J/ 𝚿 , fifty years later

The year 2024 marks the fiftieth anniversary of the $J/\Psi$ discovery\cite{J/Psidisc}. The organisers of the DIS2024 Workshop asked me to give a review talk on the significance of this discovery. This article is an edited version of my talk. I want to argue that it was not just the discovery of a new resonance; we knew already a large number of them. It was not even only the first indirect evidence for the existence of a new quark flavor. It was all that, but it was also much more. It was the final proof which convinced the large majority of our community that we were witnessing a radical change of paradigm in our understanding of microscopic physics. From phenomenological models and specific theories, each one applied to a restricted set of experimental data, we had to think in terms of a fundamental theory of universal validity. For most of us this transition was a revelation, for some others it was a painful experience. It is this story that I will attempt to narrate in this note, although I do not consider myself to be an unbiased observer.