1,777 MeV/c 2 (compared to 938 MeV/c 2 for protons and 0.511 MeV/c 2 for electrons ). The top quark (truth quark) is the third- generation up-type quark with a charge of +(2/3) e . [1] It was discovered in 1995 by the CDF and D0 experiments at Fermilab , and