The top is special. It is the heaviest quark by far – more than thirty times heavier than any of the other quarks.
According to the Standard Model, the monsterously heavy top quark should acquire all this mass through its interaction with the Higgs field. The theory tells us that the top is so heavy precisely because it feels the Higgs field more strongly than any other particle.
We can test the theory by making an experimental measurement of the strength of the relationship between the top quark and the Higgs field. To do so we must look at how often a Higgs boson gets spat out when top quarks are produced. This is known as “associated ttH production”, and it has just been measured by the ATLAS experiment at the LHC.
The early results are in and are consistent with expectations – so far. But the uncertainties are very large – about 60% – so there’s plenty of room for something odd to be going on. Any deviations would be very interesting. They might tell us that part of the mass of the top quark came from another source, such as the additional Higgs bosons required by many extensions to the Standard Model.
With more data pouring in all the time, this is a measurement worth keeping an eye on in the future…