Celebrating 20 years of the discovery of the top quark

An historical recount of the events leading to the discovery of the top quark in 1995 by the CDF and DO experiments at the Tevatron. 1 Introduction This presentation brings us back to the early nineties. It is interesting to picture ourselves without iphone and laptops, working on DEC VAX and having to stay in the office to work because there was no internet at home. The programming language was Fortran and plots were made with PAW. Detectors were becoming bigger and more complex, but no Silicon detector had been tried in a hadron collider yet. To put things in perspective for the LHC physicist of today: the MonteCarlo programs of the time did not differentiate between heavy and light quarks (VECBOS), there were no b-tagging algorithms, it was not clear that a Silicon detector could survive the radiation environement of an hadron collider such as the Tevatron and collecting data took a long time (one year for 20 pb-1). Nonetheless, working at the most powerful accelerator of the time was as exciting as it today. 2 History of particles discoveries From the sixties onward the story of particle physics went through a phase of reorganization. First the idea that quarks would be the building bricks of mesons and baryons, then the ap­ pearance of the fact that quarks and leptons seemed to be organized in some sort of families. Discoveries kept confirming this pattern: quark charm in 1974, tau lepton in 1976 and the bound state of the quark b in 1977. By the year 2000 also the tau neutrino was discovered and only one piece seemed missing, the top quark, companion of the bottom quark with charge 2/3. The historical vision gives the impression of necessity of the existence of this quark but that was not the feeling at the time. On the experimental side the search kept giving null result and mass limits increased.