Scientists at CERN, the European Organization for Nuclear Research, said its researchers observed a particle that may be the Higgs boson, a theoretical particle that could explain where mass comes from.
The announcement coincides with the 36th International Conference on High Energy Physics in Melbourne. Here are answers to frequently asked questions about the Higgs boson. The information is drawn from the Science Media Centre of Canada and interviews and press briefings by physicists.
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Q: What is it?
The Higgs boson is a hypothesized elementary particle that, if confirmed, would provide the mechanism by which the other elementary particles in the universe have mass. Elementary particles are the smallest fundamental units of matter. It was once thought atoms were the smallest. Then there was the discovery of the atomic nucleus and its composition of two types of subatomic particles: protons and neutrons. Protons and neutrons are themselves made of elementary particles called quarks.
This discovery led to understanding that all matter is made up of quarks and electrons. Discoveries over the last 80 years have shown that electrons are a member of a class of other elementary particles called leptons. Elementary particles can be divided into two classes -- fermions and bosons -- which are defined by a quantum mechanical property known as "spin."
Scientists believe that, at a quantum level, the forces that cause quarks and leptons to attract or repel each other are carried by bosons.
The Standard Model of elementary particle physics is a theory that explains how quarks and leptons interact in terms of three forces: The electromagnetic force, strong nuclear force, and weak nuclear force.
The Higgs boson is notable in that its interactions with the other particles are thought to give these particles their mass, a fundamental constituent of our universe. The Higgs boson is also notorious as the only particle in the Standard Model that hasn't been directly observed.
Q: What does it do?
Scientists have theorized that the Higgs boson gives each type of particle its own mass. Its existence is needed to explain a number of the features of the Standard Model as it provides us with an understanding of why some particles have very large masses while others are quite light.
Physicist Peter Higgs proposed what we now call the Higgs field, and hypothesized that it spreads through the universe. All particles would acquire mass by interacting with this field. As is the case with the other interactions, at a quantum level this Higgs interaction predicts that we should be able to produce and detect the boson associated with it, or the Higgs boson.
Mass of the particles would be the result of interaction with the Higgs field, and this interaction produces a Higgs boson. Because the boson is predicted by the field, finding the Higgs boson would be evidence that the Higgs field exists.
Q: Why is the Higgs boson important?
The Standard Model has been stood up to scientific challenge. The Higgs is the last missing component, leaving open the question about the theoretic formulation given to the masses ascribed to all of the particles in nature.
If the Higgs boson is found, then the Standard Model will be further validated. If the Higgs boson is not found, then original problems with the Standard Model would need other explanations. There are other theories besides the Higgs boson that would help explain these inconsistencies. However, it may also indicate the model has fundamental flaws.
The research relates to fundamental physics, which has shaped basic scientific understanding and led to technologies from wireless Internet communications and World Wide Web to medical imaging and cancer radiotherapy.
The Higgs provides a theory on the origin of mass, which is why it's sometimes referred to as the "God particle."
Q: How do you find it?
Most elementary particles are found by colliding together pairs of elementary particles, bringing together large amounts of energy that can result in the creation of other particles.
To do this, particles must be accelerated toward each other at high speeds in an accelerator, and the results of the collisions must be observed by large detectors surrounding the collision point. Data from the detectors must then be analyzed. The Large Hadron Collider at the CERN laboratory in Geneva has been built over the last two decades to create these collisions.
The LHC collides protons together at the very highest energy achieved in a laboratory, 7 tera-electron Volts. Very occasionally, a Higgs boson would be produced in these collisions. However, there are many other collisions that are very similar to those that produce Higgs bosons but are not. They are considered as "background" events, and they have to be quantified. When one sees a significant excess of "Higgs- like" events above the expected backgrounds can one claim evidence for the existence of a Higgs boson.
Q: Who's looking?
Only a few accelerators operate at high enough energies to produce the collisions required to observe the Higgs boson. The only one currently operating is CERN's Large Hadron Collider, a tunnel that's 27 kilometers (17 miles) in circumference and 100 meters (328 feet) underground.
The CMS, or Compact Muon Solenoid, is one detector in the LHC that is specifically looking for the Higgs Boson.
The ATLAS (A Toroidal LHC ApparatuS) project, also at the LHC, is trying to find the Higgs boson.
Experiments at the Fermilab Tevatron accelerator in Illinois also had been searching for the Higgs boson until being shut down. The most recent results of those experiments have ruled out the existence of a Higgs boson with a certain range of mass.
Searches for the Higgs boson also were performed by experiments studying electron-antielectron collisions at the Large Electron Project at CERN in the 1990s.
Q: What's next?
The search for the Higgs boson will intensify with researchers analyzing additional data. Over the course of its lifetime, the LHC is expected to produce 3,000 times more data.
Further research will be needed to understand whether the discovery represents the particle in its simplest manifestation. It's possible there may not be just one Higgs, but a multiplicity of Higgs, ones which haven't yet been seen. More experiments will be able discern its properties more precisely.