Laboratory of Frascati in Italy joined the collaboration. The collaboration completed a conceptual design report for CDF in the summer of 1981, and construction on the collision hall began on July 1, 1982. The lab dedicated the CDF detector on October 11, 1985, and CDF observed the Tevatron's first proton-antiproton collisions on October 13, 1985. Over the years, two major updates were made to CDF. The first upgrade began in 1989 and the second began in 2001. Each upgrade was considered a "run". Run 0 was the run before any upgrades (1988-1989), Run I was after the first upgrade, and Run II was after the second upgrade. The upgrades for Run I included the addition of a silicon vertex detector (the first such detector to be installed in a hadron collider experiment), improvements to the central muon system, the addition of a vertex tracking system, the addition of central preradiator chambers, and improvements to the readout electronics and computer systems. Run II included upgrades on the central tracking system, preshower detectors and extension on muon coverage. CDF took data until the Tevatron was shut down in 2011, but CDF scientists continue to analyze data collected by the experiment. Discovery of the top quark One of CDF's most famous discoveries is the observation of the top quark in February 1995. The existence of the top quark was hypothesized after the observation of the Upsilon at Fermilab in 1977, which was found to consist of a bottom quark and an anti-bottom quark. The Standard Model, which today is the most widely accepted theory describing the particles and interactions, predicted the existence of three generations of quarks. The first generation quarks are the up and down quarks, second generation quarks are strange and charm, and third generation are top and bottom. The existence of the bottom quark solidified physicists’ conviction that the top quark existed. The top quark was the very last quark to be observed, mostly due to its comparatively high mass. Whereas the masses of the other quarks range from .005 GeV (up quark) to 4.7GeV (bottom quark), the top quark has a mass of 175 GeV. Only Fermilab’s Tevatron had the energy capability to produce and detect top anti-top pairs. The large mass of the top quark caused the top quark to decay almost instantaneously, within the order of 10−25 seconds, making it extremely difficult to observe. The Standard Model