Eight months ago, physicists working with the world’s biggest atom smasher—Europe’s Large Hadron Collider (LHC)—created a sensation when they reported that they had discovered a particle that appeared to be the long-sought Higgs boson, the last missing piece in their standard model of particles and forces. Today, those researchers reported that the particle does indeed have the basic predicted properties of the standard model Higgs boson, clinching the identification.
“It sure does look like the standard model Higgs boson, you bet,” says Sally Dawson, a theorist at Brookhaven National Laboratory in Upton, New York, who was not involved with the measurements.
It’s a big step, at least semantically. Ever since the new particle was reported last July, officials at the home of the LHC—the European particle physics laboratory, CERN, near Geneva, Switzerland—have taken great care to describe the new thing as a “Higgs-like particle.” Now, a CERN press release calls the particle “a Higgs boson.” “That’s a big deal for the community,” Dawson says.
To make the positive identification, researchers relied not on dental records, but on observations of how the Higgs boson decays into combinations of other, more familiar particles. Key characteristics of the Higgs include its spin and its parity, a symmetry property. They can be determined by looking at correlations in the particle directions when, for example, a Higgs boson decays into two particles called Z bosons, each of which then decays into two particles called muons…