Higgs Facts

Since the opening of the Large Hadron Collider in 2008, and especially within the past month, there has been a lot of interest in the media about the Higgs Boson.  But what is it?

It is usually said that it is the Higgs Boson that gives stuff mass, but that isn't quite right.  So let's get our facts straight.  Much like a gravitational field, or an electromagnetic field, the Standard Model says there is a Higgs Field.  The difference is that the Higgs field has the same strength everywhere.  Fundamental particles (such as quarks and leptons) are able to interact with this field, some more strongly than others.  It is this interaction that gives these particles mass.

Then, if you add the mass of the quarks to make a proton or neutron... you don't come close to the total mass of the larger particles.  In our world of the large, we are used to the mass of the whole equaling the sum of its parts.  At this atomic level though, the mass of the parts is tiny compared to the energy holding those parts together.*  And we should know that from E = mc² that mass and energy is really the same thing.  In fact, physicists measure particles in electronvolts, an amount of energy.  A proton has nearly 1 GeV, but the three quarks only have a combined mass of around 10 MeV, or about 1%.  So, no, even without the Higgs Field, we would still have mass.

So, we've talked a lot about this Higgs Field.  But what is this Higgs Boson supposed to be?  Much like the Photon exists as a particle representing the electromagnetic field, the Higgs Boson is a particle representing the Higgs Field.  If physicists could discover the Higgs Boson, that would show that the Higgs Field exists.  It was predicted to have much more mass than the other particles, and could only be discovered in a high-energy particle accelerator.

A particle accelerator works by speeding protons to near the speed of light.  As the protons collide, this kinetic energy is converted into mass and all this exotic matter appears until it decays into stable particles.  The Higgs Boson was predicted to decay so quickly that it couldn't be directly measured.  Instead, physicists measure the particles that it decays into, and if there were an unexpected spike in the graph, they would know they had something generating these extra particles.  On July 4th, 2012, scientists at the Large Hadron Collider announced that they had seen such a spike with enough statistical significance to announce a discovery.

As with any discovery, scientists are cautious.  Even though they have definitely found a particle with about 125 GeV, in the range they were expecting, they cannot say whither it is actually the Standard Model Higgs Boson.  They still need to see if it has all the properties they expect, not just the mass.  But until then, we are all very excited with this discovery, and are looking forward to how things go from here.

*Technically, its gluons holding the quarks together, but gluons are massless, and it is again the energy we are measuring here.