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Register a new userCosmic tau neutrino detection via Cherenkov signals from air showers from Earth-emerging taus
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We perform a new, detailed calculation of the flux and energy spectrum of Earth-emerging $tau$-leptons generated from the interactions of tau neutrinos and antineutrinos in the Earth. A layered model of the Earth is used to describe the variable density profile of the Earth. Different assumptions regarding the neutrino charged- and neutral-current cross sections as well as the $tau$-lepton energy loss models are used to quantify the systematic uncertainty from these on the results. A baseline simulation is then used to generate the optical Cherenkov signal from upward-moving extensive air showers generated by the $tau$-lepton decay in the atmosphere, applicable to a range of space-based instruments. We use this simulation to determine the neutrino sensitivity for $E_ u>$ 10 PeV for a space-based experiment with performance similar to that for the Probe of Extreme MultiMessenger Astrophysics (POEMMA) mission currently under study.
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We estimate the rate of observable Horizontal and Upward Tau Air-Showers (HORTAUs, UPTAUS) considering both the Earth opacity and the finite size of the terrestrial atmosphere. We calculate the effective target volumes and masses for Tau air-showers emerging from the Earth. The resulting model-independent masses for satellite experiments such as EUSO may encompass at E_nu_tau = 10^19 eV a very large volume, V= 1020 km^3. Adopting simple power law neutrino fluxes, E^-2 and E^-1, calibrated to GZK-like and Z-Burst-like models, we estimate that at E= 10^19 eV nearly half a dozen horizontal shower events should be detected by EUSO in three years of data collection by the guaranteed GZK neutrino flux. We also find that the equivalent mass for an Earth outer layer made of rock is dominant compared to the water, contrary to simplified all-rock/all-water Earth models and previous Montecarlo simulations. Therefore we expect an enhancement of neutrino detection along continental shelves nearby the highest mountain chains, also given the better geometrical acceptance for Earth skimming neutrinos. The Auger experiment might reveal such a signature at E_nu= 10^{18} eV (with 26 events in 3 yr) towards the Andes, if the angular resolution at the horizon (both in azimuth and zenith) would reach an accuracy of nearly one degree needed to disentangle tau air showers from common UHECR. The number of events increases at lower energies; therefore we suggest an extension of the EUSO and Auger sensitivity down to (or even below) E_nu = 10^19 eV and E_nu = 10^18 eV respectively.
We have detected Cherenkov light from air showers with Geiger-mode APDs (G-APDs). G-APDs are novel semiconductor photon-detectors, which offer several advantages compared to conventional photomultiplier tubes in the field of ground-based gamma-ray astronomy. In a field test with the MAGIC telescope we have tested the efficiency of a G-APD / light catcher setup to detect Cherenkov light from air showers. We estimate a detection efficiency, which is 60% higher than the efficiency of a MAGIC camera pixel. Ambient temperature dark count rates of the tested G-APDs are below the rates of the night sky light background. According to these recent tests G-APDs promise a major progress in ground-based gamma-ray astronomy.
Future experiments based on the observation of Earths atmosphere from sub-orbital and orbital altitudes plan to include optical Cherenkov cameras to observe extensive air showers produced by high-energy cosmic radiation via its interaction with both the Earth and its atmosphere. As discussed elsewhere, particularly relevant is the case of upward-moving showers initiated by astrophysical neutrinos skimming and interacting in the Earth. The Cherenkov cameras, by looking above Earths limb, can also detect cosmic rays with energies starting from less than a PeV up to the highest energies (tens of EeV). Using a customized computation scheme to determine the expected optical Cherenkov signal from these high-energy cosmic rays, we estimate the sensitivity and event rate for balloon-borne and satellite-based instruments, focusing our analysis on the Extreme Universe Space Observatory aboard a Super Pressure Balloon 2 (EUSO-SPB2) and the Probe of Extreme Multi-Messenger Astrophysics (POEMMA) experiments. We find the expected event rates to be larger than hundreds of events per hour of experimental live time, enabling a promising overall test of the Cherenkov detection technique from sub-orbital and orbital altitudes as well as a guaranteed signal that can be used for understanding the response of the instrument.
The first detection of high-energy astrophysical neutrinos by IceCube provides new opportunities for tests of neutrino properties. The long baseline through the Cosmic Neutrino Background (C$ u$B) is particularly useful for directly testing secret neutrino interactions ($ u$SI) that would cause neutrino-neutrino elastic scattering at a larger rate than the usual weak interactions. We show that IceCube can provide competitive sensitivity to $ u$SI compared to other astrophysical and cosmological probes, which are complementary to laboratory tests. We study the spectral distortions caused by $ u$SI with a large s-channel contribution, which can lead to a dip, bump, or cutoff on an initially smooth spectrum. Consequently, $ u$SI may be an exotic solution for features seen in the IceCube energy spectrum. More conservatively, IceCube neutrino data could be used to set model-independent limits on $ u$SI. Our phenomenological estimates provide guidance for more detailed calculations, comparisons to data, and model building.
The possibilities of detecting high energy neutrinos through inclined showers produced in the atmosphere are addressed with an emphasis on the detection of air showers by arrays of particle detectors. Rates of inclined showers produced by both down-going neutrino interactions and by up-coming $tau$ decays from earth-skimming neutrinos as a function of shower energy are calculated with analytical methods using two sample neutrino fluxes with different spectral indices. The relative contributions from different flavors and charged, neutral current and resonant interactions are compared for down-going neutrinos interacting in the atmosphere. No detailed description of detectors is attempted but rough energy thresholds are implemented to establish the ranges of energies which are more suitable for neutrino detection through inclined showers. Down-going and up-coming rates are compared.
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