You’re making me angry. You wouldn’t like me when I’m angry. -Bruce Banner
Hey, LHC, what did those protons ever do to you? You take them, accelerate them to the fastest speeds we’ve ever accelerated protons to on Earth, and then smash them into one another with more energy than ever before!
The Large Hadron Collider takes bunches of protons, accelerates them in opposite directions inside its giant ring, and smashes them together — ideally — at the centers of these giant detectors.
At Fermilab, each proton would come in with an energy up to about 1.0 TeV, for a total collision energy of 2.0 TeV. Each TeV, remember, is a Tera-electron-Volt, or 1012 electron-Volts.
At the LHC, they just broke that record, as each proton came in with an energy of 1.18 TeV, for a total of 2.36 TeV. In theory, the LHC can support a maximum energy of 7 TeV for a total of 14 TeV, although practically it won’t get there anytime soon.
So you might reasonably ask yourself the following:
Why do I need all that energy to find the Higgs, which should have a mass that needs less that 0.2 TeV of energy to create?
I mean, wouldn’t it make sense that Fermilab should’ve found the Higgs already? It’s just a question of energy, isn’t it?
Well, it’s only a little bit more complicated than that. Your reasoning would be perfect if — instead of protons — you were colliding electrons with positrons.
Before they had the LHC (the Large Hadron Collider), they had LEP (the Large Electron-Positron… collider) in the same underground tunnel! They made many discoveries there, including the Z0 boson, but only got up to 110 GeV of energy total.
But there’s a big difference between electrons and protons. Electrons are — as far as we can tell — just points with mass and charge. You smash a 55 GeV electron with a 55 GeV positron, and you’re guaranteed to get 110 GeV of energy available to create new particles, whether they’re photons, bosons, quarks, or anything else.
But protons don’t work that way. Protons are made up not only of three quarks each, but also countless gluons and many sea quarks. Although each proton may have a tremendous amount of energy, it isn’t the protons, per se, that collide. It’s just a single quark or gluon inside each proton that goes “smash!”
Well, each collision, if you’re lucky, will give you maybe 10% of the total energy available for creating new particles. So you can get to higher energies with protons than electrons, but they’re also far less efficient. They’re also significantly messier! The top image is what a proton-proton collision looks like, while an electron-positron collision looks like this:
So clean in comparison! But so limited in energy, too. So we can get more energy, eventually, out of proton-proton collisions. But the trade-off is that you have to put a lot more work in to get the same results as electron-positron collisions, including sifting through billions of useless collisions to get the one useful one.
So be patient; it’s going to take a long time for any new discoveries to come to light. But the payoff? If the Higgs exists, the LHC is going to find it!
(Eventually.) Good luck to everyone over there; I hope to hear the good news soon! In the meantime, smash away!