Nobel Prize Honors Two Physicists for Symmetry Breaking Mechanism

This year's Nobel Prize for physics was awarded to François Englert of the Université Libre de Bruxelles and Peter Higgs of the University of Edinburgh, for developing the theory of what is commonly called the Higgs field and the Higgs boson. Their research provided the mechanism that is used in the Standard Model of particle physics to explain why elementary particles have mass, and to unify the weak and electromagnetic forces.

The Nobel Committee's citation reads, "For the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS Experiments at CERN's Large Hadron Collider."

Physicists have been working to isolate the elusive Higgs boson and confirm the underlying Higgs mechanism in the decades since it was first predicted in the 1960s. CERN announced the discovery of the particle at the Large Hadron Collider in Geneva, Switzerland on July 4th of last year. The Higgs boson was the last missing piece of the Standard Model that was awaiting discovery.

"This year's prize is about something very small that makes all the difference," said Staffan Normark, Permanent Secretary of the Royal Swedish Academy of Sciences.

The Higgs field triggers the symmetry breakdown that gives elementary particles their mass. The more strongly an elementary particle binds to the underlying field, the greater its mass. The Higgs boson is the particle associated with that field.

"The boson by itself is something that is the experimental test of the existence of the whole mechanism and one had to wait," Englert said. "It took some time to first prove the consistency of our theory…During the '70s the Standard Model was built up and only after that could one look for a test because the Standard Model was wonderfully verified, except for the missing element, which was that boson, whose condensation is what gives the mass to particles and short range forces."

To isolate the particle experimentally, scientists constructed the world's largest and most powerful particle accelerator near Geneva. The LHC's 17-mile ring runs under both Switzerland and France, and accelerates protons to collision energies of up to 7 TeV. Scientists painstakingly scrutinized the remains of the collisions for any telltale signs of a decayed Higgs. After two years of operation, and more than 300 trillion individual collisions, the LHC's two detector collaborations, ATLAS and CMS, jointly announced their discovery of the Higgs boson at last July's press conference.

"The discovery of the Higgs boson has captured the imagination of physicists and the public alike," said APS President Michael Turner. "It is hard to find a cab driver anywhere in the world who when he knows you are physicist doesn't ask about the Higgs boson. This is a tremendous achievement, involving more than 10,000 physicists from around the world to build, operate and analyze data from the most complex and most expensive science experiment ever built." 

The theory of what would ultimately be called the Higgs field was first proposed in three papers in Physical Review Letters, written by six people on three independent teams, all published in 1964. The researchers' theories explained the "broken symmetry" origin of particle masses, and also showed why photons, the particles that carry the electromagnetic force, have no mass while W and Z bosons, the purveyors of the weak nuclear force, can be massive. The Higgs mechanism effectively unified the weak and electromagnetic forces. These papers laid the groundwork for the later development of the Standard Model of particle physics.

Englert and his longtime collaborator, the late Robert Brout, also from the Université Libre de Bruxelles, authored the first of the 1964 papers. Higgs was the sole author of another, and the third was by Carl Hagen, now at the University of Rochester, Gerald Guralnik of Brown University, and Tom Kibble at Imperial College. All six were awarded APS's 2010 J.J. Sakurai Prize for Theoretical Particle Physics for their work. Five of the six traveled to snowbound Washington DC in February of 2010 to receive the Prize. Higgs was unable to attend, citing health concerns.

"It's unfortunate that the Nobel Prize is limited to only three recipients," said R. Sekhar Chivukula, the 2010 Chair of the APS Sakurai Prize Selection Committee, "because failing to recognize the work of Hagen, Guralnik, Kibble and Brout is a significant oversight. I'm glad that the APS could award a prestigious prize in a way that makes clear just how important they all were in establishing the foundations of contemporary particle physics."

After the awards were announced, Hagen said that the confirmation of the particle last July was the culmination of nearly 50 years of work.

"I am very happy to see the recognition of the Swedish Academy for this area of work and want to offer my congratulations to François Englert and Peter Higgs," Hagan said in a statement. "As my colleague Tom Kibble has said, it is no surprise that with the Nobel Prize unable to go to more than three people, the Academy felt unable to include my co-authors and me. But I am nonetheless very proud of the work we did, at how complete our explanation was, and how that has contributed to our understanding of how particles obtain mass."