Photograph by Patrice Loiez at CERN.

The photograph shows a proton-antiproton annihilation at CERN. (The story below comes from there.)  According to P. Loiez’s explanation, among the byproducts of that annihilation one should be able to make out the traces of the disintegration of an intermediate Z0 boson  into an electron-positron pair. (My untutored guess is that the main central track is the proton and antiproton, the yellow line the electron and positron produced by the desintegration of the invisible Z0.) As in the proton-proton collision of the creation picture, everything in sight is part of the Standard Model, based on the group U(1) x SU(2) x SU(3). Here we also ‘see’ a piece of SU(2), the gauge group of the weak force:  the Z0 particle is one of three basis elements for its Lie algebra.

WR

The first Z particle in the UA1 detector at CERN

On 30 April 1983, the UA1 experiment at CERN first observed the decay of a Z0 particle, the uncharged carrier of the weak force between particles. UA1 recorded collisions between high energy protons and antiprotons, accelerated in CERN's Super Proton Synchrotron. On rare occasions, the proton and antiproton interacted in just the right way to form a Z0. More specifically, a quark inside the proton and an antiquark inside the antiproton came together in an act of mutual destruction known as annihilation, their total energy converting to the mass of the Z0, according to E=mc2.

With a mass of 91.2 GeV/c2 - nearly 100 times heavier than a proton - the Z0 decays almost immediately to lighter particles, but it leaves a characteristic signature in a detector. This computer reconstruction shows the tracks of charged particles thrown out from the proton-antiproton collision at the heart of the UA1 detector. The two white tracks (towards top right, and almost directly downwards) reveal the Z0's decay. They are the tracks of a high-energy electron and an anti-electron (positron). Together they carry the mass of the Z0 converted back to energy, again in line with E=mc2. The other tracks are from particles that formed from the remnants of the colliding proton and antiproton, that is from the quarks and antiquarks that did not form the Z0.

The UA1 experiment was built and run by a team led by Carlo Rubbia, who received the Nobel Prize for the discovery of the Z0 and the related charged particles, the W+ and W-.