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

LHCC 2017 POSTER. Ratios of top-quark pair to Z-boson cross sections measured at the LHC centre-of-mass energies of $\sqrt{s} = 13~\text{TeV}, 8~\text{TeV}, 7~\text{TeV}$ using data collected with an integrated luminosity of $3.2~\text{fb}^{−1}$, $20.2~\text{fb}^{−1}$, $4.6~\text{fb}^{−1}$, respectively. 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. Correlation of systematic uncertainties are used for uncertainties calculation in the ratios. The data demonstrate significant power to constrain the gluon distribution function for the Bjorken-x $\sim$ 0.1.