First collisions

First Z decay into hadrons recorded by OPAL and LEP on 13 August 1989 at 23:17
Première désintégration de boson Z en hadrons enregistrée par OPAL et LEP le 13 août 1989 à 23:17 (Image: CERN)

The OPAL experiment recorded the very first collision at 23:17 on 13 August 1989 and the other three experiments followed soon after.

Timeline
The Large Electron–Positron Collider