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Why are high energies needed in colliders

  1. Nov 26, 2014 #1
    Why are such high beam energies required at particle colliders to produce new physics/particles?
    The Higgs particle has energy of ~MeV so why are ~TeV energies required?
    Furthermore, by what mechanism does the energy get converted into particles/mass?
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  3. Nov 26, 2014 #2


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    The Higgs mass is ca 125 GeV, which is 0.125 TeV. In general, at these energies, the collisions are collisions between the proton constituents and each constituent carries only a part of the full proton momentum and energy.
  4. Nov 26, 2014 #3


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    Those constituent energies can be described with so-called parton distribution functions. It is possible to produce a Higgs at 125 GeV if the colliding protons just have 500 GeV each, but it is very unlikely as you need very high-energetic partons then. At the LHC energy of 4 (later up to 7 TeV) the energy required fraction for the partons is much smaller.

    There is no fundamental "how" (at least not in physics). It just happens.
  5. Nov 26, 2014 #4
    energy conservation. The new particles have rest energy and kinetic energy. The total conservation of energy in the interaction is the "how"
  6. Nov 26, 2014 #5
    There are multiple processes happening at once, it is not the protons interacting, but instead the constituents for a process like the Higgs creation (vector boson fusion, or quark interaction), so part of the reason for the higher energies is that each process gets a fraction of the TeV scale energy.
  7. Nov 26, 2014 #6
    Thanks for the replies!
    So what determines the way that energy is shared between partons? Why does the parton energy distribution change at higher energies and why does a larger total energy allow a smaller energy parton fraction for new particle formation?

    As for the underlying mechanism of energy to particle conversion, how are we able to predict formation rates if we don't know how energy is converted to matter? eg. Why does the probability for an elastic scatter differ from that of an inelastic particle creation?

    Sorry for the bombard of questions..
  8. Nov 27, 2014 #7
    This is determined by the QCD dynamics governing the partons. However, it is a problem to calculate this due to the relevant strong coupling and it is extracted from measurements.
    The distribution describing the probability to have a given parton with a particular fraction of the proton's energy is called the parton distribution functions (PDF's)

    The PDF's don't really depend on the proton energy. They depend on the parton type, the energy fraction it has, and a scale which is used in the calculation.

    If the proton energy is higher the same energy fraction means the parton has more energy and so does the collision in which the particle is created.

    We have a theory, the standard model (which is a quantum field theory) , which can predict the probabilities of different scattering processes to happen, elastic and inelastic.
    Different initial/final states will results in a different probability. Usually the quantity of interest is the cross section.
  9. Nov 27, 2014 #8


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    I am not sure what you are trying to say here:

  10. Nov 27, 2014 #9
    Quantum mechanics is probabilistic.

    So if you know the quantum theory, you can calculate the probabilities of these different interactions (elastic, inelastic, production of particular particles).

    Of course this relies on one understanding the theory, and actually being able to do the prediction. This is why measuring these things experimentally allows to test or constrain the theory.
  11. Nov 27, 2014 #10


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    If you need 10 apples, you can have 10% of 100 apples, or 1% of 1000 apples.
    If you need 125 GeV, you can have 12.5% of 1 TeV or 1.25% of 10 TeV. Same concept.
    Quantum field theory gives the formulas, and they work very well. If those formulas correspond to anything that could be called "reality" is a question for philosophy.
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