Discovery of Higgs boson and its implications

Prof N. Nimai Singh *

The decay of the Higgs boson to a pair of photons - dashed yellow lines and green towers :: Pix - CERN

The claim for discovery:

On 4 July 2012, at a seminar held at CERN, Geneva where LHC experiment is going on, ATLAS spokesperson Fabiola Gianotti and CMS spokesperson Joe Incandela jointly presented their preliminary results, claiming the discovery of a new particle consistent with long-sought Higgs boson of the Standard model, in the mass region around 125-126 GeV at the level of 5 sigma standard deviation needed for a discovery.

According to CERN Research Director Serglo Bertolucci, the observation of this new Higgs-like particle indicates the path for the future towards a more detailed understanding of what they are seeing provides the experiments with more data. CERN Director General Rolf Heur while announcing the discovery, remarked that such discovery of a particle consistent with the Higgs boson opens the way to more detailed studies, requiring larger statistics, which will pin down the new particle's properties, and is likely to shed light on other mysteries of our universe.

This event is considered to be the biggest thing to happen in fundamental physics in about 30 years since the discovery of the W and Z vector bosons at CERN. It is indeed a huge success for high energy physics, vindicating at the same time the colossal efforts that have gone into making the LHC and its detectors work, as well as the theoretical framework of the electroweak part of the Standard Model.

It can be mentioned that just five days before the historic CERN's claim for discovery, the US based Tevatron experiments at FermiLab presented their update on Higgs search and their signals are not strong enough to claim evidence for new state, and don't match the significance of the CMS and ATLAS results.

This implies that there is still room for debate that the discovered new resonance at CERN, is indeed the Higgs boson that induces the electroweak symmetry breaking and gives masses to both SM vector bosons and to fermions. Higgs decay to Gamma-gamma is the interesting channel to watch, it is about 2 sigma high above the SM prediction. Similarly the Tevatron bb result is also a bit high.

Higgs evidence: This shows a collision with characteristics consistent with the existence of the God particle :: Pix - CERN

The Higgs fields:

In 1964 Peter Higgs of the University of Edinburgh, U.K., proposed that some sort of scalar field fills the entire physical vacuum as pervasive medium. A scalar field popularly known as the Higgs field under its originator, was introduced to satisfy the condition of spontaneous symmetry breaking of the local gauge symmetry whereby the gauge bosons get masses.

A scalar field is a field which has the same properties viewed from every direction and is indistinguishable from empty space in the sense that its additive quantum numbers are zero such as spin-zero, charge-zero etc. There are certain unusual properties of the Higgs field. It costs less energy to have it than not to have it. Higgs field can be present even in the vacuum, without any particle, or other force fields. It is an environment through which all elementary particles swim.

A particle's interaction with the value of Higgs field in the vacuum known as Higgs condensate, could slow it down by imparting mass on it. Higgs condensate which fills the physical vacuum, will happen only when vacuum state with the condensate is more stable than without. This means the condensate has lower energy from ordinary vacuum having no condensate. This implies the condensate has a negative energy density which exerts a positive pressure on its surrounding.

The ability to form a condensate in vacuum depends on a number of factors including the ambient temperature of the surroundings. The Higgs field is hypothesized to have the ability to form Higgs condensate under special condition and this induces the so-called spontaneous symmetry breaking mechanism. By definition the vacuum is the state with lowest possible energy, with quantum fluctuations within it, which allow virtual particles to be continuously created and annihilated forming a constant mist in vacuum.

This mist of virtual particles comes and goes constantly. However, if a strong attraction exits among them, they might stick together, in the process releasing enough of the borrowed energy to enable them a permanent existence. This is how a vacuum condensate is formed.

Higgs mechanism:

Originally a gauge boson was massless because it has no third spin orientation. To make it massive, the missing longitudinal degree of freedom should be supplied, and this is exactly the role of the Higgs field if it is properly coupled to the gauge field.

In other words, the presence of Higgs condensates in vacuum slows down the massless gauge bosons travelling in vacuum through their interaction, thus making the gauge bosons massive. When particles of matter such as electrons or quarks travel through the Higgs field, they are constantly flipped "head-over-heels".

This forces them to move more slowly than their natural speed, that of light, by making them heavy. If there is no Higgs field, symmetry is perfect and all particles are indistinguishable. Thus Higgs field indirectly gives structure to our world and makes it an interesting place. Like any other field in quantum-mechanical theory, the new Higgs field would have an energy and momentum that comes in bundles, known as quanta.

Electroweak theory tells us that at least one of these quanta should be observable as a new elementary particle known as Higgs particle or Higgs boson. Higgs bosons are the visible manifestations of the breaking of the electroweak symmetry. The central problem of particle physics today is to understand the origin of the breaking of the electroweak symmetry, the Higgs mechanism, the physical origin of the Higgs potential where imaginary mass to Higgs field is assigned.

A brief story on Higgs mechanism:

In 1962, Goldstone's theorem had shown that spontaneous breaking of symmetry in a relativistic field theory results in massless spin-zero bosons, which are excluded experimentally. In a paper published in the famous journal, Physical Letters on 15 September 1964, Peter Higgs showed that Goldstone bosons need not occur when a local symmetry is spontaneously broken in a relativistic theory. Instead, the Goldstone mode (massless scalar particle) provides the third polarization of a massive vector field. The other mode of the original scalar doublet remains as a massive spin-zero particle – the Higgs boson.

Higgs wrote a second short paper describing what came to be called "the Higgs model" and published it in Physical Review Letters. Higgs drew attention to the possibility of a massive spin-zero boson in the paper. The Higgs mechanism was applied to the electroweak theory independently by Steven Weinberg and Abdus Salam during 1970 in order to unify electromagnetic and weak interactions of elementary particles.

This unification involves a close relationship between the massless photon, which carries the long-range electromagnetic force, and the massive W and Z vector bosons, which carry the short-range weak force. The theory also predicts one Higgs boson and the search for the Higgs boson has become a major objective of experimental particle physics. Higgs' work has been a crucial step towards a unified theory of the forces of Nature.