Study of event shape observables and jet production in pp collisions generated by PYTHIA 8 at √s =14 TeV

Abstract

In this thesis we discuss event shapes of simulated pp collisions as generated by PYTHIA 8, a program for high-energy particle collision simulations developed by Lund University, based on the Monte-Carlo method. We analyze two sets of simulated events (one minimum bias, one with hard only hard QCD processes at ˆpT ,min = 20GeV) by calculating a triplet of event shapes: transverse sphericity, spherocity and 3-dimensional sphericity, the correlations between them, and how they perform for different cuts in multiplicity and pseudorapidity η. Subsequently, we will use FastJet3 to find jets in these events and analyze how the existence of one or multiple jets affects performance of the different event shape observables. We conclude that for events with hard QCD processes, all event shape observables are reasonable indicators of jets in an event. Transverse sphericity and spherocity struggle with events with large spread in η, which 3-dimensional sphericity does account for. For minimum bias events, none of the event shape observables are trustworthy indicators of jets in an event, nor the other way around, unless all low-multiplicity events are omitted from the dataset, in which case the performance of all event shape observables is improved significantly.