It Is Possible to Create Protons from Photons?

YesThis is possible from colliding real photons (i.e., on-shell photons).

Protons (p) are composite particles composed of three quarks: two up quarks (u) of charge +2/3 e and one down quark (d) of charge 1/3 e. While, anti-protons (p¯) consist of two up antiquarks (u¯) of charge 2/3 e and one down antiquark (d¯) of charge +1/3 e. So, in principle, production of pp¯ is allowed in γγ (gamma gamma) collisions. 

This can be understand by the following Feynman diagram :

The quark-quark-photon and antiquark-antiquark-photon vertices in the above diagram can be understood using electromagnetic interactions such as QED. The process will lead to the formation of a pp¯ pair if the initial collision γγ  has enough energy to produce a proton-antiproton pair. Three quarks (two u quarks and one d quark) and three antiquarks (two u¯ antiquarks and one d¯ antiquark) are needed for this. As a result, we need Feynman's diagrammatic expansion:


According to the allowed vertices in electroweak and QCD theories (in the Standard Model of elementary particles), the dashed part of this diagram contains an infinite number of terms . There are three vertices in QCD. One of the simplest Feynman diagrams is as follows:

or

It's worth noting that the four possible vertices are applied, as follows:



We now have three quarks (q) and three antiquarks (q¯). Supposing that two of quarks are u quarks and one of them is d quark, and supposing that two of antiquarks are u¯ antiquarks and one of them is d¯ antiquark. 

The three quarks hadronized into proton, and the three antiquarks hadronized into anti-proton in the end. In a number of studies, this process has been confirmed experimentally and analysed. In conclusion, photons can be used to make protons (together with anti-protons).






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