What a tiring yet exciting night for the physics community. After fifty years of searching for the elusive Higgs boson and completion of the Standard Model of particle physics, the two teams at the Large Hadron Collider announced that they had in fact discovered the Higgs. It is fairly certain now that they team leaders (and probably the theorists who developed the model) will be getting a Nobel Prize for this discovery very soon.

As I just wrote a review of the Higgs mechanism yesterday, I won't repeat it here. However I will provide some information on the discovery itself.

First off, it is a 5 sigma signal. Without going into a full review of statistics, that simply means that it is a very confident discovery. A 1-sigma signal means that you are about 84% certain of the result, or in other words if you repeated the experiment six times, one of them would give a false positive. A 2-sigma signal is about 97.5% certain that the discovery is real, and a 3-sigma is 99.9% certain. This is a 5-sigma signal, which is only wrong one time in 3.5 million experiments, or is 99.99998% certain!

The manner in which it was discovered is also interesting. The Higgs leaves no real effect on the detectors, and it decays away far too quickly to ever be seen directly anyway. But the basic Higgs model has very well defined probabilities for being produced in high energy collisions and well understood decay rates to other particles that can be detected. So the LHC collided billions and billions of protons together, and then the teams counted how many of these collisions produced each type of detectable particle. We can easily calculate how many and what type of particles are produced without a Higgs and with a Higgs. When the collisions were analyzed, it showed the predicted rates for a Higgs model.

Second, when the Higgs (or any particle) is produced and decays with a certain combination of energy and momentum (specifically when the mass, energy, and momentum satisfy E^2 – p^2 c^2 = m^2 c^4), the process becomes far more efficient and the number of detectable particles is increased. So by analyzing the energies of the particles, and looking for peaks in their energy distribution, the mass of the Higgs can be determined.

The LHC found the Higgs to have a mass of 125GeV (which happens to be almost where I was guessing it to be in my dissertation :) ). For comparison, a single hydrogen atom weighs about 1GeV and 125GeV is roughly the weight on a single atom of Iodine or Xenon. Except the Higgs particle is many orders of magnitude smaller than these atoms, and it has no internal structure (or at least none that is known yet)

So after fifty years of searching and countless hours and dollars spent on experiments, the Higgs has finally been found. The Standard Model of particle physics is now complete. Now we start exploring new frontiers of physics....