Testing Bell inequalities and probing quantum entanglement at a muon collider

TL;DR

This paper explores the potential of a future muon collider to detect quantum entanglement and Bell inequality violations in Z boson pairs, demonstrating the feasibility through detailed simulations.

Contribution

It introduces a method to reconstruct the Z boson spin density matrix at a muon collider and tests Bell inequalities using this data, a novel approach in collider physics.

Findings

Maximal violation of the generalized CGLMP inequality is possible.

Bell inequalities can be tested with high statistical significance.

Quantum entanglement between Z bosons can be experimentally observed.

Abstract

A muon collider represents a promising candidate for the next generation of particle physics experiments after the expected end of LHC operations in the early 2040s. Rare or hard-to-detect processes at the LHC, such as the production of multiple gauge bosons, become accessible at a TeV muon collider. We present here the prospects of detecting quantum entanglement and the violation of Bell inequalities in H to ZZ to 4l events at a potential future muon collider. We show that the spin density matrix of the Z boson pairs can be reconstructed using the kinematics of the charged leptons from the Z boson decays. Once the density matrix is determined, it is straightforward to obtain the expectation values of various Bell operators and test the quantum entanglement between the Z boson pair. Through a detailed study based on Monte-Carlo simulation, we show that the generalized CGLMP inequality can be maximally violated, and testing Bell inequalities could be established with high significance.