Entanglement is an intrinsic property of quantum mechanics and is predicted to be exhibited in the particles produced at the Large Hadron Collider. A measurement of the extent of entanglement in top quark-antiquark (t tbar) events produced in proton-proton collisions at a center-of-mass energy of 13 TeV is performed with the data recorded by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 36.3 fb−1. The events are selected based on the presence of two leptons with opposite charges and high transverse momentum. An entanglement-sensitive observable D is derived from the top quark spin-dependent parts of the t tbar production density matrix and measured in the region of the t tbar production threshold. Values of D < − 1 / 3 are evidence of entanglement and D is observed (expected) to be −0.480 −0.029 +0.026 (−0.467 −0.029 +0.026) at the parton level. With an observed significance of 5.1 standard deviations with respect to the non-entangled hypothesis, this provides observation of quantum mechanical entanglement within t tbar pairs in this phase space. This measurement provides a new probe of quantum mechanics at the highest energies ever produced.
Observation of quantum entanglement in top quark pair production in proton–proton collisions at sqrt(s)=13 TeV
Tornago, M;Cappati, A;Amapane, N;Argiro, S;Bellan, R;Bellora, A;Costa, M;Covarelli, R;Grippo, M;Kiani, B;Luongo, F;Markovic, L;Mecca, A;Meridiani, P;Migliore, E;Mulargia, R;Obertino, MM;Pacher, L;Siviero, F;Sola, V;Solano, A;Tarricone, C;Umoret, G;Shchelina, K;Rumerio, P;Ravera, F;Salvatico, R;Vagnerini, A;
2024-01-01
Abstract
Entanglement is an intrinsic property of quantum mechanics and is predicted to be exhibited in the particles produced at the Large Hadron Collider. A measurement of the extent of entanglement in top quark-antiquark (t tbar) events produced in proton-proton collisions at a center-of-mass energy of 13 TeV is performed with the data recorded by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 36.3 fb−1. The events are selected based on the presence of two leptons with opposite charges and high transverse momentum. An entanglement-sensitive observable D is derived from the top quark spin-dependent parts of the t tbar production density matrix and measured in the region of the t tbar production threshold. Values of D < − 1 / 3 are evidence of entanglement and D is observed (expected) to be −0.480 −0.029 +0.026 (−0.467 −0.029 +0.026) at the parton level. With an observed significance of 5.1 standard deviations with respect to the non-entangled hypothesis, this provides observation of quantum mechanical entanglement within t tbar pairs in this phase space. This measurement provides a new probe of quantum mechanics at the highest energies ever produced.
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