Peter Higgs, from the University of Edinburgh, UK, and Francois Englert, from the Free University of Brussels, have been awarded the Nobel Prize in physics for 2013 for their work in understanding how elementary particles acquire mass. Higgs and Englert conducted their research independently but almost simultaneously in 1964; Englert worked with American physicist Robert Brout, who died in 2011 and therefore couldn’t be awarded the Prize.
Before Peter Higgs’s work, the Standard Model of particle physics, a framework of laws that describes the behaviour of fundamental particles, didn’t have an answer to the question of mass. Of course, the Model itself shaped up only in the 1970s, but Higgs’s work was important to understand what the Model would or wouldn’t accommodate. Together, Higgs and Englert described a mechanism, since called the Higgs mechanism, to explain the process of mass-‘formation’ as it could have happened a billionth of a second after the Big Bang 13.82 billion years ago. Today, their contribution is considered a cornerstone of modern particle physics.
The foundation of Higgs’s and Francois’s research lies in the work of Japanese physicist Yoichiro Nambu, who won the Nobel Prize for physics in 2008. Inspired by observations of superconducting materials from condensed-matter physics, Nambu had proposed a process called spontaneous symmetry breaking in the context of the strong nuclear interaction, one of the four fundamental forces of nature, to describe how relatively lighter particles like quarks can come together to form disproportionately heavier particles like protons and neutrons. However, Nambu’s theory lacked a relativistic model, which could have been used to explain what Higgs and Englert did at higher energies. His theory was also faulted because it wrongly predicted the existence of certain massless particles.
To unravel the Higgs mechanism: During the Big Bang, a sea of energy was unleashed into the universe by the explosion. It was probably symmetrical, which means one part of the ‘sea’ was indistinguishable from every other part across some time period. Just 10 seconds later, however, the symmetry was violated and broken because of some fluctuations in the field of energy, giving rise to new laws of physics.
In particle physics, this event is called spontaneous symmetry breaking. Higgs, Englert and Brout independently devised a mechanism through which this event and its repercussions could impart mass to some matter and force particles. Their theory relied on an invisible field of energy called the Higgs field pervading throughout the universe. This was supposed to be a quantum field, which meant that it had some average positive energy. When disturbed, waves would ride through the field like ripples on water. The smallest possible ripple, as with any field, is called a particle; such a particle of the Higgs field is called the Higgs boson.
When elementary particles move through the Higgs field, Higgs bosons couple to them to varying extents — stronger the coupling, more the retardation of the particle’s motion through the field, greater its mass. For this mechanism to have arisen the way it did after the Big Bang, four particles were deemed necessary. Three of them, the two W particles and the one Z particle (all bosons) were absorbed by the mediating electroweak forces — which comprise the electromagnetic and the weak forces, two of the four fundamental forces of nature.
This way, Higgs and Englert succeeded in providing a mathematical basis for how particles acquired mass in general, and how the W and Z bosons acquired mass specifically.
Afterward, physicists Tom Kibble (UK), Gerald Guralnik and Carl Hagen (both USA) published more results on the Higgs mechanism. In 1968, American theoretical physicist Steven Weinberg and Abdus Salam, a Pakistani, incorporated the Higgs mechanism into the then-fledgling Standard Model. In 1983, according to the Model’s predictions, the W and Z bosons were discovered at the UA1 and UA2 experiments at the European Organisation for Nuclear Research (CERN).
However, finding the Higgs boson itself was a more arduous journey. This particle was a smoking gun: finding it would mean the Higgs field also existed, and would conclusively validate Higgs’s and Englert’s research.
To take this step, the Large Hadron Collider (LHC) was planned by and built at CERN. Construction took from 1998 to 2008, involving more than 10,000 scientists and engineers from hundreds of universities, and over $9 billion.
Without a doubt, it is the most complex scientific experiment ever to be built, and its first purpose to find if a Higgs boson existed.
The LHC commenced planned research operations in March, 2010, involving over 3,000 personnel to operate it. On July 4, 2012, the ATLAS and CMS detector collaborations, which analysed the results produced at the LHC, announced that they had spotted the first hints of a Higgs-boson-like particle.
After more experiments and testing, in January 2013, CERN announced that the particle was indeed the Higgs boson. It turned, at that moment, that the mathematical framework developed by Peter Higgs and Francois Englert almost 50 years ago did describe an aspect of nature and was real.
While the LHC and the collaborating experimental physicists only received passing mention in the Nobel Prize citations of Higgs and Englert, they were the ones responsible for cementing the place of the Higgs mechanism in the Standard Model.
Now, physicists can move on to other problems that the Model still hasn’t solved, such as finding what dark matter is, why matter has been generated as some types of particles and not more or less, and why some forces of nature are so much stronger than others.
The LHC will reopen in 2015 with upgrades to boost its collision energy and luminosity, aspects instrumental in finding more elusive particles that could expose flaws in the Model and open the door for other, more encompassing, theories of physics to make their presence felt.
(Here is an interesting interview of Drs. Francois Englert and Robert Brout by A. Rangarajan, published in The Hindu in 2008.)