Study of the quantum interference between singly and doubly resonant top-quark production in proton-proton collisions at the LHC with the ATLAS detector

The top quark is the heaviest known elementary particle of the Standard Model. Thanks to its particular properties, it allows to explore unique physics domains, inaccessible otherwise. One of them is the quantum interference between singly (tW) and doubly (t ̄t)resonant top quark production in proton-proton collisions, which can lead to identical WbWb final-states when an additional b-quark is radiated during a singly-resonant production. Studying this process is very important for a better knowledge of the Standard Model, but also to investigate some Beyond the Standard Model processes: for example,the search for top squarks suffers a large background contamination fromt W and t ̄t in the interference region. In this work, the measurement of the particle-level differential cross-section of the WbWb final-state in the eμ dilepton channel is provided, in order to better investigate the interference-sensitive region of these processes. The measurement is performed using the full dataset collected by the ATLAS detector from proton-proton collisions at the LHC during Run-2 at √s= 13 TeV corresponding to an integrated luminosity of 139 fb−1. The differential cross-section has been measured as a function of two interference-sensitive variables, defined as mminimaxbl and ∆R(b1,b2). Besides the single-differential cross-sections as a function of mminimaxbl and ∆R(b1,b2), also the double-differential cross-section as a function of mminimaxbl in bins of ∆R(b1,b2) is measured. The WbWb differential cross-section has been successfully extracted and compared to different schemes: the Diagram Removal and the Diagram Subtraction. This twopredictions model in a different way the quantum interference description.