Quark recombination

In case of cluster fragmentation models color-singlet clusters of partons form after the perturbative phase of jet development and then decay into the observed hadrons. The clusters originate from gluon splitting in quark pairs and subsequent recombination with neighboring quarks and antiquarks. Afterward, the clusters are assumed to decay isotropically in their rest frame into pairs of hadrons, where the branching ratios are determined by the density of states. 

The fundamental interaction is the electromagnetic scattering of the electron on a parton qi. The details of how the struck parton recombines with those partons that did not interact, so as to form physical hadrons, is not well understood. Since partons or quarks are assumed not to exist as real physical particles there must be unit probability for them to transmute into physical hadrons. 

We have seen in this section, that there occurred a short phase in the early universe when density and temperature was high enough for the fusion of hydrogen into heavier elements up to lithium and boron. Hydrogen (protons) was present since protons were formed form quark particles. Neutral hydrogen since the recombination age. However, the second constiment of water molecules, oxygen, was not formed dming these phases. In the next section we will describe the evolution of stars and see how elements heavier than lithium can be synthesized by thermonuclear fusion reactions inside stars. 

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