Boson of Higgs

The boson of Higgs is a Elementary particle whose existence was proposed by Robert Brout and François Englert like by Peter Higgs to explain the crack of the électrofaible unified interaction in two interactions via the Mécanisme of Higgs. It would be also the quantum of the Champ of Higgs. The Boson of Higgs would have given a nonnull Masse to certain bosons of gauge (bosons W and Boson Z) of the électrofaible interaction giving them properties different from those of boson of electromagnetism, the Photon.

The determining experiment will be that which will make it possible to produce a field of Higgs, or its quantum equivalent, the boson of Higgs. Its discovery will be a confirmation of the standard model which predicts it and whose coherence depends on its existence. The boson of Higgs appears only with energy S higher or equal to 115 GeV and one thought a time that it had been highlighted at LEP in 2000. This observation was not very convincing: the statistical significance was too weak. Nevertheless, if it is discovered, this would make it possible to check the concepts of unification and to extend them to a higher field of energy. Currently the lower limit of the mass of boson of Higgs is of 114,4 GeV/c ² (to 95% C.L.). With the lower part of this value, there was no statistically valid discovery. The LHC, which replaces the LEP and will be operational in 2008, will make research of boson of Higgs one of its priorities: if there exists, it should be possible to observe it (with more than 99% C.L.) in less than 5 years, whatever its mass (until approximately 800 GeV/c ²). LHC or the Tevatron (collider proton antiproton) could discover a boson of Higgs which would satisfy the Standard Model or 5 bosons of Higgs (three neutrals and two bearing of the electric charges) according to the prediction of the supersymmetric Model.

The boson of Higgs and the origin of the mass

Which mechanism, in the électrofaible theory, generates the mass of the bosons W⁺, W^- and Z°? Why the photon acquire doesn't mass? Are the masses of the fermions connected to this mechanism? Why the masses of the quarks are so different from/to each other? To try to answer these questions, one introduces the concept of symmetry, and his crack, in the électrofaible theory. The regularities in the behavior of the particles are called symmetries and they are narrowly connected to the laws of conservation. Symmetry is also connected to the concept of invariance: if a change carried out in a physical system does not produce any observable effect, the system is known as invariant with the change, implying a symmetry.

The électrofaible unification is founded on the concept which the forces are generated by the exchange of bosons. When it is said that there exists a force between two fermions (spin 1/2), it is as to say as they are exchanging bosons. It should now be included/understood how the transmitting bosons of the fundamental forces acquire a mass. In does the case of the électrofaible unification, how the W^± bosons and Z° acquire a mass whereas it is not the case for the photon?

Symmetries of gauge require that the transmitters of force (bosons of gauge) are of null mass. To circumvent the problem of the mass of bosons, Salam, Glashow and Weinberg have to invent a mechanism to break the symmetry of gauge allowing W^± and Z° to acquire a mass. Such mechanisms had been developed in other contexts by various theorists: Yoshiro Nambu, Jeffrey Goldstone, Glashow, Peter Higgs and Phillip Anderson. The idea is to postulate the existence of a new field, which one calls field of Higgs.

The field of Higgs is different from the other fields since at low temperature (energy), space prefers being filled with particles of Higgs that not the being. The bosons W^± and Z° interact with this field (contrary to the photon), and advance through space as if they were driven in thick “molasses”. In this manner, they acquire an effective mass. At high temperature (energy), the interactions in the field of Higgs are such as space is not filled any more with these Higgsienne molasses, W^± and Z° loses their mass and symmetry between W^±, Z° and the photon is not broken any more, it is restored. It is said that it is manifest.

The field of Higgs makes it possible to preserve symmetry with high energy and to explain the crack of symmetry with low energy. It is responsible for the mass of électrofaibles bosons, but also interacts with the fermions (quarks and leptons). They acquire a mass thus. Lightest are the neutrinos (until recently, we believed them of null mass), comes then the electron with a mass from 0.511 MeV. All in top of the scale comes the quark signal, which is by far the heaviest elementary particle with its 175 GeV.

The particles (bosons, fermions) acquire a mass because of the field of Higgs, but why each particle acquire does a different mass, or just like does not acquire it mass of in the case of the photon? Why the force of the affinity of the particles with the field of Higgs, what is called the coupling, is so different from one particle to another, and thus how to explain this hierarchy of the masses? Today, one does not know the answers to these questions.

A competition enters the accelerators colliders

The existence of Higgs is too short so that it directly is detected: one can hope to observe only his decay products, even the products of his decay products. Events bringing into play ordinary particles can imitate the signal produced by a boson of Higgs. Studies led to LEP make it possible to conclude with a probability of 8% so that the events observed are explained without utilizing Higgs. However to affirm a discovery in physics of the particles, the probability of error must be lower than 0,00003%.

In the competition between LHC and the Tevatron this one has a length in advance in spite of its maximum energy 7 times weaker: it is already under operation and the background noise of the collisions is less large, the antiparticles (antiquarks of the antiprotons) could generate more specific events, easier to distinguish from the collisions protons protons.

The ideal accelerator would be a collider electron-positron made of two linear accelerators face to face from 500 to 1000 GeV. The ILC ( Internation Linear Collider ) programmed for approximately 2015 would make it possible to include/understand how the boson of Higgs is at the origin of its own mass.

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