Jeremy Bernstein at the NYRB:
The Standard Model, which is a theory of nearly everything (gravity being an exception) likes things in threes. There are, for example, three colors of quarks, just as there were three neutrinos types—until very recently: research conducted by the Mini Booster Neutrino Experiment (MiniBooNE) at the Fermi National Accelerator Laboratory in Batavia, Illinois, suggests the possible existence of a fourth type of neutrino that does not fit into any theoretical model.
Neutrinos have always been my favorite particles, ever since I learned about them in graduate school in the 1950s. They reminded me of that eccentric uncle you’ve never seen, but who you know exists because your aunt speaks of him affectionately as a slightly rogue member of the family. Even the invention of neutrinos is a bizarre tale.
more here.