Quantum information and <math display="inline"><mi>C</mi><mi>P</mi></math> measurement in <math display="inline"><mi>H</mi><mo stretchy="false">→</mo><msup><mi>τ</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>-</mo></msup></math> at future lepton colliders

Maltoni, Fabio;et.al.
(2023) Physical review D — Vol. 107 (2023)

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We introduce a methodology and investigate the feasibility of measuring quantum properties of tau lepton pairs in the <math display="inline"><mi>H</mi><mo stretchy="false">→</mo><msup><mi>τ</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>-</mo></msup></math> 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 <math display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>-</mo></msup></math> 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 <math display="inline"><mi>C</mi><mi>P</mi></math> violation can be performed and the <math display="inline"><mi>C</mi><mi>P</mi></math> phase of <math display="inline"><mi>H</mi><mi>τ</mi><mi>τ</mi></math> interaction can be constrained with an accuracy comparable to dedicated analyses, i.e., up to 7.9° and 5.4° at ILC and FCC-ee, respectively.
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Maltoni, F., & et al. (2023). Quantum information and <math display=“inline”><mi>C</mi><mi>P</mi></math> measurement in <math display=“inline”><mi>H</mi><mo stretchy=“false”>→</mo><msup><mi>τ</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>-</mo></msup></math> at future lepton colliders. Physical review D, 107. https://doi.org/10.1103/PhysRevD.107.093002 (Original work published 2023)