On a pleasant discovery
The discovery of the fourth kind of quarks named charmed (or c) quark in 1974 has suggested this isn’t all and reinforced the belief that there should be at least two another kinds of heavy quarks which make up the third generation of quarks. An additional argument in favor of that was the discovery of a lepton belonging to the third generation of leptons — the tau lepton. The charmed quark’s mass is several hundred times higher than that of the first generation quarks — the up and down quarks comprising nucleons and pions. Therefore, one might expect the mass of the next, the fifth quark would be enormous, which would delay discovery of it. However, the next, bottom quark appeared to be only three and half times heavier than the charmed quark and was registered three years later. Furthermore, since lifetime of a quark is inversely proportional to its mass squared, it was expected that mesons containing a new quark, B mesons, decay too quickly. But after another three years, these have been discovered and, to everyone’s surprise, their lifetime is not less than that of mesons containing the charmed quark, D mesons, as if the nature has especially taken care of the convenience to study them.