Physicists at CERN’s Large Hadron Collider have confirmed that quantum entanglement survives high-energy proton collisions by tracking Z boson pairs, while researchers separately announced the discovery of a new baryon, the Xi-cc-plus, marking major milestones for the world’s most powerful particle accelerator.
The Large Hadron Collider continues to push the boundaries of experimental physics, yielding two major discoveries inside the subterranean ring running along the Franco-Swiss border near Geneva, Switzerland. Operating deep beneath the surface, Europe’s CERN physics laboratory announced both the observation of quantum entanglement in extreme particle collisions and the identification of a rare new particle during recent runs of the accelerator.
Quantum Entanglement Survives Extreme Collider Conditions
Physicists from the ATLAS Collaboration at the Large Hadron Collider have confirmed that quantum entanglement—the phenomenon Albert Einstein famously described as spooky action at a distance
—can remain intact under the most extreme conditions ever produced in a laboratory.
Researchers analyzed data from proton-proton collisions occurring at thirteen trillion electron volts, generated by smashing together protons traveling at 99.99% the speed of light. While quantum entanglement underpins emerging technologies like quantum computers and ultra-secure communication networks, whether the delicate phenomenon could survive the short-lived, highly energetic collisions inside a particle smasher remained an open question.
Using the ATLAS detector, physicists found strong evidence of entanglement between pairs of Z bosons produced when a Higgs boson decays. Because Z bosons vanish almost instantly, the research team tracked the electrons and muons left behind to reconstruct the angles at which those particles flew apart.
The findings, published in the journal Physical Review Letters, rank among the highest-energy confirmations of entanglement ever recorded. University of Oxford’s Professor Alan Barr noted that entanglement forms the heart of quantum information science and quantum field theory. Professor Chris Timpson called the collider experiments detecting entanglement a new frontier in investigations of the foundations of quantum mechanics,
while Professor Daniela Bortoletto emphasized that the measurement demonstrates the unique capabilities of the Large Hadron Collider.
The Discovery of the Xi-cc-plus Baryon
Similar to a proton but roughly four times heavier, the newly found particle contains two charm quarks and one down quark, whereas normal protons consist of two up quarks and one down quark.
Vincenzo Vagnoni, spokesman for the Large Hadron Collider beauty (LHCb) experiment, noted it was only the second time a baryon with two heavy quarks had been observed. It is also the first new particle identified following upgrades to the LHCb detector completed in 2023. The collaboration observed the baryon by analyzing proton-proton collision data from the third run of the LHC, reaching a statistical significance of 7 sigma—well above the 5 sigma threshold required to claim a discovery.
Because of complex quantum effects, the new particle features a predicted lifetime up to six times shorter than its 2017 counterpart, which featured an up quark instead of a down quark. CERN Director-General Mark Thomson called the finding a fantastic example of how LHCb’s unique capabilities drive the accelerator’s ongoing success.
Inside the 27-Kilometer Subterranean Ring
Both discoveries rely on the specialized engineering of the Large Hadron Collider, which sits in a 27-kilometer ring running 100 meters underground near Geneva, Switzerland. Originally starting up on September 10, 2008, the facility uses thousands of superconducting electromagnets chilled with liquid helium to ‑271.3°C—a temperature colder than outer space—allowing electricity to flow without resistance.
All operations and technical infrastructure are managed from the CERN Control Centre, where beams are guided to collide at four locations housing massive detectors like ATLAS and LHCb. As researchers continue to probe the foundations of quantum mechanics and test theories of the strong force, CERN is already planning an even larger particle smasher, the Future Circular Collider, to continue probing the mysteries of the universe.