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What's left over after particle collisions, like LHC?

  1. Nov 20, 2013 #1
    I'm curious to know what tends to be 'left over' after particle collisions at sites like LHC. I realize that many different particles may arise, depending on the types of particles used for collision, as well as the kinetic energy put into the experiments. Despite the amazing diversity of outcomes these experiments produce, many of these exotic particles are short lived, and most decay almost immediately. What tends to be left over after the decay process has ceased? Are photons the most likely end-result, or is it electrons and protons, etc? Have we truly created new matter that is stable? I know certain things are supposed to be preserved, but I've never heard a good estimate, of what tends to be 'lying around' after everything happens. Particularly, I am wanting to know if we are creating or destroying matter in the end. Thanks!
  2. jcsd
  3. Nov 20, 2013 #2

    Indeed you end up with a lot of photons.

    Baryon conservations tells you that you must end up with 2 stable baryons. Since you started with two protons.

    Then other than that you have an overall 2+ charge in the form of pions, muons, photons, kaons (i.e. the more stable particles}, of course these end up decaying shortly after or in the detector down to electrons and neutrinos..

    The important thing is that charge, energy-momentum, baryon number etc. are all conserved before and after. In reality it can be complicated if 1 proton collision interacts with another proton collisions. But same rules apply overall.
  4. Nov 20, 2013 #3
    Uhh well, we created antihydrogen at CERN. It was stable. The problem is that it is difficult to keep it away from matter, and it ends up being annihilated. But it indeed was stable and can be called 'new matter', considering the fact there is no antimatter on Earth.
  5. Nov 20, 2013 #4
    At the end of it all you're left with two protons to match the two original protons plus lots of photons, neutrinos, and anti-neutrinos. The photons are absorbed by the medium warming it up and the neutrinos and anti-neutrinos scape. Potentially, other neutral stable particles might be produced (axions?, neutralinos? Other dark matter candidates?) but we don't even know if those particles actually exist. The main point of those experiments is to find that out.
  6. Nov 20, 2013 #5
    Hi All, Thanks for the great replies... So, does it ever happen that we are left with more stable baryonic matter than when we started?? I'm curious because I would like to know if sites like LHC can actually produce matter (like hydrogen). I'm wondering if it's possible to ultimately make atoms from energy. Maybe electrons can be created, which escape, along with the original protons. Thank you!
  7. Nov 20, 2013 #6


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    No. You can change the type a bit - there are nuclear reactions happening in the detector, so you change its isotopic composition. You can even convert protons to neutrons, bound in nuclei to be stable, or neutrons to protons. But the total number of baryons is conserved*. If you create new hydrogen, you have to kill baryons somewhere else (via annihilation of antiprotons and antineutrons).
    New electrons are created, and if that happens via a weak process you can produce them without an positron, increasing the total number of electrons on earth. Charge conservation then tells us that you have to convert a neutron to a proton to keep the balance. The reverse process (kill an electron, convert a proton to a neutron) can happen, too.

    The detector material gets activated and some of those isotopes have very long lifetimes, so the final product (as in: when you shut down the LHC) is not always stable.

    *there are searches for baryon number violation, but they were not successful so far.
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