The Z boson, together with the W boson, is the mediator of the weak interactions. When a particle emits or absorbs a Z boson, it does not change its nature (an electron remains an electron, an up quark remains an up quark). In many aspects, the Z boson interacts with the other particles in a similar way to the photon. This shows that, at high energies, the weak and the electromagnetic forces can be unified into the electroweak force.
The first hint of a weak neutral interaction was found in the 1970s at CERN with a bubble-chamber detector. Here, the passage of charged particles in the form of small bubbles in a liquid is observed. The detector was exposed to a flux of neutrinos, which by exchanging a Z boson with the electrons of the liquid, gave them a push, so that they could be observed as a trace in the detector.
Based on this evidence, an accelerator (SPS) at CERN was modified to bring protons and antiprotons into collision. Exploiting new types of detectors to study these collisions, the Z boson (together with the W boson) was discovered in 1983. The Z boson can be produced even more specifically by colliding high-energy electrons and positrons with a total energy corresponding to the mass of the Z boson. This was done at CERN from 1989 to 2000 with the Large Electron Positron (LEP) collider (part of which is on the Einstein Terrace). The Z boson appears as an elevation in a plot like the one shown on the sign, where the Z boson and lighter particles can be seen as peaks.
