Sometimes a Higgs boson decays into two Z bosons, heavy particles that carry the weak nuclear force and exist for only a tiny fraction of a second. Researchers at CERN’s Large Hadron Collider studied how those two Z bosons spin, measured through the electrons or muons they turn into, and found the pattern you would expect if the pair is quantum entangled.
Both the ATLAS and CMS experiments looked at this, and CERN describes the result as “strong evidence,” not a final discovery. Entanglement has been tested many times with light and small particles. This is one of the first times it has been checked with such heavy particles at such extreme energies.
Why it matters: Entanglement is one of the strangest predictions of quantum mechanics, and it keeps holding up. Testing it in a totally new setting is a way of checking whether our current theory of particles still works there. If you want the basics first, start with our entanglement lesson.