Detailed investigations of PMTs in optical sensors for neutrino telescopes such as IceCube Upgrade

Photomultiplier tubes (PMTs) are a central component of neutrino telescopes such as IceCube and KM3NeT, and an accurate understanding and measurement of their properties is indispensable for improvements of these experiments. In this contribution we focus on a detailed investigation of the photocathode and the dynode system and their influence on the performance of the PMT. Three methods are used for the investigation. Ellipsometry measurements of the photocathode analyze its optical properties in terms of absorption probability and refractive index. Scans of the photocathode in single photon illumination probe performance differences along the photocathode surface. Systematic deviations in the resulting amplifications are compared to electric field and electron tracing simulations through the dynode system to understand the measured values. The goal is an extensive understanding of efficiency, amplification, and timing as functions of wavelength and impact point as well as angle.Comment: Presented at the 38th International Cosmic Ray Conference (ICRC2023). See arXiv:2307.13047 for all IceCube contribution

Sensitivity of multi-PMT Optical Modules in Antarctic Ice to Supernova Neutrinos of MeV energy

New optical sensors with a segmented photosensitive area are being developed for the next generation of neutrino telescopes at the South Pole. In addition to increasing sensitivity to high-energy astrophysical neutrinos, we show that this will also lead to a significant improvement in sensitivity to MeV neutrinos, such as those produced in core-collapse supernovae (CCSN). These low-energy neutrinos can provide a detailed picture of the events after stellar core collapse, testing our understanding of these violent explosions. We present studies on the event-based detection of MeV neutrinos with a segmented sensor and, for the first time, the potential of a corresponding detector in the deep ice at the South Pole for the detection of extra-galactic CCSN. We find that exploiting temporal coincidences between signals in different photocathode segments, a $27\ \mathrm{M}_{\odot}$ progenitor mass CCSN can be detected up to a distance of 341 kpc with a false detection rate of $0.01$ year$^{-1}$ with a detector consisting of 10000 sensors. Increasing the number of sensors to 20000 and reducing the optical background by a factor of 70 expands the range such that a CCSN detection rate of $0.1$ per year is achieved, while keeping the false detection rate at $0.01$ year$^{-1}$.Comment: Published versio

Hybrid cosmic ray measurements using the IceAct telescopes in coincidence with the IceCube and IceTop detectors

IceAct is a proposed surface array of compact (50 cm diameter) and cost-effective Imaging Air Cherenkov Telescopes installed at the site of the IceCube Neutrino Observatory at the geographic South Pole. Since January 2019, two IceAct telescope demonstrators, featuring 61 silicon photomultiplier (SiPM) pixels have been taking data in the center of the IceTop surface array during the austral winter. We present the first analysis of hybrid cosmic ray events detected by the IceAct imaging air-Cherenkov telescopes in coincidence with the IceCube Neutrino Observatory, including the IceTop surface array and the IceCube in-ice array. By featuring an energy threshold of about 10 TeV and a wide field-of-view, the IceAct telescopes show promising capabilities of improving current cosmic ray composition studies: measuring the Cherenkov light emissions in the atmosphere adds new information about the shower development not accessible with the current detectors, enabling significantly better primary particle type discrimination on a statistical basis. The hybrid measurement also allows for detailed feasibility studies of detector cross-calibration and of cosmic ray veto capabilities for neutrino analyses. We present the performance of the telescopes, the results from the analysis of two years of data, and an outlook of a hybrid simulation for a future telescope array