Threshold energy

Threshold or threshold energy is in particle energy (rest and exercise energy) called, from which a particle can occur real.

If you shoot two particles to each other, they have an energy which is composed of the mass of the two particles plus the relative kinetic energy. If it is allowed in principle in such a collision that a particular third particle is created, it is crucial whether this total energy of the collision above or below which is the rest energy of the third particle. If the total energy below the third particle can occur virtually. Then it is again divided, before it can be recorded in any one detector. In the other case, the third particle can result in real and measured in a detector. This point, which corresponds to the rest mass of the third particle, called Threshold.

For example, the electron and positron Z0 ( Z boson ). The threshold energy here is about 90 MeV. That there is Z0 in principle, but is below 90 MeV have important because a photon 90 is also formed below MeV not from any electron / positron collision. Sometimes a Z0 is produced and decays again. In the detector results this shows the rates of the final states, which differ from those of pure photoproduction.

• Particle Physics