The Higgs

A friend asked me to explain the implications of the current Higgs hoo-ha in a tweet. I failed. This was the shortest I could manage! Let me know if any of it is too terse…

The Higgs boson is the only particle in the ‘standard model’ of particle physics which we aren’t 100% certain exists. There are two types of particle in the model: fermions, which are ‘stuff’ (eg electrons, and the quarks which make up protons and neutrons); and bosons, which transmit forces (eg photons, which are particles of light, and transmit electromagnetic forces). The Higgs boson is one of the latter and, if it exists, would be responsible for giving particles mass. The theory says that the Universe is filled with a sticky soup of Higgs particles, and those particles which interact most strongly with these Higgses are bogged down by them. This is what we think of as mass—a tiny, light electron barely sees the Higgs particles, whilst a quark (the tiny particles which make up, amongst other things, protons and neutrons) is wading through a dense sea of them.

Physicists spot new particles by looking for their decay products. They carefully catalogue the showers of daughter particles which follow a collision in the LHC, and effectively draw dotted lines back to look at where they came from. They then see how many particles came from one specific point, and add up their masses to find the mass of the particle which was originally there. What the guys and gals at CERN are seeing is a large, discovery-quality excess of points where a specific mass seems to be. This might be the Higgs. In order to be sure it’s the kind of particle we’d call the Higgs, rather than just a totally left-field discovery, we need to do more detailed analysis of the kinds of particles it decays into, and how often it decays into each. If this matches the signature of the Higgs, that’s almost certainly what we’ve got—and in fact, given where we’ve been looking in order to find it at all, this already looks fairly likely.

If this new particle is definitely the Higgs boson, it would be the last piece in the standard model’s mathematical house of cards, and we’d have a very large section of the Universe tied down with theory. However, it’s not the end of physics: the standard model explains very well how small numbers of fundamental particles interact, but it can’t describe how huge collections of particles work together (from solids and liquids to the Earth’s atmosphere); gravity (which is rather important!); or, even in particle physics, the weirdest, tiniest fermions we know of called ‘neutrinos’.