Main mechanism for the production of a higgs boson in Large Hadron Collider is the gluon fusion that is two of the gluons binding these protons collide and those energetic gluons form virtual top or bottom quark loop, which then decay into a higgs boson. I want to know how gluons form these virtual top or bottom quark loop. I know the Feynmann diagrams for the creation of those loops but I do not understand those diagrams. UCould you tell me, step by step, how gluons form virtual top or bottom quark loop.
Feynman diagrams are a shorthand for integrals entering a calculation for the crossection of a specific reaction, in your question the generation of the Higgs. When one writes the Feynman diagrams for the crossection of generating a Higgs in a proton proton interaction one must include all possible diagrams that obey the quantum number consrvations for the process. Therefore the "How" is answered by "all possible virtual processes have a probability for a given energy of proton proton scattering to generate an on mass shell higgs".
Now because the coupling of the higgs to the quarks is proportional to the mass of the quarks, the heavier quarks will enter the sum of Feynman diagrams with much larger probability than the lighter quarks.