Z boson
|
Z 0 |
|
|---|---|
| classification | |
|
Elementary particle boson gauge boson |
|
| properties | |
| electric charge | neutral |
| Dimensions | (1.626 · 10 −25 ) kg |
| Resting energy | (91187.6 ± 2.1) MeV |
| Spin | 1 |
| average lifespan | 2.6 · 10 −25 s |
| Decay width | (2495.2 ± 2.3) MeV |
| Interactions |
weak gravitation |
The Z boson ( symbol ) is a gauge boson and therefore an elementary particle . Like its related W boson, it mediates the weak interaction . While the W boson is electrically charged , the Z boson is neutral. It is its own antiparticle .
Similar to the photon , but different from the W bosons , the Z boson mediates an interaction between particles without changing their type (more precisely: flavor ). While the photon only mediates forces between electrically charged particles, the Z boson also interacts with the uncharged neutrinos .
Discovery story
The Z boson is responsible for the neutral currents . These were predicted in the context of the Unified Theory of Electroweak Interaction in the 1960s by Sheldon Glashow , Abdus Salam, and Steven Weinberg (who received the 1979 Nobel Prize in Physics for this theory ) and shortly afterwards with the Gargamelle experiment at CERN on the elastic neutrino - Scattering from electrons observed.
The direct detection of the Z boson was not until 1983, when after a reconstruction of the Super Proton Synchrotron into a proton - antiprotons - Collider sufficient mass energy was available. Detectors UA1 and UA2 were set up to detect the W and Z bosons . Carlo Rubbia and Simon van der Meer received the Nobel Prize for this in 1984.
Sample reaction
One reaction in which the Z boson plays an important role is, for example, the following detection reaction for solar neutrinos, which does not depend on the neutrino type:
The Z boson thereby transfers as much kinetic energy of the incident neutrinos to a nucleus of deuterium that the binding energy of the core can be overcome and he into a proton and a neutron decays. This reaction in particular is used in the Sudbury Neutrino Observatory to detect solar neutrinos. There is heavy water in a large tank that contains many deuterium nuclei.
Other example reactions of the Z boson can be found under electroweak interaction .
Decay channels
The Z boson decays preferably into hadrons with approx. 70% , furthermore with approx. 10% in pairs of charged leptons (e + e - , μ + μ - or τ + τ - ) and with approx. 20% in particles that cannot be detected in the particle detectors of collider experiments. Since it is assumed that these undetectable particles are the light neutrinos, the exact measurement of the total and partial decay widths of the Z boson also allows the number of generations of the neutrinos to be determined. The evaluation of current experiments gives a value of 2.92 ± 0.05, which agrees well with the three neutrino generations known so far.
The physicist Steven Weinberg called the additional particles Z-particles ; Bosons were named after the Indian physicist Satyendranath Bose .
Individual evidence
- ↑ C. Patrignani et al. (Particle Data Group): Review of Particle Physics . In: Chin. Phys. C . tape 40 , 2016, 100001, doi : 10.1088 / 1674-1137 / 40/10/100001 .
- ^ The Nobel Prize in Physics 1979 . Nobel Foundation. Retrieved Jan. 5, 2010.
- ↑ Dieter Haidt, DESY: The discovery of the weak neutral currents ( English ) CERN Courier. Oct. 4, 2004. Retrieved Jan. 5, 2010.
- ↑ Pierre Darriulat: The W and Z particles: a personal recollection ( English ) CERN Courier. Oct. 4, 2004. Retrieved Jan. 5, 2010.
- ^ The Nobel Prize in Physics 1984 . Nobel Foundation. Retrieved Jan. 5, 2010.
- ↑ K. Nakamura et al. (Particle Data Group), J. Phys. G 37, 075021 (2010), Particle Listing - Z-Boson (PDF; 411 kB)
- ↑ K. Nakamura et al. (Particle Data Group), J. Phys. G 37, 075021 (2010), Review - Number of Light Neutrino Types from Collider Experiments (PDF; 41 kB)
Web links
- What are W&Z bosons? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on Aug 2, 2006.