Unfolding the top: Measuring the quantum interference between singly and doubly resonant top-quark production at $\sqrt{s} = 13$ TeV with the ATLAS detector

The production of top-quark pairs $t\bar{t}$ is extensively studied at the Large Hadron Collider (LHC) due to its importance in probing fundamental parameters of the Standard Model (SM) and its role as a background in various searches for physics Beyond the Standard Model (BSM). In particular in conjunction with ttbar, single-top is also an important process in measurements and searches, but less studied and more challenging to treat theoretically. This analysis tries to fill this gap, by measuring the cross-section of $WbWb$, which is a final state of both $t\bar{t}$ and single-top processes. While the $t\bar{t}$ and $tW$ are commonly treated as independent processes, the presented analysis addresses the interference effects between them, which become particularly relevant at higher orders in perturbative QCD, providing a more consistent theoretical treatment. The analysis uses semileptonic $WbWb$ decays and thereby is complementary to an ATLAS result in the dilepton channel. To improve the modelling in a broad phase-space, two measurement regions are defined: one encompassing the majority of events to have the largest accessible cross-section, and another targeting the tails of distributions to explore phase spaces relevant to BSM searches. These differential cross-section measurements are valuable for assessing and tuning Monte Carlo generators, determining SM parameters, and constraining uncertainties in BSM searches. Utilizing the full dataset from the ATLAS detector at $\sqrt{s} = 13 $ TeV with $ \mathcal{L} = 140\, \text{fb}^{-1} $ collected in Run-2, this study contributes to a more comprehensive understanding of top-quark pair production and its implications for future physics searches.