Measurements of Hadronic $t\overline{t}$ Differential Cross Sections with ATLAS and Unfolding with Gaussian Processes

Measurements of $t\overline{t}$ production cross sections at the Large Hadron Collider are presented. Proton–proton collision data with a centre-of-momentum energy of 13 TeV were collected using the ATLAS detector, totalling an integrated luminosity of 36.1 fb$^{-1}$. The measurements are performed for the fully hadronic decay channel where the jets can be resolved. This allows all $t\overline{t}$ decay components to be measured along with additional QCD radiation. The results are presented as absolute and normalised unfolded differential cross sections at particle level, as functions of several kinematic variables. Some cross sections are also unfolded to parton level, and some two-dimensional differential cross sections are presented. These distributions are compared to several Monte Carlo simulations. Potential uses for Gaussian processes in particle physics are discussed, and a novel method for unfolding with Gaussian processes is introduced. The method is derived and assessed in terms of the unfolded estimators, statistical covariance matrices, and flexibility of the model.