In January, we reported that CERN was tentatively claiming that Higgs bosons had been created in high energy collisions of hadrons in the Large Hadron Collider (LHC) (“Higgs ahoy!”, Solidarity 229, 11 January 2012).
They were not certain enough that the signals detected were those of Higgs bosons and said they would be searching further this year, after the LHC’s scheduled shutdown and re-opening.
Now, after analysing trillions and trillions more proton-proton collisions, they have come up with enough evidence to have “5 sigma” certainty (99.99997%) that they have discovered the Higgs boson* (or a Higgs boson, since there is a variant on the theory that predicts a family of different sized particles).
The mass of the Higgs is about 126 gigaelectronvolts (GeV), about what was predicted, and about 134 times the mass of a proton.
Wait a second, I hear you say; GeVs are units of energy, not mass. Ah, don’t forget that mass is equivalent to energy, according to Einstein’s equation, E = mc2, and it’s easier to write and say 126GeV than 2.24 x 10-25 kg.
Wait another second, you say; can you just remind me how two protons smacking into each other can make another particle 67 times heavier than both of them put together?
Certainly: the faster things go, the heavier they become — it’s called mass dilation. Usually, the effect is negligible but near the speed of light it becomes appreciable and the protons in the LHC are travelling fast enough that their mass is much higher than that of a Higgs.
What happens is that the protons collide, become converted into a intense burst of energy and then reconvert into all sorts of particles with mass, including some Higgs bosons. Most of these are unstable and break up into other particles which will be detectable. From the latter particles, their masses, charges, speeds and trajectories, scientists infer the existence of the particles formed in the collision. It’s rather like deducing the size of a bullet fired at a vase from the size of the glass fragments, how far they travel and how much damage they cause.
So, if it is the Higgs, why is this important? Well, it provides support for the Standard Model, which describes the fundamental particles from which all visible matter is made. In particular, the Higgs field explains how particles get their mass. Unfortunately, visible matter totals only 4% of all matter, the rest being called, obviously, “dark matter”.
So there’s a lot more to work out. And it may not benefit us directly to know the nature of the universe in more detail but it’s quite exciting and it’s a lot cheaper than bailing out a bank or renewing Trident.
And we’ve already had the internet as a spin-off from CERN’s previous work!
* CERN are being a little cautious about their discovery. It’s definitely a boson and it’s the heaviest one so far found but they won’t finally confirm that it’s the Higgs until they’ve studied it some more.