Particle Physics in the last 40 years

The 1950s and 60s can be called the golden era of particle physics. The field progressed rapidly during this period both in terms of theoretical ideas and experimental discoveries eventually culminating in the formulation of the Standard Model of Particle Physics.  When I ventured into this field towards the end of the 70s, Top Quark, Tau-Neutrino, Gluon, W & Z bosons and the Higgs boson were not yet discovered and the Standard Model was still incomplete. It is therefore immensely satisfying to see all these particles discovered during my scientific career, over the last 40 years.  These discoveries were made possible due to efforts of thousands of physicists and engineers, including some from this institute. It has also been personally very rewarding to have gotten the opportunity to participate in a few of these experiments which put the Standard Model of Particle Physics on a strong footing.  These milestones, though undoubtedly important, were expected. No one ever doubted the existence of these Standard Model particles.  However, the excitement of an explorer lies in encountering the unexpected, and the new. In that sense, the discovery of neutrino oscillation and its implicit inference that neutrinos have mass is in my opinion the most exciting event in our field during my career. It represents compelling experimental evidence for the incompleteness of the Standard Model as a description of nature and opens up new avenues to explore. The field is still wide open. Grand Unification of fundamental forces, protection of the Higgs mass, neutrino mass ordering, CP-violation in leptonic sector, existence of dark matter are some of the open questions yet to be explored and answered. In this colloquium, I would like to provide you with some glimpses of these discoveries, along with personal anecdotes, and discuss the direction in which the field of particle physics is headed.