Testing entanglement and Bell inequalities in H-ZZ

We discuss quantum entanglement and violation of Bell inequalities in the H - ZZ decay, in particular when the two Z-bosons decay into light leptons. Although such process implies an important suppression of the statistics, this is traded by clean signals from a quasi maximally entangled system, which makes it very promising to check these crucial phenomena at high energy. In this paper we devise a novel framework to extract from H - ZZ data all significant information related to this goal, in particular spin correlation observables. In this context we derive sufficient and necessary conditions for entanglement in terms of only two parameters. Likewise, we obtain a sufficient and improved condition for the violation of Bell-type inequalities. The numerical analysis shows that with a luminosity of L = 300 fb-1 entanglement can be probed at > 3a level. For L = 3 ab-1 (HL-LHC) entanglement can be probed beyond the 5a level, while the sensitivity to a violation of the Bell inequalities is at the 4.5a level.

Automated summary

In this paper, we discuss quantum entanglement and violation of Bell inequalities in the H-ZZ decay, with a focus on the decay of the two Z-bosons into light leptons. We propose a novel framework to extract relevant information regarding these phenomena from the H-ZZ data, particularly spin correlation observables. We derive sufficient and necessary conditions for entanglement and an improved condition for the violation of Bell-type inequalities. Numerical analysis shows that entanglement can be probed at greater than 3a level with a luminosity of L = 300 fb-1. For L = 3 ab-1 (HL-LHC), entanglement can be probed beyond the 5a level, while the sensitivity to a violation of the Bell inequalities is at the 4.5a level.