Comparing the plots for the total (inelastic) cross sections as a function of the centre of mass energy for $pp$ and $e^+e^-$ collisions:

proton-proton cross section

electron-positron cross section

one notes that the trend at high energy is opposite: the $pp$ cross section increases while the $e^+e^-$ decreases. Is there a (simple) explanation for this?

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    $\begingroup$ Note that the electron cross-section, away from resonances, seems to be proportional to $1/\sqrt E$ (if center-of-mass energy $E$ is what's on that unlabeled horizontal axis). Also note that the e-e plot would fit only in the left half of the hadron plot, so maybe stuff starts happening again at higher energy. I don't know, though. $\endgroup$ – rob Jan 29 '16 at 0:01
  • $\begingroup$ @rob Yes, that's obviously energy [GeV], as easily inferred from the masses of the resonances. Regarding the stuff happening at higher energy: one expects resonances at the Higgs and at the Top masses, but there are no hints that the general trend should be altered. $\endgroup$ – DarioP Jan 29 '16 at 7:51
  • $\begingroup$ There's probably a simple interpretation for the $1/\sqrt E$ cross section in e-e. Thermal (milli-eV) neutrons have the same shape, and the usual explanation is that the cross section is proportional to inverse of the speed, or to the "dwell time" near a nucleus (but of course that particular argument doesn't hold for relativistic electrons). If you can predict the $1/\sqrt E$ cross section for electrons you should find yourself making an assumption that is broken for protons. $\endgroup$ – rob Jan 29 '16 at 19:13

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