Do high energy collisions ever produce new, stable matter?


by hkyriazi
Tags: collisions, energy, matter, produce, stable
hkyriazi
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#1
Nov23-12, 09:00 PM
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The title says it all. I'm contrasting "stable matter" with short-lived particles that quickly decay into something else. (The E=mc2 equation implies that it's possible, but in terms of stable matter, I'm familiar only with it being destroyed, say, in nuclear explosions.) Are ordinary (stable) electrons/positrons or nucleons ever created de novo this way?
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Vanadium 50
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#2
Nov23-12, 09:13 PM
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Sure. All the time.
hkyriazi
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Nov23-12, 09:33 PM
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Quote Quote by Vanadium 50 View Post
Sure. All the time.
Can you give me a reference? Even a textbook would be fine. (Honestly, I did do a google search, and read through some Wikipedia articles on high energy physics, particle accelerators, etc., to no avail, prior to posting this question.)

jtbell
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Nov23-12, 10:14 PM
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Do high energy collisions ever produce new, stable matter?


How about electron-positron pair production?

http://teachers.web.cern.ch/teachers...n-positron.htm
Vanadium 50
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#5
Nov24-12, 07:37 AM
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The PDG (pdg.lbl.gov) has tables upon tables on how often protons (to pick one example) are produced in various collisions.
mfb
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Nov24-12, 08:35 AM
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All produced particles decay to stable particles after a while (and with the exception of neutrons, within microseconds or less). Some decay to just photons, but all other end up producing electrons, neutrinos and protons and/or their antiparticles.
Some stable particles are produced in the initial collision as well.
hkyriazi
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#7
Nov24-12, 11:41 AM
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Thanks, folks. The electron-positron pairs were nice, especially with some being produced from x-ray energy. I couldn't fathom the notation of the Particle Data Group tables, though.

Please permit me to refine my question a bit.

Are protons (or antiprotons) ever produced from gamma rays, or anything other than other baryons? The Wikipedia article on antiprotons gives this equation for their formation in cosmic ray proton collisions with nuclei:
p + A → p+ p +p+ A
(the middle "p" is supposed to have a line over the top of it, indicating the antimatter version of the proton, but, not knowing how to do that here, I underlined it instead). But I'd like to know if the nucleus (A) the high energy proton collides with is the same afterward (thus acting merely as a catalyst), or if it has two less nucleons (one for each of the new nucleons).

In other words, do we ever see baryons arising de novo from photon energy in the lab?
mfb
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Nov24-12, 02:08 PM
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##e^- + e^+ \to p + \bar{p} (+X) ## is possible, for example. Together with the proton, an antibaryon has to be produced due to baryon number conservation.
LEP (DELPHI) publication talking about proton production

##\gamma + X \to p + \bar{p} +X'## is possible, too.
LEP (L3) measurement of proton-production, where photons as intermediate states are discussed.

Heavy ion collisions produce many new baryons and antibaryons.
Pion, Kaon, and Proton Production measured at ALICE. A central lead-lead-collision at LHC energies produces (on average) >10 protons/antiprotons (more like ~100) if my estimate based on figure 1 is correct.
hkyriazi
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#9
Nov25-12, 12:24 PM
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Thanks, mfb! And, I now also know how to produce a ## \bar{p} ##. ;-)


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