http://cdsweb.cern.ch/journal/CERNBulletin/2012/28/News Articles/1459456?ln=en
Frequently Asked Questions: The Higgs!
Why have we tried so hard to find the Higgs particle? How does the Higgs mechanism work? What is the difference in physics between strong evidence and a discovery? Why do physicists speak in terms of "sigmas"? Find out here!
Why have we tried so hard to find the Higgs particle?
Because it could be the answer to the question: how does Nature decide whether or not to assign mass to particles?
All the fundamental particles making up matter – the electron, the quarks, etc. – have masses. Moreover, quantum physics requires that forces are also carried by particles. The W and Z particles that carry the weak force responsible for radioactivity must also have masses, whereas the photon, the carrier of the electromagnetic force, has no mass at all. This is the root of the “Higgs problemâ€: how to give masses to the fundamental particles and break the symmetry between the massive W and Z and the massless photon? Just assigning masses by hand leads to an inconsistent theory and nonsensical predictions. Nature must therefore have a way of correcting this inconsistency, and the mechanism proposed by Englert, Brout and Higgs could be the answer.
How does the Higgs mechanism work?
According to the Englert-Brout-Higgs mechanism, the property that we measure as the ‘mass’ of a particle is the result of a constant interaction with a field that permeates the Universe like a sort of “etherâ€. The existence of this Englert-Brout-Higgs field is definitively proven by the discovery of the corresponding quantum particle - the Higgs boson.
Originally, the Englert-Brout-Higgs mechanism was put forward to explain why one of Nature’s fundamental forces has a very short range, whereas another similar force has an infinite range. The forces in question are the electromagnetic force (infinite range) – which carries light to us from the stars, drives electricity around our homes, and holds together the atoms and molecules from which we are all made – and the weak force (very short range), which is responsible for radioactivity and drives the energy-generating processes of the stars. Today we know that the electromagnetic force is carried by particles called photons, which have no mass, whereas the weak force is carried by particles called W and Z, which do have mass. Rather like people passing a ball, interacting particles exchange these force carriers. The heavier the ball, the shorter the distance it can be thrown – and the heavier the force carrier, the shorter its range. The W and Z particles were discovered in a Nobel prize winning enterprise at CERN in the 1980s, but the mechanism that gives rise to their mass had not yet been understood, and that’s where the Higgs boson comes in.
The Englert-Brout-Higgs mechanism in its basic form is the simplest theoretical model that could account for the mass difference between photons and the W and Z particles, and by extension could account for the masses of other fundamental particles. The presence of the Englert-Brout-Higgs field enables these forces to cohabit a single unified electroweak theory.
It should not be thought that the Englert-Brout-Higgs field is responsible for all the mass in the Universe. Your interaction with the field actually contributes less than 1 kg to your mass. The remainder comes mainly from the strong force binding quarks inside nucleons, with a tiny contribution from the electromagnetic force that reigns over the atomic and molecular scales.
Higgs bosons are quantum fluctuations in the Englert-Brout-Higgs field that are visible experimentally only when energy is “injected†into the field. Concentrating the right amount of energy in proton-proton collisions at the LHC excites the Englert-Brout-Higgs field, which resonates at a precise energy corresponding to the mass of the Higgs boson. The Higgs boson appears momentarily before decaying into other particles that the LHC experiments can measure. Some theories predict the existence of multiple Higgs bosons.
Is the Higgs boson the only possible answer to the “mass problem�
No, there are other theories that predict the existence of different mechanisms to explain how Nature deals with the mass problem. For example, there are rival theories that suggest the existence of extra dimensions of space.
Also, despite the fact that we see strong evidence of its existence, we do not yet know whether the Higgs boson is an elementary particle as postulated in the Standard Model, or some more complex object. Nor do we know whether there is only one Higgs boson or if there are more of them. Further studies and analysis will have to be carried out to reply to these questions.
What is the impact of such a Higgs boson on the current description we use for the Universe?
The Higgs boson will complete our description of the visible matter in the Universe, and of the fundamental processes governing the Big Bang since it was a trillionth of a second old. The Higgs boson may have played a role in generating the matter in the Universe, and may be linked to dark matter. It may even provide a clue how the Universe inflated to its present size. On the other hand, the Higgs boson is a very different particle from the others we know, and poses almost as many questions as it answers. For example, what determines the mass of the Higgs boson and the density of dark energy? According to conventional ideas, both should be much larger than their observed values. The quest continues.