ATLAS and CMS observed quantum entanglement in top-antitop quark pairs

2024-09-26 19:39:15

The Spanish physicist Juan Ramón Muñoz de Nova, together with Yoav Afik, a member of the ATLAS collaboration, proposed in 2020 a large-scale beamforming technique to observe coherence in the high-energy collisions of the LHC at CERN. In particular, in the lepton decays of pairs of top-antitop quarks a correlation will be observed in the angular separation of the leptons generated is the engagement between the spins of said quarks; As a note, the entanglement marker D is proposed, such that -1 The first successful nature of the said method, a value D = -0.547 ± 0.002 (stat.) ± 0.021 (syst.) = -0.547 ± 0.021, for mass in the center of mass of the upper-antitop pair between 340 and 380 GeV/c²; This result is more than ten sigma (standard deviations) from the -1/3 value, and was obtained after analyzing 140 fb⁻¹ of proton-proton collisions at 13 TeV cm in LHC Run 2. This result was announced in September. 2023 and has been confirmed by CMS collaboration in May 2024 (will appear in Reports on Progress in Physics) with an estimate of D = -0.480 ± 0.029, after examining 36.3 fb⁻¹ of collisions at 13 TeV cm, which is five sigma from the -1/3 value. In September 2024 (will appear in Physical review D) confirmed it with other concentrations at energies higher than 800 GeV/c² after analyzing 138 fb⁻¹ of LHC Run 2 collisions.

It has been considered using the top quark because its half-life (∼ 10⁻²⁵ seconds) is shorter than the hadronization rate (∼ 10⁻²⁵ seconds) and the spin rate (∼ 10⁻²¹ seconds). Thanks to this, the interaction between the spins of the top and antitop quarks turns into their decay products. To observe it clearly, we must apply to the lepton decays, through the electron, from the half-life of the W boson (~3).$$x$$10⁻²⁵ seconds) is also shorter than the rotational speed; essentially, we resort to decay t → Wb → b ℓ ν, in which the top decays to the bottom and the W boson, which decays to a lepton (electron or muon) and a neutrino (and the same for the antitop). Both ATLAS and CMS can detect the angle between the two leptons, either electrons or muons, with great accuracy, allowing the restriction symbol D to be computed as the product of two qubits, described by a 4×4 matrix, with 15 real values ​​(a Hermitian n × n matrix of trace unity in n² – 1). Determining all the denominators is very difficult, so we need a note; Muñoz de Nova and Afik proposed using D = tr(C)/3 = -(1 + δ)/3, with δ>0 for clutch (according to the Peres–Horodecki criterion). Its advantage is that the differential cross section for the angular separation between leptons is (1 – D cos φ) / 2, with φ the angle between the lepton directions. This parameter is not only possible, but the most obvious. In fact, CMS published in 2019 an analysis of these angles leading to D = -0.237 ± 0.011 > -1/3 for the entire mass of the antitop pair. For this reason, Muñoz de Nova and Afik proposed in 2020 that a lower mass should be analyzed, below 450 GeV/c² (and above twice the mass of the top quark).

The new ATLAS result and the new CMS results are amazing. Although everyone knows that there is always a entanglement between pairs of particles produced in LHC collisions, the observation is not easy. Thanks to the interpretation of good attention, this important event has been successful. The paper is the ATLAS Collaboration, “Observing quantum entanglement with top quarks in the ATLAS detector,” Nature 633:542-547 (18 September 2024), doi: https://doi.org/10.1038/s41586-024-07824-z, arXiv: 2311.07288 [hep-ex] (13 November 2023); CMS Collaboration, “Observation of quantum confinement in top quark pair production in proton-proton collisions at √s = 13 TeV,” Reports on Progress in Physics (submitted), arXiv:2406.03976 [hep-ex] (06 June 2024), doi: https://doi.org/10.48550/arXiv.2406.03976; y CMS Collaboration, “Measurements of polarization and spin reorientation and observation of entanglement in top quark pairs using lepton events + jets from proton-proton collisions at √s = 13 TeV,” Physical Review D (submitted), arXiv :2409.11067 [hep-ex] (September 17, 2024), doi: https://doi.org/10.48550/arXiv.2409.11067.

The scientific papers that proposed the original concept of the new technique are Yoav Afik, Juan Ramón Muñoz de Nova, “Entanglement and quantum tomography with top quarks at the LHC,” The European Physical Journal Plus 136: 907 (03 Sep 2021) , doi: https://doi.org/10.1140/epjp/s13360-021-01902-1, arXiv: 2003.02280 [quant-ph] (04 Mar 2020), and Yoav Afik, Juan Ramón Muñoz de Nova, «Quantum information with top quarks in QCD,» Quantum 6: 820 (29 September 2022), doi: https://doi.org/10.22331/q-2022-09-29-820, arXiv: 2203.05582 [quant-ph] (10 March 2022).

In quantum physics, when two particles have the same origin they will bind each other in some of their properties. In the particular case of a gluon of uniform spin that produces a top-antitop pair, both of spin 1/2, their spins result in a trapped state. Most of the LHC hadronic collisions are very noisy, due to collision stacking, which means that correlations between spins are lost (spin enhancement occurs). Therefore, observing the quantum nature in such collisions requires a very subtle analysis. Fortunately, the top quark decays so quickly that its products are marked by their spin reorientation; If these products also decay quickly into observable particles, as occurs in the lepton decay of the W boson, we can use the observed particles to observe the collision.

As the figure that opens this article shows, ATLAS has observed the affinity for antitop pairs with a central mass of 340 and 380 GeV/c², resulting in a value of D = -0.547 ± 0.002 (stat.) ± 0.021 (stat.) syst.) -1/3, and greater than 500 GeV/c² we get D = -0.098 ± 0.001 (stat.) ± 0.021 (syst.) > -1/3. According to the theoretical calculations of Muñoz de Nova and Afik, the correlation with the D parameter can be observed up to about 550 GeV/c². As this figure shows, there are other combinations of 15 correlation matrix parameters that can be used for large masses.

As always in particle physics, the observation at many sigmas (of ATLAS exceeds ten) should always be taken with caution (perhaps for this reason the article sent to Nature on November 14, 2023 was not received until July 12, 2024). ). Independent verification is often required. Fortunately, CMS published on arXiv on June 6, 2024 a special acknowledgment for the acceptance in Nature of the ATLAS article (signed by Muñoz de Nova, although not a member of the collaboration; a very impressive exercise in the field). CMS analyzed 36.3 fb⁻¹ of collisions by two methods, to obtain for the masses of the top-antitop pair between 345 and 400 GeV/c² a value of D = -0.480 ± 0.017 (calc.) ± 0.023 (syst. )

Since everyone likes records (like this year is Olympic), CMS published its analysis in September of all its LHC Run 2 collisions (138 fb⁻¹). He used various entanglement markers, such as and $Delta_E$, using collision with small angle |cos θ| Nature (perhaps by taking advantage of Muñoz de Nova), but CMS will publish a record of power Physical review D. Of course, ATLAS will follow the saga next year. This type of healthy competition always benefits the advancement of science.