My question is, what if the mass of the Higgs is 285 GeV, for example, and they are doing collisions at 3 TeV? Does this mean that they are missing the Higgs or just creating a lot of them? In other words, do you have to tune the mass to a critical number to generate particular particles, sort of like a spectrometer uses a diffraction grating? Or is it the case that above a certain mass you get everything below that point?
Hi Olowkow,
There are different ways that a collider can spit out a massive particle, and different colliders (and different particles) behave differently in exactly the way you're asking about. e+e- colliders have one behavior, pp colliders have another.
To make a Z-boson at an e+e- collider, you indeed want the collider to be tuned so the collision energy is equal to the Z mass. To make an Upsilon(4S) meson, you want the collider tuned to the Upsilon(4S) mass.
On the other hand, to make a Higgs boson in an e+e- collision, it turns out that the best reaction to create is one with
both a Z and an H0 in the final state; you want to get your energy up to at least MH + 91 GeV, and somewhat higher is better. So that's a general sort of consideration to think about---are you trying to make a plain Higgs sitting there by itself? Or are you trying to make a Higgs via some sort of top-quark process? You need enough energy to run the whole process.
In any case, the LHC isn't an e+e- collider, it's a pp collider. A proton consists of three "valence" quarks and a sea of gluons and quark-antiquark pairs. In fact, it's tempting to think of it as a quark-quark collider---instead of colliding two protons at 7 TeV each, it'll collide two quarks at about 2 TeV each, 4 TeV total, right? That's a good place to start, but it gets more complicated than that. The sea quarks and gluons (which are much more numerous than the valence quarks) have extremely low energies, even in a 7 TeV proton---most are below 1 TeV. So now your 14 TeV pp collider really behaves kind of like a low-luminosity ~4 TeV
valence quark collider, and also a ~2 TeV quark-gluon collider, and also high-luminosity ~1 TeV gluon-gluon collider. All at the same time. Depending on the Higgs mass, one or the other of these collision types might be the dominant producer of Higgs bosons.
So you don't just want the *proton* energies to be above the Higgs mass. You actually want the *gluon* energies---for as many of those low-energy sea gluons as possible---to be that large.
