Non-perturbative models of diffractive hadronic collisions

In this thesis, a new model for diffractive proton-proton collisions is presented. Interpreting protons as systems of many partons, we treat diffraction in terms of elastic interactions between the partons of the colliding protons. Parton emission and absorption are employed as the mechanism that in the context of a diffractive event can stabilize excited protons by reshuffling parton momenta and dissipating the excess internal motion of the partons. The new model has been implemented in Herwig 7 and it reproduces observables commonly associated with diffractive physics. Additionally, it improves the description of several minimum-bias observables, especially the final state charged particle multiplicity distribution compared to the pre-existing Herwig 7 model for diffraction.
The last century has seen some extraordinary developments in our understanding of the quantum world. With the success of quantum electrodynamics, the first quantum field theory, the popularity of particle physics rose. Subsequently, a large number of scientists have been working on developing what is known as the standard model of particle physics. In the process, other quantum field theories including quantum chromodynamics, which describes the interactions of the elementary particles known as quarks and gluons, were formulated. The properties of particles can be experimentally probed by colliding them at very high energies, as is done at CERN in the Large Hadron Collider, the most powerful particle accelerator in the world, where protons are collided. Particle interactions can be very complex, especially for composite particles such as protons, which consist of quarks and gluons, collectively known as partons. In this regard, Monte Carlo event generators provide a way to compare theoretical predictions with observations. They are used to link various theoretical models together and predict the outcomes of experiments. All aspects of proton collisions have to be described and there are several kinds of interactions that protons can be involved in. Many are defined by the parts that can be described with the so-called perturbation theory and are well understood. There are other interactions, that are described using generally less reliable non-perturbative models and are therefore more problematic. These include what are known as diffractive events, which are defined and can be distinguished from other events by a large separation between regions where particles from either one or both protons breaking apart are detected. In the case of proton-proton collisions at the Large Hadron Collider diffractive events occur about 20% of the time. In my thesis, I introduce a new model with which diffractive processes are described as a set of simultaneous elastic collisions be