Simulation study on the optical processes at deep-sea neutrino telescope sites

The performance of a large-scale water Cherenkov neutrino telescope relies heavily on the transparency of the surrounding water, quantified by its level of light absorption and scattering. A pathfinder experiment was carried out to measure the optical properties of deep seawater in South China Sea with light-emitting diodes (LEDs) as light sources, photon multiplier tubes (PMTs) and cameras as photon sensors. Here, we present an optical simulation program employing the Geant4 toolkit to understand the absorption and scattering processes in the deep seawater, which helps to extract the underlying optical properties from the experimental data. The simulation results are compared with the experimental data and show good agreements. We also verify the analysis methods that utilize various observables of the PMTs and the cameras with this simulation program, which can be easily adapted by other neutrino telescope pathfinder experiments and future large-scale detectors.Comment: 27 pages, 11 figure

Posteriori analysis on IceCube double pulse tau neutrino candidates

The IceCube Neutrino Observatory at the South Pole detects Cherenkov light emitted by charged secondary particles created by primary neutrino interactions. Double pulse waveforms can arise from charged current interactions of astrophysical tau neutrinos with nucleons in the ice and the subsequent decay of tau leptons. The previous 8-year tau double pulse analysis found three tau neutrino candidate events. Among them, the most promising one observed in 2014 is located very near the dust layer in the middle of the detector. A posterior analysis on this event will be presented in this paper, using a new ice model treatment with continuously varying nuisance parameters to do the targeted Monte Carlo re-simulation for tau and other background neutrino ensembles. The impact of different ice models on the expected signal and background statistics will also be discussed

The Performance of Double Cascades Identification in IceCube-Gen2

The IceCube Neutrino Observatory is a cubic-kilometer in-ice Cherenkov detector located at the South Pole. At high energies, the neutrino flux of is expected to be observed in the ratio of 1 : 1 : 1 on Earth. A ternary particle identification technique on the basis of three event topologies,single cascades, double cascades, and tracks, has been developed. While tracks arise mainly from charged-current muon neutrino interactions, single cascades from neutral-current interactions of all neutrino flavors and many charge-current interactions of electron neutrinos. Double cascades arise from charged-current tau neutrino interactions and its subsequent non-muonic decay of the taus if the decay length is large enough to be resolved. Such double cascades are unique to tau neutrinos and can be used to identify them. The next-generation neutrino observatory, IceCube-Gen2 will have an instrumented volume nearly 10 times greater than IceCube and a different geometry with larger string spacing. In this thesis, evaluation on the performance of double cascades identification in IceCube-Gen2 is realized by analyzing the IceCube high-energy starting event sample but only using a subset of the optical sensors that is similar in layout to the future IceCube-Gen2 geometry