A low Energy $t\bar{t}$ Cross-section Measurement with the ATLAS Detector

The inclusive top-quark pair (tt ̅) production cross-section was measured in proton-proton collisions at a center of mass energy of 5 TeV with 257 pb^(-1) of data collected by the ATLAS detector. The tt ̅ cross-section measurement at a lower center of mass helps to further constrain the gluon Parton Distribution Function (PDF) at high Bjorken x. The cross-section is first measured individually in both the dilepton and single-lepton channels of the tt ̅ decay before being combined. The measurement in the dilepton channel is measured using a “cut-and-count” approach whereas the single-lepton measurement utilizes a Boosted Decision Tree (BDT) trained on Monte Carlo to separate signal from background. The output distribution of the BDT is the fit to data in a profile-likelihood fit leading to the single-lepton measurement being the most precise measurement of the tt ̅ cross-section measured in the single-lepton channel to date.