Delayed light emission to distinguish astrophysical neutrino flavors in IceCube
August 16, 2017
August 03, 2018
IceCube, a cubic kilometer Cherenkov detector, is an ideal instrument for the detection of astrophysical neutrino fluxes and rare interactions of exotic particles. One way to advance IceCube neutrino analyses would be the development of methods to identify the neutrino flavor and reaction type. While charged current interactions leading to long tracks of charged muons can be easily distinguished from those leading to particle cascades of O(10) m extension, the 17 m sensor distance makes it very challenging to identify the type of cascade as being due to the fragmentation of the struck nucleus or due to showers initiated by electrons or tauons. Only at very high energies, the average tau flight distance of 50 m/PeV, in principle, allows one to identify a tau-neutrino interaction. So far, IceCube has not registered telltale events of such kind. The creation of neutrons, spallation products and muons in hadronic showers offers an alternative handle to identify a hadronic interaction. However, the regular data acquisition system is restricted to a O(10) microsecond readout window, limiting the detection to relativistic or low relativistic particles. Recently, the development of a spooling system to store the complete detector hit map for a configurable time interval made it possible to register a potential "afterglow" of highly energetic events. While the signal from Michel electrons from muon decay will be difficult to extract due to light scattering in the ice and afterpulses of the PMTs, the detection of 2.224 MeV photons from neutron capture on hydrogen is promising due to the low PMT dark rates of the sensors in IceCube. One should note that luminescence in the ice could be a competing effect. In this paper, we summarize the physics scope and particle identification opportunities, study the underlying physics of delayed signals and the expected detector response in a Cherenkov detector, discuss a newly installed automatic real time triggering system, with emphasis on the the capabilities and limitations of the data acquisition system for such an analysis, and outline the expected potential of IceCube for particle identification through the use of delayed signals.
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