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

The Higgs Mechanism is vital in explaining the masses of the electroweak W and Z bosons. To understand the problem in giving mass to the vector bosons let us first consider the QED sector of the Standard Model Lagrangian.

${\mathcal {L}}_{QED}={\overline {\psi }}(i\gamma ^{\mu }\partial _{\mu }-m)\psi -j_{em}^{\mu }A_{\mu }-{\frac {1}{4}}F_{\mu \nu }F^{\mu \nu }$

Now consider how things will change if we perform a local phase rotation such that:

$\psi (x)\rightarrow \psi '(x)=e^{i\alpha (x)}\psi (x)$

We would expect the Langrangian to remain invariant under such a rotation since to do otherwise would mean that if I chose a different phase than someone else where we could get different physics results.

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 Higgs particle was not made in the Tevatron collider, but by using the high energies of the Large Hadron Collider in Geneva. The mass was placed at 125.3±0.6 GeV. This discovery was an early goal of this major international 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.