Kelly Oakes' winning physics essay in this years Science Challenge:

The standard model describes the behaviour and interactions of all of the most fundamental particles we have seen — and one other particularly elusive one that, physicists hope, we will see in the near future. The model was developed throughout the 20th century and finalised when the existence of quarks, the particles that make up protons and neutrons, was confirmed in the 1970s. At the time many of the particles predicted by the standard model were yet to be seen. Over the years since then, physicists have ticked these particles off, one by one, like items on a shopping list. Now they are left with just one remaining unfound particle — the Higgs boson.