Neutrinos are indeed fascinating particles, but it's important to note that they are not the smallest particles in the universe. Neutrinos are elementary particles with extremely low mass and no electric charge. They belong to the lepton family, which also includes electrons, muons, and taus.
Detecting neutrinos is a challenging task because they interact very weakly with matter. However, several detection methods have been developed to observe neutrinos indirectly. The most common method involves building large underground detectors, such as the Super-Kamiokande in Japan or the IceCube Neutrino Observatory at the South Pole. These detectors are filled with a medium (water or ice) that can produce flashes of light when neutrinos collide with atomic nuclei or produce charged particles that travel faster than the speed of light in the medium. By observing these flashes of light or detecting the charged particles, scientists can infer the presence and properties of neutrinos.
Regarding the existence of other small and strange particles yet to be discovered, it's an ongoing area of research in particle physics. The Standard Model, our current theoretical framework describing elementary particles and their interactions, has been remarkably successful in predicting and explaining the behavior of known particles. However, it is known to be incomplete. There are several unanswered questions, such as the nature of dark matter, the matter-antimatter asymmetry in the universe, and the unification of fundamental forces.
Many theories beyond the Standard Model, such as supersymmetry and string theory, propose the existence of additional particles and new phenomena. These hypothetical particles include supersymmetric partners of known particles (such as neutralinos), sterile neutrinos, axions, and others. Experimental efforts are underway to search for these elusive particles using particle colliders, underground detectors, and astrophysical observations. The discovery of such particles would provide valuable insights into the fundamental nature of the universe and could potentially revolutionize our understanding of particle physics.