Mapping the internal structure of hadrons through color and spin effects

Abstract

Originally it was thought that the proton is not divisible into smaller particles. However, from collision experiments it follows that it consists of a ‘soup’ of countless ‘colored’ elementary particles such as quarks and gluons that are kept together by the strong nuclear force. The particles constituting the proton are also referred to as partons and their distributions are described by parton distribution functions (PDFs). As these functions cannot be calculated, they must be extracted from experiment. More knowledge on PDFs teaches us more about the inner workings of protons and enables us to more accurately describe collisions between protons at the Large Hadron Collider (LHC). In this thesis we have studied quantities that depend on various types of PDFs. We have investigated one particular PDF called the Boer-Mulders function that describes correlations between the spin and transverse momentum of quarks inside the proton. This function gives rise to a very specific asymmetry in the directions of produced particles. In contrast to earlier expectations, we have shown that this PDF does not suffer from quantum effects related to color entanglement. Furthermore, we have introduced various new gluon PDFs that contain interesting information on the behavior of gluons. As it turns out, the description of the gluon content of particles such as protons simplifies tremendously in certain collisions at very high energies. Finally, we have derived how certain asymmetries that have been observed in collisions between protons and lead nuclei at the LHC can be related to quantum correlations between gluons