## Measurements of top-quark pair to $$Z$$-boson cross-section ratios at $$\sqrt{s}$$ $$=13 , 8, 7$$ TeV with the ATLAS detector

Please always quote using this URN: urn:nbn:de:bvb:20-opus-173544

• Ratios of top-quark pair to $$Z$$-boson cross sections measured from proton-proton collisions at the LHC centre-of-mass energies of $$\sqrt{s}$$ = 13 TeV, 8 TeV, and 7 TeV are presented by the ATLAS Collaboration. Single ratios, at a given $$\sqrt{s}$$ for the two processes and at different $$\sqrt{s}$$ for each process, as well as double ratios of the two processes at different $$\sqrt{s}$$, are evaluated. The ratios are constructed using previously published ATLAS measurements of the $${t\overline{t}}$$ and $$Z$$-boson production crossRatios of top-quark pair to $$Z$$-boson cross sections measured from proton-proton collisions at the LHC centre-of-mass energies of $$\sqrt{s}$$ = 13 TeV, 8 TeV, and 7 TeV are presented by the ATLAS Collaboration. Single ratios, at a given $$\sqrt{s}$$ for the two processes and at different $$\sqrt{s}$$ for each process, as well as double ratios of the two processes at different $$\sqrt{s}$$, are evaluated. The ratios are constructed using previously published ATLAS measurements of the $${t\overline{t}}$$ and $$Z$$-boson production cross sections, corrected to a common phase space where required, and a new analysis of $$Z$$ → ℓ$$^+$$ℓ$$^-$$ where ℓ = $$e, µ$$ at $$\sqrt{s}$$ = 13 TeV performed with data collected in 2015 with an integrated luminosity of 3.2 fb$$^−1$$. Correlations of systematic uncertainties are taken into account when evaluating the uncertainties in the ratios. The correlation model is also used to evaluate the combined cross section of the $$Z$$ → $$e$$$$^+$$$$e$$$$^−$$ and the $$Z$$ → $$µ$$$$^+$$$$µ$$$$^−$$ channels for each $$\sqrt{s}$$ value. The results are compared to calculations performed at next-to-next-to-leading-order accuracy using recent sets of parton distribution functions. The data demonstrate significant power to constrain the gluon distribution function for the Bjorken-$$x$$ values near 0.1 and the light-quark sea for $$x$$ < 0.02.