In this article we want to introduce the IceCube Neutrino Observatory. In a first part we focus on the input of KIT and DESY for the developments of SiPM-readout scintillation detectors for an extended surface array of IceCube and IceCube-Gen2.
IceCube is a unique detector, not only due to the discovery of very high energy cosmic neutrinos, but also as a multipurpose research facility. It also contributes to cosmic ray physics, dark matter searches and glaciology, and is therefore most suitable for multi-messenger astroparticle physics.
IceCube Neutrino Observatory
The IceCube Neutrino Observatory is located at the South Pole to observe the cosmos using optical modules deep in the ice and ice Cherenkov tanks at the surface (IceTop).
IceCube Lab at sunset
(Credit: Martin Wolf, IceCube/NSF)
With 5160 digital optical modules, deployed in a cubic kilometre of ancient ice at 1450 m to2450 m depth, this in-ice component measures Cherenkov light generated by neutrino induced particles in the TeV energy range. The optical modules are employed with a ten-inch photomultiplier and corresponding electronics. 60 optical modules form one string and in total 86 strings are deployed.
The DeepCore subdetector with denser configuration lowers the energy threshold to 10 GeV and allows the investigation of neutrino oscillations.
IceTop acts as a veto and calibration detector for IceCube and is additionally used as a cosmic ray particle detector in an energy range from 300 TeV to 1 EeV.
IceCube detector schematic
(Credit: IceCube Collaboration)
A collection of science highlights in the different fields can be found on: http://icecube.wisc.edu/science/highlights
Further information about the IceCube Neutrino Observatory is available at their website: http://icecube.wisc.edu/
Due to the excellent performance of the detector and the discovery of the astrophysical neutrinos the idea of a next-generation Neutrino Observatory was natural. The new IceCube-Gen2 collaboration is currently exploring the capabilities of such a detector.
(Credit: IceCube collaboration)
The future IceCube detector shall deliver statistically significant samples of very high energy astrophysical neutrinos, in the PeV to EeV range, and detect hundreds of neutrinos across all flavors at energies above 100 TeV. It includes the dense array PINGU, but also a radio enhancement like ARA is considered for detecting neutrinos above EeV. In addition, the in-ice instrumentation shall be complemented by a large-area surface component for veto issues and cosmic ray measurements.
IceCube-Gen2 is presented in more detail here: http://icecube.wisc.edu/science/beyond
At the moment several R&D projects are going on and in this article we focus on the work of KIT and DESY on a future scintillator surface array.
R&D at KIT and DESY for IceScint
An array of scintillation detectors can be used to increase the veto capabilities for cosmogenic neutrinos and enables an improvement in the reconstruction of cosmic-ray induced air-showers. The Institut für Kernphysik at KIT and the astroparticle group at DESY decided to build such a scintillator array combining the existing TAXI DAQ, developed by DESY, with newly developed scintillation detectors based on the knowledge gained at KIT by building also the upgrade of the Pierre Auger Observatory, AugerPrime.
The IceScint detector is made of Fermilab scintillator bars and wavelength shifting fibres readout by state-of-art silicon photomultipliers (SiPMs).
With the single photon calibration stand at KIT (SPOCK) the most suitable SiPM for scintillator readout was specified and before installation, the SiPM characteristics of each installed SiPM were measured. The 6x6mm² Hamamatsu S13360-6025PE was found to be best suited for the specific requirements. Below the Photon Detection Efficiency and the Gain as a function of the overvoltage for one of the installed SiPMs are shown:
For a first prototype detector several parts of the detector had to be developed, measured and tested for functionality in environmental conditions like at the South Pole. As example, a new analog readout module, consisting of three printed circuit boards, a new optical coupling and a modified routing of the optical fibers was developed. The performance of all prototype detectors was measured with an established calibration setup, the muon tower at KIT.
In close cooperation between KIT and DESY the interface between the analog readout and the TAXI DAQ was developed. The SiPM is first connected to an analog readout module that comprises: a cookie board with analog temperature sensor that houses the SMD-soldered SiPM; an adapter board designed for mechanical stability that allows the SiPM on the cookie board to be attached to the ends of the optical fibers coming out of the scintillator bars; a readout board that houses the SiPM power supply (Hamamatsu C11204-02) and three different pre-amplifiers (1x, 5x, 10x); and finally, a general purpose board that contains line drivers to transmit the analog signal from the scintillator panel to the Scintillator Field Hub (SFH) subsystem that includes data handling, power, and timing distribution between the IceCube Laboratory and each scintillator station. The IceTAXI DAQ is an FPGA plus ARM embedded Linux system.
Layout of the analog readout module
In the season 2017/18 one of these prototype stations was deployed at the South Pole by people from KIT, UW-Madison and DESY.
Impressions of detector deployment at the South Pole
The station comprises of seven scintillation detectors communicating with the SFH, where the TAXI DAQ is located. The alignment of the station is an array in hexagonal shape and approx. 60m side length, with the field hub in the middle. In January 2018 the station was deployed and first measurements were done that are very promising.
The next steps are to calibrate the detector station, creating an analysis framework, establishing a data stream with higher bandwidth and analyse the measured air shower events of the station showcasing technological advances for the next generation in cosmic-ray detection.
Pictures and Plots on "R&D at KIT and DESY for IceScint" by courtesy of Marie Oehler, Bernd Hofmann and Thomas Huber, text and pictures on "IceCube Observatory" from their website http://icecube.wisc.edu/