Calorimeter (particle physics)
In particle physics is meant by a calorimeter an instrument for measuring the total energy of a single particle. In particle physics experiments, the calorimeter is an essential component of Teilchendetekors.
The incident, fast particles in the calorimeter axis is decelerated to zero velocity, while the energy released is determined. Upon incidence of high-energy particles in a calorimeter arise secondary particles generate themselves while other particles until the available energy is exhausted. This cascade of Sekundärteilchenerzeugung is called particle showers. Frequently in a calorimeter also a ( approximate ) location information is in addition to the energy determined.
Traditionally calorimeter are distinguished according to the nature of the predominant interaction.
An electromagnetic calorimeter is used for determining the energy of particles which interact substantially the electromagnetic force. These are electrons and positrons and gamma particles ( high-energy photons), to a lesser extent also muons.
Particularly well enables the functions of a so-called Sandwichkalorimeters explain, are alternately arranged in the layers of absorber and reading material. In the absorber, a series of bremsstrahlung and pair production processes developed (each proportional to the atomic number Z ²). An incident on the absorber electron emits a photon, the photon is an electron-positron pair, which again radiates photons, etc. The process continues as long roughly until all electrons have reached the critical energy Ek and then mainly by ionization emit energy. A part of this ionization energy is measured with the layered intervening read material ( scintillator ).
Be E0 is the energy of the primary particle, so the number of shower particles thus yields to:
In the simplest model it is assumed that each doubled after a radiation length χ0 the number of particles. Then you have at the end of the shower after n radiation lengths particles with energy Ek. The number n of lengths of radiation is:
The shower depth therefore increases only logarithmically with primary energy:
The unit of length is χ0 the radiation length. As the number of shower particles N is proportional to the energy, the error of N, however, the result is:
The relative error is therefore smaller with increasing energy. For magnetic measurements of the pulse, however, he rises with the energy to (because the curvature is always lower). Therefore only calorimetric measurements are possible at energies in excess of about 10 to 20 GeV and with charged particles.
Types of electromagnetic calorimeter
- Lead glass calorimeter ( eg in the CMS detector at the LHC at CERN ).
- Liquid noble gas calorimeter ( eg in the ATLAS detector at the LHC at CERN ).
- Sandwich calorimeter consisting of alternating layers of scintillators and absorber materials (eg, in the ZEUS calorimeter at HERA at DESY ).
In a hadronic calorimeter to particles can be detected, which are mostly subject to the strong interaction. [A 1] Since hadronic particles scintillating material penetrate almost unhindered, a structure as in the electromagnetic calorimeter is not possible. Therefore hadronic calorimeters are designed as "sampling" calorimeters in layers Often, with sensitive detection layers alternating with insensitive, only the energy loss serving layers. In these absorbers the interaction processes of hadronic particles take place, which then produce electrons, photons, hadrons and nuclear fragments; these in turn are detected in the subsequent sensitive layer by producing scintillation light.
Research and Development
With the ever -increasing energies and intensities in particle physics, the demands of quality, complexity, and radiation resistance [A 2], the detectors whose main component is the calorimeter. The development and construction of this particular detector component has become an independent branch of science.