30 December 2013

Nobel prizewinners: Physics

By and Elizabeth Finkel
In the second part of our series on 2013 Nobel Prize winners, we assess the work of Peter Higgs and Francois Englert.

It’s been dubbed “the God particle” and “the Goddamn particle”. Now the Higgs boson has won the 2013 Nobel Prize in Physics for two of the researchers who independently proposed its existence in 1964: 80-year-old Belgian physicist François Englert and British physicist Peter Higgs, aged 84. Higgs proposed it first and the particle was given his name. Englert’s colleague, Robert Brout, died in 2011 and the prize is not awarded posthumously.

The prize was awarded in October after results from the Large Hadron Collider (LHC) at CERN, the European Organization for Nuclear Research in Switzerland, confirmed in March that a particle they had detected was, in all likelihood, the Higgs boson. While physicists worldwide celebrated, Higgs, who is almost as elusive as the particle, only discovered he’d won the prize when a woman congratulated him on the street in London.

There is a reason this long-sought particle has been revered and cussed. It is the missing keystone of the Standard Model, a theory describing the fundamental building blocks and forces of the universe. To test how well the model reflects reality, physicists look for the particles that it predicts in the wreckage created by particle colliders. The model has catalogued a table of elementary particles such as quarks, electrons and neutrinos. It explains how they interact with each other through particles known as bosons. Bosons are the force carriers. Photons, for instance, are bosons that carry the electromagnetic field.

The Standard Model has a superb track record. In the 1960s it predicted W and Z bosons that would transmit the so-called “weak” force (responsible for radioactive decay and fusion). In the 1980s, those bosons were found at CERN, now the home of the LHC.

The Higgs boson was also predicted in the 1960s. This profound boson was to be responsible for imparting mass. Without it our universe would be a blur of massless particles whizzing around at light speed. But for decades the Higgs boson remained stubbornly elusive.

There were fears a black hole would swallow Geneva

The US$10 billion LHC, dubbed the “genesis machine” was built to find it. It accelerates protons to 99% light speed on a 27 km collision course beneath the Swiss-French border. The forces released by such collisions have not been seen since the big bang. After 15 years of construction, it fired up in September 2008 amidst fears that it could create a mini black hole that would swallow Geneva. A needless concern: the machine blew a fuse and took until March 2010 to get running again. After several false sightings, in December 2011 a particle that lay in the expected mass range for a Higgs boson was registered by two independent detectors and their fiercely competitive teams at the LHC. According to the Atlas team, the new particle had a mass of 126 billion electron volts; according to the CMS team, it was 124 billion. But the shower of gamma rays that signalled the disintegration of a Higgs boson, could also be a chance artefact. To be certain, the physicists had to produce more data to give it odds of greater than one in a million of occurring by chance. On 4 July 2012 in CERN, and simulcast at the 36th International Conference on High Energy Physics in Melbourne, the announcement was made that the discovery of the Higgs was nigh. “This is a milestone for the physics community, and for human understanding of the fundamental laws that govern the universe,” effused Geoff Taylor, the director of Australia’s ARC Centre of Excellence for Particle Physics at the Terascale.

Confirmation came in March 2013. The press release from CERN was still cautious: “It remains an open question, however, whether this is the Higgs boson of the Standard Model of particle physics, or possibly the lightest of several bosons predicted in some theories that go beyond the Standard Model. Finding the answer to this question will take time.”

Nevertheless the March finding confirms the existence of the Higgs field which, like cosmic molasses, interacts with particles to give them mass. Scientists will now examine the LHC data to determine whether the properties of the Higgs can explain the mystery of gravity and more exotic phenomena such as dark matter or why there is more matter than antimatter in the universe.

As Caltech physicist Sean Carroll put it, “The Higgs discovery is the end of one era and the beginning of another.”

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