On July 4, 2012, physicists at the Large Hadron Collider (LHC) beneath Geneva, Switzerland, the most powerful particle accelerator ever built, announced that they had detected one of the most elusive and eagerly sought prizes in all of science: the fundamental particle called the Higgs boson. The Higgs boson was a final predicted-but-missing piece in the Standard Model that physicists have used for decades to describe how the most fundamental forces and particles of nature relate to one another and give the universe its observed properties. The detection of the Higgs boson therefore validates that the Standard Model is correct, though ultimately still incomplete. See also: Higgs boson; Large Hadron Collider (LHC); Particle accelerator; Standard model

The existence of the Higgs boson was first hypothesized more than 40 years ago by several physicists, including P. W. Higgs, after whom it was named. It emerged from so-called gauge theories that attempted to unite electromagnetic force and the electroweak force (which relates to the radioactive stability of atomic nuclei). The gauge theory approach worked but it would only apply to particles without intrinsic mass. To explain how particles could therefore have mass, physicists postulated that mass arose from the particles’ interactions with a pervasive Higgs field. The Higgs boson emerged as a manifestation of that field. See also: Electroweak interaction; Fundamental interactions; Quarks

The Higgs boson neatly filled a vacancy in physicists’ new Standard Model. Testing whether it existed, however, proved to be difficult because theories suggested that signs of it could only be found in particle accelerators operating at energies that were vastly beyond anything that the particle accelerators of the 1970s could hope to match. Although physicists did conduct hopeful experiments with some powerful instruments in the late twentieth century, confirmation of the Higgs boson’s existence had to wait for the construction of the LHC by the European Laboratory for Particle Physics (CERN), which was not fully operational and online until 2011.

Two experiments at the LHC, called ALICE and ATLAS, independently made observations that contributed to the Higgs boson announcement. Technically, neither of these experiments proved the particle’s existence: Rather, they made credible, repeatable observations of particle decay that were highly consistent with certain expectations of what the Higgs boson would produce. They therefore either confirmed the existence of the Higgs boson or of something very much like it. See also: Higgs found; Tantalizing hints of long-sought particle

Now that those observations seem to have pinned down some of the properties of the Higgs boson more specifically, physicists can fold them into their theories in pursuit of an even more detailed understanding of how the universe works.