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arXiv:2309.08103

Testing Bell inequality through $h\toττ$ at CEPC

Kai Ma, Tong Li

Published Sep 15, 2023• 0 citations
arXivHTMLPDF

Abstract

The decay of Higgs boson into two spin-1/2 particles provides an ideal system to reveal quantum entanglement and Bell-nonlocality. Future $e^+e^-$ colliders can improve the measurement accuracy of the spin correlation of tau lepton pairs from Higgs boson decay. We show the testability of Bell inequality through $h\to ττ$ at Circular Electron Positron Collider (CEPC). Two realistic methods of testing Bell inequality are investigated, i.e., Törnqvist's method and Clauser-Home-Shimony-Holt (CHSH) inequality. In the simulation, we take into account the detector effects of CEPC including uncertainties for tracks and jets from $Z$ boson in the production of $e^+e^-\to Zh$. Necessary reconstruction approaches are described to measure quantum entanglement between $τ^+$ and $τ^-$. Finally, we show the sensitivity of CEPC to the Bell inequality violation for the two methods.

DOI
10.48550/arxiv.2309.08103

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Testing Bell inequality through h→ττh\toττh→ττ at CEPC
The decay of Higgs boson into two spin-1/2 particles provides an ideal system to reveal quantum entanglement and Bell-nonlocality. Future e+e−e^+e^-e+e− colliders can improve the measurement accuracy of the spin correlation of tau lepton pairs from Higgs boson decay. We show the testability of Bell inequality through h→ττh\to ττh→ττ at Circular Electron Positron Collider (CEPC). Two realistic methods of testing Bell inequality are investigated, i.e., Törnqvist's method and Clauser-Home-Shimony-Holt (CHSH) inequality. In the simulation, we take into account the detector effects of CEPC including uncertainties for tracks and jets from ZZZ boson in the production of e+e−→Zhe^+e^-\to Zhe+e−→Zh. Necessary reconstruction approaches are described to measure quantum entanglement between τ+τ^+τ+ and τ−τ^-τ−. Finally, we show the sensitivity of CEPC to the Bell inequality violation for the two methods.
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We study quantum entanglement and test violation of Bell-type inequality at the Circular Electron Positron Collider (CEPC), which is one of the most attractive future collides. It is a promising particle collider designed to search new physics, make Standard Model (SM) precision measurements, and serving as a Higgs factory. Our study is based on a fast simulation of the Z boson pair production from Higgs boson decay at s = 250 GeV . The detector effects are also included in the simulation. The spin density matrix of the joint Z Z system is parametrized using irreducible tensor operators and reconstructed from the spherical coordinates of the decay leptons. To test Bell inequalities, we construct observable quantities for the H → Z Z * process in CEPC by using the Collins-Gisin-Linden-Massar-Popescu (CGLMP) inequality, whose value is determined from the density matrix of the Z boson pairs. The sensitivity of the Bell inequality violation is observed with more than 1 σ and the presence of the quantum entanglement is probed with more than 2 σ confidence level.
Higgs boson decays produce pairs of W bosons in a maximally entangled state, the spins of which can be expected to violate Bell inequalities. We show that the spin density matrix of the W± pair may be reconstructed experimentally from the directions of the charged lepton decay products, and from it the expectation values of various Bell operators determined. Numerical simulations of H→WW⁎ decays indicate that violation of a generalised CHSH inequality is unlikely to be measurable, however the CGLMP inequality is near-maximally violated. Experimental Bell tests could be performed at a variety of colliders and in different production channels. If reconstruction effects and backgrounds can be controlled then statistically significant violations could be observable even with datasets comparable to those already collected at the LHC.
Higgs Boson Spookiness: Probing Quantum Nonlocality with Spacetime-Resolved H→τ+τ−H\rightarrowτ^+τ^-H→τ+τ− Decays
We demonstrate that a future precision eeeeee Higgs factory would be able to perform a spacetime-resolved test of quantum nonlocality in Higgs boson decays. In simulated ee→ZH→(μμ)(ττ)ee\rightarrow ZH \rightarrow (μμ)(ττ)ee→ZH→(μμ)(ττ) events at s=240\sqrt{s}=240s​=240 GeV, we reconstruct τττ lepton decay vertices and measure spin correlations as a function of the spacetime interval between the two τττ decays. Such a measurement would be able to test Bell-inequality-violating correlations for spacelike-separated decays, enabling direct exclusion of superluminal, finite-speed entanglement signaling theories. With 0.75 ab−1^{-1}−1 of integrated luminosity, entanglement signal propagation speeds below ≈2c\approx2c≈2c can be excluded at 95%\%% CL. Signals establishing any spin correlation can be excluded for speeds below ≈9c\approx9c≈9c. This constitutes the first proposed spacetime-resolved measurement of electroweak quantum entanglement at a particle collider and demonstrates a unique capability of future Higgs factories.
We introduce a methodology and investigate the feasibility of measuring quantum properties of tau lepton pairs in the $H\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ decay at future lepton colliders. In particular, observation of entanglement, steerability, and violation of Bell inequalities are examined for the International Linear Collider (ILC) and Future Circular ${e}^{+}{e}^{\ensuremath{-}}$ Collider (FCC-ee). We find that detecting quantum correlation crucially relies on precise reconstruction of the tau lepton rest frame, and a simple kinematics reconstruction does not suffice due to the finite energy resolution of the colliding beams and detectors. To correct for energy mismeasurements, a log-likelihood method is developed that incorporates the information of impact parameters of tau lepton decays. We demonstrate that an accurate measurement of quantum properties is possible with this method. As a by-product, we show that a novel model-independent test of CPCPCP violation can be performed and the CPCPCP phase of $H\ensuremath{\tau}\ensuremath{\tau}$ interaction can be constrained with an accuracy comparable to dedicated analyses, i.e., up to 7.9\ifmmode^\circ\else\textdegree\fi{} and 5.4\ifmmode^\circ\else\textdegree\fi{} at ILC and FCC-ee, respectively.
A bstract 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 → ZZ → 4 ℓ 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.