|The Large Hadron Collider. Nothing to see here. Please move along.|
Here's a list of major discoveries, in reverse order:
2012: The Higgs boson. This won a well-deserved Nobel Prize a year later. But it was certainly not a "surprise." The Higgs boson was the last missing piece of the standard model of particle physics. It would have been more surprising if it hadn't been discovered.
1995: The top quark. Matter is composed of 6 particles, called quarks, and this was the last one to be discovered. It was unexpectedly massive, but certainly no surprise -- everyone was confident that it was out there somewhere.
1983: The W and Z bosons. These were certainly a major discovery, but they had been predicted earlier to explain the weak interaction, which is responsible for nuclear beta decay. So I would not call their discovery unexpected.
1977: Discovery of the bottom quark. There were good reasons to think the bottom quark existed, so no surprise here.
1975: And here's our most recent surprise at a particle accelerator: the tau particle. The particles we observe seem to be duplicated in "families" of particles, but until this discovery, it looked like there were only two families. The tau was the first evidence for a third family (which was then completed with the aforementioned discoveries of the bottom and top quarks).
That's right, the most recent unexpected particle to turn up at an accelerator was in 1975. In retrospect, my high school years (1973-77) were something of a golden age for particle physics. I remember reading about these discoveries in the pages of Scientific American and thinking that this was just the normal progress of science. Little did I know that I wouldn't see the likes of it again for 40 years. I certainly haven't given up hope that the Large Hadron Collider will turn up something totally unexpected. I just hope they do it before I retire. Or die.