and the results are compared with predictions from various Monte Carlo event generators.

ABSTRACTIn the search for the mechanisms involved in the immobilization of organic nitrogen in humified remains of vascular plants, the efforts of the present investigation were directed toward the examination of the transformation of nitrogenous compounds during the peat and coal stage by means of solid‐state nuclear magnetic resonance (NMR) spectroscopy. While accumulation of heteroaromatic‐N is not detected in most of the studied peat layers, a clear shoulder in the chemical shift region of pyrrole‐ or indole‐N is observed in the solid‐state 15N NMR spectrum of material from the deepest (and thus oldest) peat layer underlying the sapropel from Mangrove Lake, Bermuda (10000 years). This points to the assumption that transformation of nitrogen occurs between an advanced stage of peatification and an early stage of coalification. The observed sudden alteration in nitrogen functionality indicates that continuous accumulation of newly synthesized or selectively preserved biogenic structures is not responsible for the presence of heteroaromatic‐N in these fossilized deposits. It seems rather likely that abiotic conditions, occurring during advanced sediment maturation, have an effect on the observed N transformation. With increasing coalification, pyrrole‐type‐N becomes the dominant form in the macromolecular coal network. Pyridine‐type‐N was only detected in a coal of anthracite rank.