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The LHC is a proton-proton collider. If I wanted to draw a leading order Feynman diagram for a two-quark production in proton-proton collisions, would it be correct to draw sth like this, or would this be forbidden due to flavour violation at the vertex (for example one $u$-quark and $d$-quark would annihilate to a gluon)?

enter image description here

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    $\begingroup$ How is this “two-quark production”? You’ve got two before and two after. $\endgroup$
    – G. Smith
    Commented Jan 4, 2021 at 1:12
  • $\begingroup$ @G.Smith we would call this dijet production (if you draw a bar over two of the qs). It's a fair thing to be interested in. However I would prefer if OP consulted even the most basic reference before posting. $\endgroup$
    – kaylimekay
    Commented Jan 4, 2021 at 4:46
  • $\begingroup$ thomasgmccarthy.com/an-introduction-to-collider-physics-iii might be a useful introduction $\endgroup$
    – Nihar Karve
    Commented Jan 4, 2021 at 7:20

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If I assume that your diagram is to be read from left to right, then it seems that two quarks respectively coming from the two colliding protons, annihilate. However, for quarks to annihilate, one needs to be an anti-quark. So what one would expect instead is a gluon exchange between the two quarks with enough energy to try and kick the quarks out of the protons. Then, because of the strength of the strong force and the effects of confinement it would generate additional quarks.

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This is a comment for education.

In this link, antiproton proton scattering explicitly shows how when dealing with composite particles one has to keep track of what the whole does, before and after, in order to have a correct interaction quantum numbers and all.

antopp

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