Higgs boson

The Higgs boson is a massive spin-0 elementary particle in the Standard Model of particle physics that plays a key role in explaining the mass of other elementary particles. The experimental discovery of a particle consistent with the Higgs was announced in a seminar on July 4, 2012. This particle was first proposed by Professor Peter Higgs of Edinburgh University in 1964 as a means to explain the origin of the masses of the elementary particles by the introduction of an fundamental scalar field. This gives all the fundamental particles mass via a process of spontaneous symmetry breaking called the Higgs Mechanism. The Higgs boson was popularised as the "God particle" by the Nobel Prize-winning physicist Leon M. Lederman in his 1993 popular science book The God Particle: If the Universe Is the Answer, What is the Question? co-written with science writer Dick Teresi.

The Higgs mechanism

In the Standard Model, the theory that explains experimental observations of elementary particles, the QCD vacuum has less symmetry than the force laws governing fundamental interactions. This reduced symmetry situation is not unique, and is found in many systems, among them the ground state of ferroelectrics and of superconductors. In these systems, the greater symmetry of nature is exhibited "on average" by a mosaic of sub-domains individually with reduced symmetry, but statistically exhibiting the greater symmetry of the interactions when all the domains are viewed as an ensemble.

In the case of superconductors, the photons, whose exchange mediates the electromagnetic interactions between Cooper pairs, cannot propagate freely because of the presence everywhere of electric charge. In a similar fashion, the Higgs mechanism predicts the symmetry of electroweak interactions is broken by interactions among Higgs bosons in the vacuum, leading (among other things) to non-zero masses for the W^± and Z weak bosons. In fact, the properties of mass and electric charge stem from interaction with the reduced symmetry vacuum, and are not a result of direct interactions between particles.

Search for the Higgs boson

Studies using the Fermilab's Tevatron collider suggest a range for the mass of the Higgs boson between 115-150 GeV (gigaelectronvolts), assuming the correctness of the Standard Model of particle physics. See review of the experiments: The observed mass was placed at 125.3±0.6 GeV.

The Higgs particle was not made in the Tevatron collider, but by using the high energies of the Large Hadron Collider in Geneva. This discovery was an early goal of this major international project. The magnitude of this effort is huge:

"The data presented yesterday are the latest from the $10.5 billion Large Hadron Collider, a 27-kilometer (17-mile) circumference particle accelerator buried on the border of France and Switzerland. CERN has 10,000 scientists working on the project..."

The discovery was a bit anticlimactic, as theory has incorporated the Higgs boson for decades. As said by Stephen Hawking:

“This is an important result and should earn Peter Higgs the Nobel Prize” the physicist predicted. “But it is a pity in a way, because the great advances in physics have come from experiments that gave results we didn’t expect.”

Further experiments will explore the complete mechanism.