Z0bosonen

The Z0 boson, often written as Z0 or simply Z boson, is the neutral gauge boson that mediates the weak neutral current in the Standard Model of particle physics. It is a massive, spin-1 particle with electric charge zero and a short lifetime.

Properties and couplings: The Z0 arises from the mixing of the SU(2)L and U(1)Y gauge fields after electroweak symmetry breaking. Its mass is about 91.2 GeV, and its total decay width is approximately 2.5 GeV. The Z0 couples to fermions through neutral currents with vector and axial-vector components. For a fermion f, the couplings depend on its weak isospin If3 and electric charge Qf, and can be written in terms of gVf = If3 − 2Qf sin2θW and gAf = If3, where θW is the weak mixing angle (sin2θW ≈ 0.231).

Decays and production: The Z0 decays into fermion–antifermion pairs. About 69–70% of decays are to quark pairs (hadrons), while the charged-lepton channels (e, μ, τ) each contribute roughly 3.3%, totaling about 9–10% for all charged leptons. The neutrino channels (three flavors) sum to about 20% of decays, contributing to the Z0’s invisible width. The Z0 can be produced in proton–antiproton or proton–proton collisions via quark–antiquark annihilation, and was studied extensively in electron–positron collisions at LEP and SLC for precision tests of the electroweak sector.

History and significance: The Z0 was predicted by the electroweak theory and discovered in 1983 by the UA1 and UA2 collaborations at CERN. Its properties have been measured with high precision, providing critical tests of the Standard Model and measurements of sin2θW.