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Where do the particles come from in collisions?

  1. Sep 9, 2008 #1
    I mean, are the particles revealed or are they created? I got to thinking about this when I was reading about the LHC and how they will be able to "find" or "observe" new particles because it can reach higher energy levels. What exactly does this mean?
  2. jcsd
  3. Sep 9, 2008 #2
    Particles are created at random, the chance to create a heavy particle grows quickly with energy. So, for example, Higgs bosons are created occasionally at the Tevatron (if they exist at all), but they are so rare that LHC may create as many Higgs events in a week as Tevatron does in a year. We need to generate a large number of events in order to confirm or deny the existence of the particle. (The way these accelerators work, you can't tell definitively from any given snapshot if you had a Higgs or not) So what would have taken decades or centuries with existing accelerators could be done in a few years at the LHC.
  4. Sep 10, 2008 #3


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    To add to that last post, of course there are also threshold energies for certain processes that create particles. That is, below a certain collision energy, the process is impossible.
  5. Sep 10, 2008 #4
    Well, if you have sufficient energy to create a Higgs, for example, why does it not always pop up? Do they really pop up all the time but are just extremely difficult to detect?
  6. Sep 10, 2008 #5

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    Collisions are probabilistic things. Sometimes one thing happens, sometimes another. The most probable interaction is actually just elastic scattering: the two particles have their trajectories slightly deflected by each other's electric field. Also probable (in proton collisions) are single and double diffraction where one or both protons remains intact, and a small amount of their kinetic energy gets converted into a pion or two. Events where something very heavy is produced, like a top quark or Higgs boson, are quite rare - maybe one in a billion collisions, maybe even less.
  7. Sep 10, 2008 #6
    Yes. You can get any one or more from the whole "zoo" of known elementary particles, and probably many of the unknown ones, just by smashing protons together, provided that you have sufficient energy. But some outcomes will be frequent and some will occur with one-in-a-billion probability. I saw a nice plot showing possible outcomes and their probabilities once, but I can't find it now. Higgs is way, way, WAY at the bottom. And the other problem is that Higgs can't be observed directly, because its so short-living that it decays long before it makes it out of the interaction area and into the detectors.
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