Colliding beam experiment

from Wikipedia, the free encyclopedia

A Colliding beam experiment ( engl. Collide collide 'and beam , beam ") is an experiment of the particle , in which two counter-rotating beams meet accelerated particles and the shock events are observed between the particles. This differs from the target experiment ; Here a beam of accelerated particles hits stationary matter, the target . In colliding beam experiments, particle reactions can be triggered with significantly higher energy conversions than in target experiments.

Advantage over the target experiment

Before every collision process between two particles, their common center of gravity is always on the straight line connecting the particles, and its location on the straight line is determined by the ratio of the two masses . In a target experiment, it therefore moves towards the target particle until it hits the target. This co-movement of the center of gravity corresponds to an impulse . Since the momentum is a conservation quantity, only those processes occur as a result of the impact in which the center of gravity maintains this momentum in terms of direction and magnitude. It thus also retains a corresponding kinetic energy , and only the remaining energy, the center of gravity energy, is available for conversion into other forms, for example in the mass of newly formed particles (see also kinematics (particle processes) ).

In the colliding beam experiment, the co-movement of the center of gravity can be reduced or almost completely avoided by ensuring that the two particles have almost identical momentum vectors. The center of gravity system then (almost) coincides with the laboratory system , and the center of gravity energy is (almost) equal to the sum of both particle total energies .

Disadvantage compared to the target experiment

The particle density in an accelerator beam is orders of magnitude lower than that of a target, even a gaseous target. The yield of impact processes is correspondingly smaller. Colliding beam experiments therefore require high intensity beams (current strength). However, if the particles rotate on ring-shaped paths, they have not just one but many repetitive “opportunities” to collide.

execution

Colliding beam experiments are carried out on collider systems such as B. the LHC carried out. Usually it is a question of particle- antiparticle collisions ( electron - positron or proton - antiproton ), i.e. particles of the same mass collide. An example of such an experiment is the D0 experiment at the Tevatron .

Colliding beam experiments with colliding partners of different masses, namely protons and electrons, were carried out at the HERA facility . With protons of 920 GeV and electrons of 27.5 GeV, a center-of-mass energy of about 300 GeV was achieved.

Most of the previous colliders (for example LEP , Tevatron , RHIC , LHC and the FAIR, which is currently under construction ) work as synchrotrons and storage rings . In the case of light particles such as electrons and positrons in ring accelerators, however, the synchrotron radiation limits the energy that can be achieved. Collider systems for these particles, such as SLAC and the planned ILC , are therefore often linear accelerators , although only a very small fraction of the accelerated particles can be brought to collision in this way.

literature

  • Povh / Rith / Scholz / Zetsche: Particles and Cores . 8th edition. Springer, Berlin / Heidelberg 2009, ISBN 978-3-540-68075-8 .
  • DA Edwards, MJ Syphers, An Introduction to the Physics of High-Energy Accelerators , Wiley, 1993, ISBN 0-471-55163-5 .
  • Frank Hinterberger, Physics of Particle Accelerators and Ion Optics , Springer, 2008, ISBN 978-3540752813 .