ZBoson

The Z boson, sometimes written as Z0, is a neutral gauge boson in the Standard Model of particle physics. It mediates the weak neutral current and couples to fermions with strengths determined by their weak isospin and electric charge. Alongside the charged W bosons, the Z boson completes the electroweak force description.

In the Standard Model, the Z boson is a massive spin-1 particle that arises from electroweak symmetry breaking. Its mass is about 91.2 GeV, and its total decay width is around 2.5 GeV. The Z couples to fermions through vector and axial-vector interactions, with couplings determined by T3 (the third component of weak isospin), electric charge, and the weak mixing angle. It decays to fermion-antifermion pairs, with hadronic decays forming the majority of the width and invisible decays to neutrinos contributing a significant fraction.

Branching fractions at the Z pole are on the order of a few percent for each charged lepton pair, about 20 percent for neutrino pairs (the invisible width), and the remainder to quark-antiquark pairs. The Z boson plays a central role in many precision electroweak measurements.

Discovery and study: The Z boson was discovered in 1983 at CERN’s Super Proton Synchrotron by the UA1 and UA2 collaborations. Since then, it has been produced and studied at electron–positron colliders such as LEP and SLC, and at hadron colliders including the Tevatron and the LHC. Its properties have been key tests of the Standard Model and probes for new physics.