Quantum Entanglement between “Top Quarks” at the Highest Energies Observed  

The researchers at CERN have succeeded in observing quantum entanglement between “top quarks” and at the highest energies. This was first reported in September 2023 and since confirmed by a first and second observation. The pairs of “top quarks” produced at the Large Hadron Collider (LHC) were used as a new system to study entanglement. 

The “top quarks” are the heaviest fundamental particles. They quickly decay transferring its spin to its decay particles. The top quark’s spin orientation is inferred from the observation of decay products.  

The research team observed quantum entanglement between a “top quark” and its antimatter counterpart at an energy of 13 teraelectronvolts (1 TeV=10¹²  eV). This is the first observation of entanglement in a pair of quarks (top quark and antitop quark) and the highest-energy observation of entanglement so far. 

Quantum entanglement at high energies has remained largely unexplored. This development paves the way for new studies.  

In quantum entangled particles, the state of one particle is dependent on others irrespective of distance and the medium separating them. The quantum state of one particle cannot be described independently of the state of the others in the group of entangled particles. Any change in one, influences others. For example, an electron and positron pair originating from decay of a pi meson are entangled. Their spins must add up to the spin of the pi meson hence by knowing spin of one particle, we know about the spin of the other particle.  

In 2022, the Nobel Prize in Physics was awarded to Alain Aspect, John F. Clauser and Anton Zeilinger for experiments with entangled photons. 

Quantum entanglement has been observed in a wide variety of systems. It has found applications in cryptography, metrology, quantum information and quantum computation. 

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References:  

1. CERN. Press release – LHC experiments at CERN observe quantum entanglement at the highest energy yet. Published 18 September 2024. Available at https://home.cern/news/press-release/physics/lhc-experiments-cern-observe-quantum-entanglement-highest-energy-yet  

2. The ATLAS Collaboration. Observation of quantum entanglement with top quarks at the ATLAS detector. Nature 633, 542–547 (2024). https://doi.org/10.1038/s41586-024-07824-z 

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FUNDAMENTAL PARTICLES  – A Quick look

Fundamental particles are classified into Fermions and Bosons based on spin.

[A]. FERMIONS have spin in odd half integer values (½, 3/2, 5/2, ….). These are matter particles comprising of all quarks and leptons.   – follow Fermi–Dirac statistics,   – have a half-odd-integer spin   – obey the Pauli exclusion principle, i.,e, two identical fermions cannot occupy the same quantum state or the same location in space with the same quantum number. They cannot both spin in the same direction, but they can spin in opposite direction   The fermions include all quarks and leptons, and all composite particles made of an odd number of these.  – Quarks = six quarks (up, down, strange, charm, bottom and top quarks).  – Combine to form hadrons such as protons and neutrons. – Can not be observed outside of hadrons.   – Leptons = electrons + muons + tau + neutrino + muon neutrino + tau neutrino.    – ‘Electrons’, ‘up quarks’ and ‘down quarks’ the three most fundamental constituents of everything in the universe.   – Protons and neutrons are not fundamental but are made up of ‘up quarks’ and ‘down quarks’ hence are composite particles. Protons and neutrons are each made of three quarks – a proton consists of two “up” quarks and one “down” quark whereas a neutron contains two” down” and one “up.”  “Up” and “down” are two “Flavors,” or varieties, of quarks.  – Baryons are composite fermions made of three quarks, e.g., protons and neutrons are baryons  – Hadrons are composed of quarks only, e.g., baryons are hadrons.

[B]. BOSONS have spin in integer values (0, 1, 2, 3, ….)   – Bosons follow Bose-Einstein statistics; have integer spin.   – named after Satyendra Nath Bose (1894–1974), who, along with Einstein, developed the main ideas behind the statistical thermodynamics of a boson gas.   – do not obey the Pauli exclusion principle, i.,e, two identical bosons can occupy the same quantum state or the same location in space with the same quantum number. They can both spin in the same direction,   – Elementary bosons are the photon, the gluon, the Z boson, W boson and the Higgs boson. Higgs boson has spin=0 while the gauge bosons (i.e., photon, the gluon, the Z boson, and W boson) have spin=1.   – Composite particles can be bosons or fermions depending on their constituents.  – All composite particles made up of an even number of fermions is a boson (because bosons have integer spin and fermions have odd half-integer spin).   – All mesons are bosons (because all mesons are made of an equal number of quarks and antiquarks). Stable nuclei with even mass numbers are bosons e.g., deuterium, helium-4, Carbon -12 etc.  – The composite bosons also do not obey Pauli exclusion principle.   – Several bosons in the same quantum state coalesce to form “Bose-Einstein Condensate (BEC).”

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