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LEP and other high energy collisions

  1. May 2, 2005 #1
    Just a quick question, has any research instutute such as CERN managed to produce a new stable particle such as a neutron, or even produced and extra electron or proton as a result of colliding electrons and positrons at high energies? or are the untold ?new? but shortlived particles of such a collision just a temporary phenomena.
     
  2. jcsd
  3. May 2, 2005 #2
    What are you defining as stable?

    Every possible decay that has been seen is listed here:

    http://pdg.lbl.gov/2004/listings/contents_listings.html

    Just follow the different decay chains.

    One way to get multiple electrons out is this:

    electron+positron -> 2 charged B mesons -> both B's decay semileptonically (rho0 e nu) -> and then rho0 decays into electron/positron. You'd have 2 electrons and 2 positrons at the end. This particular example would be pretty rare, and is just used for illustrative purposes.

    There are decays that produce p pbar, so yes, you can produce proton/anti-proton pairs out of electron-positron collisions.
     
  4. May 4, 2005 #3
    Thoretically possible - but has it been observed?
     
  5. May 4, 2005 #4

    Meir Achuz

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    I am not sure what your question asks.
    Certainly, protons, neutrons, electrons are produced in high energy colliders.
    Are you looking for a new, different, stable particle?
     
  6. May 4, 2005 #5

    ohwilleke

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    What he is asking, I think, is if anyone has ever observed fermions "condensing" out of the energy produced by a matter/anti-matter reaction, or whether this has only be theorized? Most nuclear reactions involve turning matter into energy, and not the other way around, so most of us are not too familiar with experiments in which energy has "condensed" into matter.
     
  7. May 4, 2005 #6
    Every decay in the particle data book link in my previous post which has a branching fraction (as opposed to an upper limit) has been observed.
     
  8. May 4, 2005 #7

    Meir Achuz

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    You don't need any exotic mechanism. Large numbers of all known particles are produced in high energy e-positron or p-antiprotron colliders.
    A gamma ray hitting a block of lead produces a shower of e's and positrons.
     
  9. May 4, 2005 #8

    ohwilleke

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    A more elementary discussion, which states, yes, quark production from electron-positron annilliation has been observed can be found here: http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

    The entry is titled: "Electron-Positron Annihilation Provides Evidence of Three Colors for Quarks", it states:

    A muon is a "second generation" electron (it decays in around 10^-6 seconds, and its "third generation" cousin the tau, decays in around 10^-13 seconds; the three generations of neutrios, the electron and their anti-particles are the only know "stable" leptons). A hadron is a meson (i.e. quark-antiquark pair) or a baryon (i.e. three quark structure such as a proton or neutron). A list of mensons is found: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/meson.html#c1 and a list of baryons is found: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/baryon.html#c1 All mesons and all baryons other than protons and neutrons are unstable to the point that they decay in 10^-10 seconds or less (often far less), except pions and kaons (both types of mesons), which can sometimes decay over a lifetime as long as 10^-8 seconds.

    The reference given is Rohlf, James William, Modern Physics from a to Z0, Wiley, 1994, Chapter 18.
     
    Last edited: May 4, 2005
  10. May 6, 2005 #9

    vanesch

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    Yes, it is in fact more a pain than anything else ! Especially the loads of fast neutrons are a pain: they degrade detector electronics and are difficult to stop.

    cheers,
    Patrick.
     
  11. May 9, 2005 #10
    Liberated, not created

    Hi Meir,
    "produced" unfortunately intimates creation while the reality is that these high energy colllisions merely liberate particles that are already in the colliding particles.
    In another of your posts you mention Pair Production with photons impinging on a lead block without noting that the energy threshold of the photons is 1.022 MeV. Cheers, Jim
     
  12. May 9, 2005 #11

    Meir Achuz

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    They are NOT already in the colliding particles. All endothermic reactions have thresholds. In the 20 GeV SLAC e^- e^+ collider many particles are produced in one collision. Were they all already in the electron and positron?
    "Produced" fortunately means creation.
     
  13. May 9, 2005 #12
    NOTHING is inside eilther an electron or a positron except a unitary mass surrounded by a plus-1 charged- or minus-1 charged- "halo".
    Please identify just what was created - was it a proton or a neutron - those are the only stable particles that nature creates and that happens at the heart of the Milky Way or any other spiral galaxy. How do you propose that anything besides annihilation occurs; it happens spontaneously without being collided.
     
  14. May 9, 2005 #13

    ohwilleke

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    Nonsense. If you stubbornly refuse to believe in the existence of the standard model, quantum physics and decades of experiments because it isn't "natural" there is nothing I can do to stop you, but the facts fit QCD, QED, and the other basic premises of quantum mechanics.

    Dolly the Sheep, genetically modified crops and dentures aren't "natural" either, but they are all no less real. Also, there is every reason to believe the particles that are not stable in our current environment might have been far more common shortly after the Big Bang and in environments like neutron stars which are outside the realm of ordinary experience.
     
  15. May 9, 2005 #14

    Chronos

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    Last I checked the electron, proton, neutron are the only massive particles that are 'stable' for any appreciable interval of local time - and the neutron is pretty shaky without a proton to buddy up with.
     
    Last edited: May 9, 2005
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