Reweighting-based analysis procedures and PMT gain calibrations in KM3NeT

With the advent of percent-level precision neutrino oscillation measurements, a detailed and precise understanding of systematic uncertainties in neutrino oscillation experiments is becoming increasingly important.
This thesis presents a new method which has been developed to study the impact of such uncertainties on results obtained by KM3NeT-ORCA, the part of the Cubic Kilometre Neutrino Telescope (KM3NeT) collaboration which aims to answer the question which of the known neutrinos is the lightest, by measuring matter effects in atmospheric neutrino oscillations.
The developed method comprises a collection of software tools and applications, which can be used to reweight simulations according to any data which are stored as part of the simulated event record.
Furthermore, it provides a variety of statistical tests with which the reweighted simulations can be compared with a given reference dataset.
The flexible set-up of the software allows a large variety of systematic uncertainties to be studied, which are otherwise more difficult to investigate.
Two case-studies are presented in this thesis, one for potential biases in the visible energies of simulated hadronic showers and one for next-to-leading order electroweak corrections to neutrino scattering cross-sections.
In addition to the above, a new method is presented for calibrating the PMT gains in KM3NeT, based on a refined model of the PMT analogue pulses and a new high-voltage tuning procedure.
The effect of the first applications of the new calibration routines in the ORCA detector are shown.