Here you get back to the opening page of the Z-Path. This is in agreement with all current observations, and is therefore a highly valuable result, placing the Z boson in theory and in Nature exactly where it needs to be for our world to look like it does. This information has proven that, at current energies, there are exactly 3 types of neutrino species and, thereby, 3 families of leptons and quarks. One of the big achievements of the LEP experiments was the precise measurement of all observable Z decays (to charged leptons and to hadrons, which has been used to extract information about Z decay into neutrino-antineutrino). In order to reproduce reality the theory behind weak interactions dictates the way the Z boson (and the W's) should behave. The Z and the W bosons mediate all phenomena governed by weak interactions. LEP was actually nicknamed the Z-factory! The Z boson is a necessary part in the jigsaw puzzle, which makes up our theory of elementary particles and their interactions. The Z boson has been measured extremely precisely at the earlier particle accelerator at CERN, the LEP (Large Electron-Positron Collider). Have a look at the Feynman diagrams of the electron-positron and muon-antimuon decays of the Z. Follow this link to learn about Feynman diagrams. Physicists use Feynman diagrams to visualize particle production and decay. "Luckily" we will only concentrate on two of the easiest detectable decay-modes, the decay into electron-positron or muon-antimuon. This gives a total of 24 decay possibilities, but only 21 visible. (muon) lepton decay into three body through the new Z current and the diagram for e. Adding up the 6 quark-types (up, down, charm, strange, top, bottom) each with 3 colours results in 18 decay possibilities. from publication: Charged lepton mixing processes in 331 Models.Quarks have a property we call "colour", and each quark comes in 3 colours. These appear as particle showers called “jets“ in the detector. In 70% of Z decays, a quark-antiquark pair is produced.The neutrino decays gives another 3 possibilities.The neutrinos are therefore invisible to us and the only way we can “see” them is when we measure that there is some energy or transverse momentum missing after the collision (since we know that both transverse momentum and energy should be conserved in the collision). Our detector is not capable of detecting neutrinos since they almost don't interact with anything (no electric charge). The Z boson decays in 20% of the cases into a neutrino-antineutrino pair. Each pair is approximately equally probable. The three possible charged lepton pair types are electron-positron, muon-antimuon, and tau-antitau pairs. In 10% of the Z-decays, charged lepton-antilepton pairs are produced. The 100% probability of Z to decay is divided between groups of particles according to additional conservations laws. Therefore Z must decay into a particle, antiparticle pair. This is because in nature charge is conserved. Since Z is neutral the sum of the charges of its decay products must be 0. Let's look a bit closer at how the Z particle can decay once it is produced. The exchange/carrier particles mediating weak interactions are the charged W +, W - and the neutral Z.
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