Characterization of the quantum state of top quark pairs produced in proton-proton collisions at <math display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> using the beam and helicity bases

Petersen, Henriette;Bein, Samuel;Benecke, Anna;Bethani, Agni;CMS;et.al.
(2026) Physical review D — Vol. 113 (2026)

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Abstract
Measurements of the spin correlation coefficients in the beam basis are presented for top quark-antiquark (<math display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math>) systems produced in proton-proton collisions at <math display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> collected by the CMS experiment in 2016–2018, and corresponding to an integrated luminosity of <math display="inline"><mn>138</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>-</mo><mn>1</mn></mrow></msup></math>. The <math display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math> system is reconstructed from final states containing an electron or muon and jets. Together with the previously reported results in the helicity basis, these measurements are used to decompose the system into the Bell and spin eigenstates in various kinematic regions. The spin correlation coefficients are also used to evaluate properties of the <math display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math> quantum state, such as the purity, von Neumann entropy, and entanglement. All results are consistent with standard model predictions.
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Petersen, H., Bein, S., Benecke, A., Bethani, A., Bruno, G., Cappati, A., de Favereau de Jeneret, J., Delaere, C., Gameiro Casalinho, F., Giammanco, A., Guzel, A. O., Lemaitre, V., Lidrych, J., Malek, P., Mastrapasqua, P., Turkcapar, S., CMS, & et al. (2026). Characterization of the quantum state of top quark pairs produced in proton-proton collisions at <math display=“inline”><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> using the beam and helicity bases. Physical review D, 113. https://doi.org/10.1103/hkgw-dztk (Original work published 2026)