Particle physics

Particle physics is devoted to the discipline of physics, the study of the particles. Restricted to this towards the end of the 19th century to molecules, atoms and nucleons, the focus today is on the elementary particles.

In modern particle physics models are checked mainly by Colliding -Beam Experiments at particle accelerators by different particles are successively fired ( for example, electrons on positrons). The resulting reaction products, their distribution in the particles and radiation detectors as well as the energy and momentum balance provide information on properties already known or suspected of "new" species of particles.

These experiments require accelerated particle beams of very high energy. Therefore, it is often spoken of the high energy physics instead of particle physics; this term is however also used for heavy-ion physics experiments at high energies.

When after and were known by more and more particles whose order one turned on their properties, and also began predictions not yet observed particles set up. The current state of particle physics - and many of their predictions - is summarized in the so-called standard model.

Standard Model of elementary particle physics

The present knowledge of the elementary particles and their interactions is summarized in the Standard Model of elementary particle physics. The standard model allows a consistent description of the strong, weak and electromagnetic interactions in the form of quantum field theories.

In the Standard Model particles twelve and twelve antiparticles, which are divided into leptons and quarks exist. The forces acting between these particles are mediated by the exchange of gauge bosons. For the electromagnetic interaction this is the massless photon, the weak interaction, these are the massive W - bosons and the massive Z boson also, while the strong interaction is mediated by eight massless gluons. Also there is the assumption that a graviton could exist, which mediates gravity.

An important difference from the everyday world and ideas of classical physics is that the standard model is very strongly influenced holistic. Connect multiple devices to a single new object, one imagines classic before that the building blocks are still available in the new object and continue to exist there; in a decay of the new object is obtained as in disassembling a Lego model again the original blocks. Even in the standard model of two colliding particles (eg, an electron and a positron) can be combined into a single (eg a photon). The new component is not meant to be composed of the two original, but is again a " indivisible " elementary particles ( i.e. without internal structure). This idea corresponds to the observation that the new particles into particles of other species can decay (eg muons ) than the one from which it originated.

In the Standard Model, the Higgs boson is also predicted. The research facility CERN announced in July 2012 the detection of a particle at the Large Hadron Collider, in which it could be either the Higgs boson. Experts do not expect before the end of 2013 [ deprecated] clear evidence that this is certainly to the Higgs boson. If the evidence of the Higgs boson does not succeed with this particle, the theory of the existence of the particle would have to be discarded. Through the Higgs mechanism ( the absolutely the existence of the Higgs boson related) could be explained theoretically elegant, why (almost) all other particles are not massless (such as the photon ), but have a mass.

It is clear from theoretical considerations, that the Standard Model above certain particle energies can not provide a correct description of the world. For this reason, extensions of the standard model were also no empirical data that indicate a failure of the standard model, developed. Of here the supersymmetry and string theory are mentioned.

Experimental Particle Physics

In particle scattering experiments are performed, usually in the form of Colliding -beam experiments.

The largest international laboratories for particle physics are:

• CERN on the French- Swiss border near Geneva. The main accelerator are the now dismantled LEP ring ( Large Electron-Positron Collider) and LHC (Large Hadron Collider).
• DESY in Hamburg ( Germany ). Main accelerator was HERA ( decommissioning on 30 June 2007). Here electrons or positrons with protons were brought to collision.
• Fermilab, near Chicago (USA). Main accelerator was the Tevatron (shutting down on September 30, 2011), brought the proton antiproton collision.
• Brookhaven National Laboratory, Long Iceland (USA). Main accelerator is the RHIC ( Relativistic Heavy Ion Collider ), which brings heavy-ion collision (eg gold ) or protons.

In addition, there are many other particle accelerators which operate depending on the physical question in different energy ranges.