Nuclear modifications in strange particle production in proton-lead collisions at the LHC

Abstract

Identified particle spectra provide an important tool for understanding the particle production mechanism and the dynamical evolution of the quark-gluon plasma (QGP) created in relativistic heavy ion collisions. Studies involving strange and multi-strange hadrons carry additional information since there is no net strangeness content in the initial colliding system. In smaller collisions systems, such as proton-proton (pp) or proton-lead (pPb) collisions it was expected that QGP will not be formed, due to the small volume. However some recent observations of collective effects in high-multiplicity pp and pPb collisions have led to a paradigm shift. This thesis examines the question of QGP formation and particle production mechanisms in pp, pPb and PbPb collisions using strange and multi-strange hadrons detected in the CMS experiment over a broad kinematic range. The spectral shapes and particle ratios are compared in the different collision systems for events that have the same multiplicity and interpreted in the context of hydrodynamics models. Nuclear modification factors are measured out to high transverse momentum in minimum bias pPb collisions in several rapidity regions with the goal of investigating possible modifications in hard-scattering processes using identified hadrons. Forward-backward rapidity yield asymmetries are also studied as a function of transverse momentum to search for initial-state effects, such as shadowing in the nuclear parton distributions.