Improving the Super-Kamiokande 20-inch PMT modelling using the photosensor test facility (PTF)




Gousy-Leblanc, Vincent

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The Super-Kamiokande (Super-K) experiment is a water Cerenkov neutrino experiment in Japan that won a Nobel prize for discovering neutrino oscillation in 1998. Since then, the neutrino mixing angles and the mass squared differences were measured by various experiments. However, after over 20 years of measurements, some neutrino parameters remain unknown: the nature of neutrino: Dirac or Majorana, the $\theta_{23}$ octant degeneracy,$\delta_{cp}$, the mass hierarchy and the absolute mass of neutrinos. To perform these measurements, larger statistics are required along with a reduction of systematic uncertainties. The first issue will be resolved by next-generation neutrino experiments such as Hyper-Kamiokande and Deep Underground Neutrino Experiment (DUNE ) experiment, which will have unprecedented fiducial volumes. The second issue is more complicated to solve because systematic uncertainties can come from a variety of sources: the interaction model used for neutrino interactions, the geometry of the detector, detector response, water purity etc.\\ The first part of this thesis will discuss the recommissioning, improvement and measurement of a Super-K photomultiplier tube (PMT) response at the photosensor test facility (PTF) at the TRI-University Meson Facility (TRIUMF) laboratory. This facility can replicate the conditions in Super-K (ultra-pure water and low magnetic field) and allows control of external parameters (magnetic field, incident position and angle of light as well as its polarization and wavelength) to study their effect on the PMT response. The second part will discuss the integration of these measurements into the Monte Carlo simulations to estimate the uncertainty related to the detector response. A biased study with a 1GeV muon in the vertical and horizontal direction showed a 1.95$\%$ difference in the total charge (sum of the charge collected by the PMT) between the modified and nominal simulation. The reconstructed momentum had a similar difference of 1.88$\%$. This study demonstrates that the position dependence of the PMT response has an impact on the reconstruction of physics quantities. It is a first step to better understand the detector response and characterize the systematic uncertainty of the Super-K detector.



particle physics, calibration detector, detector simulation, water Cerenkov experiment, signal processing, photosensors, neutrino, Super-Kamiokande