The top quark (20 years after the discovery)
a Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Vorobevy Gory, Moscow, 119899, Russian Federation
b Kirchhoff Institute for Physics, Heidelberg University, Heidelberg, Germany
c Accelerator Physics Center, Fermi National Accelerator Laboratory, Batavia, Illinois, USA
d National Research Center "Kurchatov Institute", Institute for High Energy Physics, pl. Nauki 1, Protvino, Moscow Region, 142281, Russian Federation
e State University of New York, Stony Brook, New York, USA
This paper, written to mark the twentieth anniversary of the discovery of the top quark, offers some insight into how the understanding of this heaviest known particle has developed from prediction through search to discovery to the current knowledge of its production mechanisms and properties. The central role of the top quark in the Standard Model is considered and the window of opportunity it opens for seeking new physics beyond the Standard Model is discussed.