Monte Carlo Simulations for BSM Physics
and Precision Higgs Physics at the LHC

Abstract

Monte Carlo event generators are indispensable tools for the interpretation of data taken
at particle collider experiments like the Large Hadron Collider (LHC), the most powerful
particle collider to date. In this thesis, the general purpose Monte Carlo event generator
Sherpa is used to implement a new simulation framework for models that go beyond the
Standard Model of particle physics. This is achieved by means of an newly designed interface
to a universal format for generic models and by extending existing functionalities in such a
way as to handle a generic class of coupling structures that appear in many extensions of
the Standard Model. Furthermore, an improved modeling of the dominant LHC Higgs pro-
duction mechanism in the Standard Model is described and the effects of the improvements
are quantified. The improved simulation that is implemented in Sherpa supplements the
description of Higgs production at the LHC in terms of an effective Higgs-gluon interaction
with finite top quark mass effects that restore a reliable description of the kinematics in
events with large momentum transfers. Using this improved description of Higgs production
at the LHC, this work demonstrates how the transverse momentum spectrum of the Higgs
boson can be used to constrain models that modify the Higgs-gluon coupling. In addition,
state-of-the-art Monte Carlo event generation techniques are used in order to assess the
sensitivity of analysis strategies in the search for invisibly decaying Higgs bosons. In this
analysis, it was found that previously neglected loop-induced contributions have a significant
impact and it is demonstrated how multi-jet merging techniques can be used to obtain a
reliable description of these contributions. Furthermore, the work presented in the last
chapter of this thesis shows how jet substructure techniques can be used in order to search
for rare Higgs decays into light resonances that decay further into hadrons. This analysis
closes with a demonstration on how such an analysis can be used to constrain extensions of
the Standard Model that feature multiple Higgs bosons.