Monday, January 5, 2015

particle physics - Pair production of quarks


I was reading about pair-production of particles by photons, and in every place that I read, only the electron/positron production was said. So I had the following doubt, is it possible to have a quark/anti-quark pair production? if yes, how?



Answer



Yes, pair production is possible for quarks in the same way that for electrons or muons. But there are two caveats:




  • QCD has a nasty property called confinement: quarks themselves can't exist isolated in nature, they must be inside a meson or baryon. In fact, they usually produce jets of such particles.

  • Electrons are much lighter than quarks, and of course, mesons. To produce an electron-positron pair, you need a photon with at least 1.022 MeV, while the production of a pion pair needs a photon of around 300 MeV.


There are experiments of pion pair productions both in scattering of one photon and one proton [1] and scattering of two photons [2].


[1] M. Ripani et al.: Pion-pair production on a proton by photons in the energy region of nucleon-resonance excitation. (Link, behind paywall)


[2] A. E. Blinov et al.: Pion pair production in photon-photon collisions. (Link, behind paywall)


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