Plate Nº 35 · recorded October 10, 2026
PhysicsReported finding
ATLAS and CMS Find Strong Evidence for Z Boson Entanglement at the LHC
ATLAS and CMS at CERN have independently found strong evidence of quantum entanglement between pairs of Z bosons produced at the LHC, the highest-energy test of the strange quantum link yet.
By Marcus Bennett3 min read587 words
In brief
- Both ATLAS and CMS reported strong evidence of quantum entanglement between Z bosons on 17 September 2026.
- Z bosons can hold one of three spin values (−1, 0, +1); the two from a Higgs decay must carry opposite spins summing to zero.
- The analyses combined data from the LHC's second and third runs.
- In 2024, the same two collaborations first observed entanglement between top quarks, the heaviest fundamental particles known.
- The planned HiLumi LHC upgrade is expected to sharply increase collision counts and could turn the evidence into a definitive result.
The ATLAS and CMS Collaborations at CERN have independently found strong evidence of quantum entanglement between pairs of Z bosons at the Large Hadron Collider (LHC), reporting their results on 17 September 2026.
What is quantum entanglement?
Entanglement links two particles so that measuring one instantly fixes a property of the other, no matter the distance between them. Einstein and his colleagues argued that hidden properties must exist to determine the states of quantum systems before measurement, challenging quantum mechanics itself. Experiments over many decades have shown otherwise.
Photons, electrons, atoms, and small molecules have all been entangled in laboratories. The new ATLAS and CMS result adds Z bosons to that growing catalogue and shows the strange effect also emerges in a particle that carries a fundamental force. Studying it may help physicists explore how the Higgs boson interacts with the force-carrying particles of the Standard Model, the theory that catalogues all known particles and three of the four fundamental forces.
Why does it matter at high energies?
Most demonstrations of entanglement involve low-energy particles. The LHC smashes protons together at energies far higher than any tabletop experiment can reach, creating short-lived particles that decay almost immediately.
In 2024, the same two collaborations reported the first observation of entanglement between top quarks, the heaviest fundamental particles known. The Z boson result extends that high-energy program to a different particle.
Z bosons are different beasts. They carry the weak nuclear force, one of nature's four fundamental forces, and they vanish almost as soon as they appear.
Confirming the effect in such a fleeting particle is a technical feat. Future studies of entangled Z bosons could give physicists a new way to probe how the Higgs boson interacts with the particles around it, particularly at energies where the Standard Model has not been precisely tested.
How did the teams find it?
A Z boson can hold one of three spin values, which physicists label −1, 0, or +1. Spin is a quantum property tied to angular momentum.
The Higgs boson has spin 0, so the two Z bosons from a single Higgs decay must carry opposite spins. If one Z boson shows +1, the other must show −1. That mirror relationship is the signature of entanglement the teams searched for.
Z bosons decay almost immediately into pairs of:
- Electrons
- Muons, which are heavier cousins of electrons
Both ATLAS and CMS can spot those charged leptons and measure the angles at which they fly apart. Statistical analysis of those angles reconstructs the Z bosons' spin correlations and tests whether they cross the threshold for an entangled state. Both teams reported strong evidence that they do.
The signature is subtle, so the teams combined many collision events. Data from the LHC's second and third runs gave them enough statistics to see the effect.
What does this open up?
The Higgs boson is now a confirmed source of entangled particles at the highest energies yet probed. Entangled Z bosons may also offer a new way to study how the Higgs boson interacts with other particles at extreme energies. The Higgs boson's interactions remain one of the least-tested corners of the Standard Model, and any new probe is valuable.
What's next?
The collaborations describe the result as strong evidence rather than a confirmed observation. The planned HiLumi LHC upgrade will sharply increase collision counts. That boost could turn today's strong evidence into a definitive result and extend entanglement studies to rarer particle decays.
via journals.aps.org (Original)
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