The space--time structure of hadron production in high-energy collisions

Abstract: In this thesis, the space--time picture of the hadronization model has been implemented in the event generator Pythia. From this implementation, the hadronic behaviour has been studied for different scenarios, in order to begin addressing the unexpected collective behaviour of high-multiplicity pp events, which is typical for heavy-ion collisions. First, the temporal and radial evolution of pp and toy qqbar systems are analysed, illustrating the general motion of hadrons in the two systems. Then, the hadronic density is studied in the central region of the collisions, showing the presence of hadronic close-packing. This issue is further approached by tackling the hadronic density for different multiplicities, where pp collisions with higher multiplicity exhibit more significant close-packing than low-multiplicity collisions. It turns out, however, that colour reconnection gives a larger transverse area over which particle production occurs, and thereby a lesser density than without it. Finally, the hadronic overlap is studied as a function of transverse momentum for each newly generated hadron and for different multiplicities, illustrating that, although the importance of close-packing increases with multiplicity, it mainly affects low-pT hadrons.