Quantum tops at the LHC: from entanglement to Bell inequalities

Abstract

We present the prospects of detecting quantum entanglement and the violation of Bell inequalities in tt¯ events at the LHC. We introduce a unique set of observables suitable for both measurements, and then perform the corresponding analyses using simulated events in the dilepton final state, reconstructing up to the unfolded level. We find that entanglement can be established at better than 5 σ both at threshold as well as at high pT already in the LHC Run 2 dataset. On the other hand, only very high-pT events are sensitive to a violation of Bell inequalities, making it significantly harder to observe experimentally. By employing a sensitive and robust observable, two different unfolding methods and independent statistical approaches, we conclude that, at variance with previous estimates, testing Bell inequalities will be challenging even in the high luminosity LHC run.