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How fast do particles need to travel to collide?

  1. Mar 11, 2015 #1
    I'm wondering, I always hear how particles in the LHC collide with huge energies, and I'm wondering: how much energy is needed for particles to collide? I mean, if the energies in the LHC are huge and the ones in the RHIC are less huge you have to be able to do it with even less energy, right? So what would happen if particles collided with the minimum necesarry amount of energy? And what if they'd be sent through the tube with less energy than what's required for them to collide? Would they simply go past each other? Or even if they collided, would they just simply stay whole instead of break into smaller particles? Just what would happen if you lowered the energy on particle collisions?
  2. jcsd
  3. Mar 11, 2015 #2


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    There is no minimal required energy for a collision process, but if you want to have something interesting happening (like the production of new heavy particles) you need a lot of energy.

    That has been done decades ago when the accelerators were less powerful, and the results are still useful to understand the collisions now.

    The particle types become more important at lower energy:
    If you shoot a low-energetic electron on a low-energetic electron, they will repel each other a bit and change their flight direction ("elastic collision"), but nothing interesting happens. If you shoot a low-energetic positron on a low-energetic electron (or simply solid matter as this contains electrons), they can still make an elastic collision, but they can also annihilate each other and produce two or more photons.
    Similarly, two low-energetic protons will repel each other and nothing interesting happens, but a proton and an antiproton can annihilate and produce a few new particles (pions).

    If you increase the energy, you can produce more and more heavy particles, and get more interesting physics processes.
  4. Mar 11, 2015 #3
    Thanks so much! Answered all of my questions perfectly.
  5. Mar 14, 2015 #4
    Colliding an electron with a phosphor is the basis for a 20th century TV.
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