Two Z particles in the ALEPH detector

12 November 1997

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The Large Electron Positron Collider (LEP) at CERN, the European Laboratory for Particle Physics, reached new high energies during its run in 1997. This was sufficient to create pairs of Z particles, carriers of the weak force, one of nature's fundamental forces. The Z particle is so heavy it decays almost immediately in a variety of ways. Here one Z has decayed into a quark and an antiquark, which shoot off back-to-back and create opposite "jets" of particles, shown by the sprays of blue and green tracks. The other Z has decayed to an electron and a its antiparticle (a positron) which leave the tracks coloured red and yellow. This contrasts with a previous Picture of the Week where one of the Zs decayed to a heavier version of the electron known as the muon, together with its antiparticle.This image is from the ALEPH experiment, one of four experiments that study collisions at LEP between matter (electrons) and antimatter (positrons).

(The LEP collider and its experiments were shut down to make way for a new machine, the LHC, in November 2000.)

Credit: CERN / ALEPH

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