Like many people, I've been chasing down idle curiosity, trying to get a better understanding of how certain particles interact with each other.

I have been particularly unsuccessful in trying to pin down what happens when an anti-down quark and an electron collide. Many of the other interactions I've looked into have (relatively...) simple answers such as "Nothing special happens," or "they annihilate," but I've been unable to even find that during my searching.

Have there been any experiments that examine collision between an anti-down quark and an electron?

This question is related to Are there different kinds of antimatter reactions? and Does a particle annihilate only with its antiparticle? If yes, why? but neither question addresses electron-quark interaction.


1 Answer 1


One possibility is that an electron and an anti-down quark simply scatter off each other. Another possibility is that the electron turns into an electron neutrino and the anti-down quark turns into an anti-up quark. With lower probability, other processes are possible in which more than two particles emerge.

They don’t annihilate because they aren’t antiparticles of each other. Annihilation into photons would not conserve electric charge, among other things.

I spent a few minutes looking for experiments studying collisions of electrons and antiprotons (which contain anti-down quarks) but didn’t find any.

Scattering of electrons from up and down quarks in protons and neutrons is well-studied, initially at SLAC in the late 1960’s.

As @probably_someone mentioned in a comment, there are virtual anti-down quarks in a proton, so some electrons colliding with a proton can be thought of as colliding with such an anti-down quark. This means that $ep$ scattering experiments presumably do test what you are asking about.

The antiparticle version of your question is well-studied with real (non-virtual) particles. For example, this paper discusses positron-proton collisions. Positrons are the antiparticles of electrons, and protons have down quarks inside.

[I’m] trying to get a better understanding of how certain particles interact with each other.

If you are interested in the possible interactions allowed by the Standard Model, this diagram from the Wikipedia article will be of interest. Unfortunately, it doesn’t include interactions involving Higgs bosons.

enter image description here

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    $\begingroup$ I suppose it would be easier to find positron-baryon collision experiments than electron-antibaryon experiments. Any of those? $\endgroup$ Sep 28, 2020 at 17:20
  • $\begingroup$ I’m shocked that I can’t easily find a diagram on the internet with all possible Standard Model vertices. Does anyone know of one? $\endgroup$
    – G. Smith
    Sep 28, 2020 at 17:42
  • $\begingroup$ @JohnDvorak I added a paragraph about that. $\endgroup$
    – G. Smith
    Sep 28, 2020 at 17:42
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    $\begingroup$ There are anti-down sea quarks in the proton, so presumably some small fraction of $ep$ collisions in deep inelastic scattering experiments will be between an electron and an anti-down sea quark. $\endgroup$ Sep 28, 2020 at 17:43

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