Complex sentence: Throughout the 1950s and 1960s, improvements in particle accelerators and particle detectors led to a bewildering variety of particles were found in high-energy experiments and the term "elementary particle" referred to dozens of particles, most of them unstable.
Split into simpler sentences: Throughout the 1950s and 1960s, improvements in particle accelerators and particle detectors led to a bewildering variety of particles found in high-energy experiments. The term "elementary particle" came to refer to dozens of particles, most of them unstable.