Quantum tops at the LHC: from entanglement to Bell inequalities

TL;DR

This paper explores the feasibility of detecting quantum entanglement and Bell inequality violations in top quark pair events at the LHC, finding entanglement detectable but Bell violations challenging.

Contribution

It introduces new observables for entanglement and Bell tests in LHC data and assesses their experimental detectability using simulations.

Findings

Entanglement detectable at >5σ in current LHC data.

Bell inequality violation detection requires very high-$p_T$ events.

Testing Bell inequalities at the LHC is more challenging than previously estimated.

Abstract

We present the prospects of detecting quantum entanglement and the violation of Bell inequalities in $t\bar{t}$ 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$\sigma$ both at threshold as well as at high $p_T$ already in the LHC Run 2 dataset. On the other hand, only very high-$p_T$ 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.