Abstract
Quantum entanglement is a fundamental property of quantum mechanics. Recently, studies have explored entanglement in the \( t\overline{t} \) system at the Large Hadron Collider (LHC) when both the top quark and anti-top quark decay leptonically. Entanglement is detected via correlations between the polarizations of the top and anti-top and these polarizations are measured through the angles of the decay products of the top and anti-top. In this work, we propose searching for evidence of quantum entanglement in the semi-leptonic decay channel where the final state includes one lepton, one neutrino, two b-flavor tagged jets, and two light jets from the W decay. We find that this channel is both easier to reconstruct and has a larger effective quantity of data than the fully leptonic channel. As a result, the semi-leptonic channel is 60% more sensitive to quantum entanglement and a factor of 3 more sensitive to Bell inequality violation, compared to the leptonic channel. In 139 fb−1 (3 ab−1) of data at the LHC (HL-LHC), it should be feasible to measure entanglement at a precision of ≲ 3% (0.7%). Detecting Bell inequality violation, on the other hand, is more challenging. With 300 fb−1 (3 ab−1) of integrated luminosity at the LHC Run-3 (HL-LHC), we expect a sensitivity of 1.3σ (4.1σ). In our study, we utilize a realistic parametric fitting procedure to optimally recover the true angular distributions from detector effects. Compared to unfolding this procedure yields more stable results.
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Acknowledgments
The authors would like to thank Mikael Kuusela for detailed discussion on unfolding, Joseph Boudreau and Kun Cheng for useful discussions, and Ze Chen for computing assistance. This work was supported in part by the U.S. Department of Energy under grant Nos. DESC0007914 and in part by the Pitt PACC. TH would like to thank the Aspen Center for Physics, where part of this work is complete, which is supported by the National Science Foundation (NSF) grant PHY-1607611. ML is also supported by the National Science Foundation under grant no. PHY-2112829.
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Han, T., Low, M. & Wu, T.A. Quantum entanglement and Bell inequality violation in semi-leptonic top decays. J. High Energ. Phys. 2024, 192 (2024). https://doi.org/10.1007/JHEP07(2024)192
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DOI: https://doi.org/10.1007/JHEP07(2024)192