Bell Inequalities and Quantum Correlations in $H \rightarrow ZZ \rightarrow 2e\,2\mu$

TL;DR

This study uses CMS open data to analyze quantum entanglement in Higgs boson decays to Z bosons, demonstrating the presence of quantum correlations in signal events and their absence in background, thus testing fundamental quantum mechanics at colliders.

Contribution

First application of Bell inequality tests to Higgs decay data, incorporating realistic detector effects and quantifying entanglement in high-energy particle processes.

Findings

Signal events show Bell parameter I_3 > 2, indicating entanglement.

Background events have I_3 < 2, indicating no entanglement.

Results demonstrate feasibility of quantum tests at high energy colliders.

Abstract

We investigate quantum correlations in Higgs-boson decays $\bigl(H \rightarrow ZZ^* \rightarrow 2e\,2\mu\bigr)$ using CMS open data at $\sqrt{s}$ = 8 TeV, incorporating realistic detector effects. By reconstructing the polarization density matrix of the two-boson system and evaluating the Collins-Gisin-Linden-Massar-Popescu (CGLMP) Bell operator $I_3$, we quantify entanglement in the $ZZ$ state. Our analysis yields an $I_3$ value of $2.152 \pm 0.003$ for signal events $\bigl(H \rightarrow ZZ^*\bigr)$, indicating the presence of quantum entanglement. The non-resonant continuum background events $\bigl(pp \rightarrow ZZ\bigr)$ yield $I_3 = 1.158 \pm 0.012$, suggesting the absence of quantum correlations. These results demonstrate the feasibility of testing fundamental quantum mechanics at high energy colliders.