In this pizza seminar I will present the measurement of quantum entanglement between a pair of top-quarks performed with the ATLAS detector which was recently published in Nature. I will review shortly the fundaments of top-quark spin measurements at proton-proton colliders with a couple of examples from previous measurements and I will discuss in more detail the new measurement that showed for the first time that top-quark pairs are produced in a entangled state close to the production threshold.
Giada Caneva, Elia Bertoldo, Francesco Sciotti