Another chapter has unfolded in the dramatic saga of the Higgs boson. On the morning of October 8, 2013, the Swedish Academy of Science made an announcement that had been widely anticipated by the blogosphere: Francois Englert and Peter Higgs shared the 2013 Nobel Prize for physics for the prediction of a new physics mechanism to which Higgs (unwillingly) lent his name.
The Standard Model of particle physics is a stunningly successful theory that describes the matter of the universe. It was developed in the 1960s and has been extensively validated in the intervening decades. However, the theory had one striking weakness. It did not explain why the smallest and most fundamental particles had mass, instead of being massless, which seemed to be a more natural state of affairs.
In 1964, Belgian physicists Robert Brout and Francois Englert published a paper describing a way to modify a class of so-called Yang-Mills theories. By adding a new field of energy to the existing theories, they found, they could give subatomic particles mass.
British physicist Peter Higgs independently developed the idea and his treatment was published a couple of weeks later. A third treatment of the problem by the American physicists Gerald Guralnik, Carl Hagen, and Tom Kibble appeared shortly thereafter. All three papers were named Milestone Papers by the American Physical Society in its 50th anniversary issue. A fourth paper, written by Peter Higgs, made the crucial observation that if this modification was true, it predicted a new particle. Over the intervening years, the energy field has come to be called the Higgs field and the predicted particle the Higgs boson.
While the ideas described in these papers from 1964 were possible explanations for the origins of the mass of fundamental particles, the ideas could have been wrong. In order to test the theory, scientists began a search for the Higgs boson.
On July 4, 2012, after nearly 50 years of searching, researchers using the Large Hadron Collider (LHC) at the CERN laboratory in Europe announced that they had found a new particle that was “consistent with being” a Higgs boson. In science, the term “consistent with being” has a technical meaning. It means that some of the predicted properties had been tested and verified but not all. It also means that no observations disagreed with the theory. By way of an analogy, if scientists had discovered a fruit that was consistent with being an apple, they might have touched and looked at the fruit and confirmed that it was apple-like, but they had not smelled or tasted it yet. Because of these residual uncertainties, awarding a Nobel Prize for the successful prediction of the Higgs boson in 2012 would have been premature.
In March of 2013, researchers updated their results, using two and a half times as much data as they used in July of 2012. With the extra data and more refined analysis techniques, the scientists were able to confirm that the newly-discovered particles had even more properties that were identical to those the Higgs boson was predicted to have. The case supporting the Higgs discovery was firming up.
There remains some possibility that the newly-discovered-particle is not the Higgs boson. For instance, the theories of 1964 predicted that a single variety of Higgs boson exists. Given that scientists have found only one variety, this is great news for the prediction. However it could be that there are other varieties of Higgs bosons that have not yet been discovered. Being absolutely sure will require more data taken at the LHC when it resumes operations in 2015.
So why award the Nobel Prize before this additional confirmation? First, the observed particle has many properties that are identical to the predictions of 1964. Those predictions seem to be part of the story. Second, time is a real concern. The prize cannot be awarded posthumously, and both Higgs and Englert are in their 80s. (Brout died in 2011.)
Thanks to the near-synchronicity of the milestone Higgs papers, narrowing the field of Nobel candidates must have been difficult. While the details of the selection process are private, it appears that the Swedish Academy of Science acknowledged that Englert and Brout got there first, while Higgs was the first to associate the new field with a particle. The decision was no doubt a difficult one, but is consistent with how the prize has been awarded in the past.
Our ongoing study of the rules that govern the universe is not complete with the observation of the Higgs boson, but the discovery is a tremendous step forward. The 2013 physics Nobel Prize is an affirmation of the importance of those ideas, first conceived of nearly half a century ago.
Author’s suggestions for further reading
The Quantum Frontier: The Large Hadron Collider
Author Don Lincoln’s look inside the LHC and the physics it explores.
Massive: the Missing Particle that Sparked the Greatest Hunt in Science
Science writer Ian Sample’s examination of the quest for the Higgs.
Higgs: The Invention and Discovery of the God Particle
Science writer Jim Baggott on the history and implications of the Higgs discovery.
The Particle at the End of the Universe
Physicist Sean Carroll goes behind the scenes at the LHC to explore the story of the search for the Higgs.