What will be the next elementary particle discovered?

Prediction market on manifold. What will be the next elementary particle discovered? To count as a discovery, it must be accepted to exist by the physics community. Note: For this market, I am defining a WIMP as any fermion with mass that interacts via the weak force but not the strong or electromagnetic forces, isn't a neutrino, and isn't the superpartner of some already known particle.

Liquidity: $700. Resolves: 1/1/2051.