Comprehensive analysis of anomalous ANITA events disfavors a diffuse tau-neutrino flux origin

Abstract

Recently, the ANITA collaboration reported on two upward-going extensive air shower events consistent with a primary particle that emerges from the surface of the Antarctic ice sheet. These events may be of ντ origin, in which the neutrino interacts within the Earth to produce a τ lepton that emerges from the Earth, decays in the atmosphere, and initiates an extensive air shower. In this paper we estimate an upper bound on the ANITA acceptance to a diffuse ντ flux detected via τ -lepton-induced air showers within the bounds of Standard Model uncertainties. By comparing this estimate with the acceptance of Pierre Auger Observatory and IceCube and assuming Standard Model interactions, we conclude that a ντ origin of these events would imply a neutrino flux at least two orders of magnitude above current bounds.

Anomalous ANITA air shower events and tau decays

“…Standard model tau neutrino fluxes cannot be responsible for the ANITA unusual events as diffuse tau neutrino fluxes at this level are already excluded by IceCube [3] and Auger [10], as has already been emphasized recently by Romero-Wolf et al in Ref. [26]. IceCube and Auger set upper bounds on the diffuse tau neutrino differential flux (assuming equal fluxes neutrino flavors) in the range of E 2 ν Φ(E ν ) ∼ 10 −8 − 10 −7 GeV/cm 2 s sr for E ν = 10 8 − 10 10 GeV.…”

“…As the altitude at which a tau shower begins is increased, first the electric field gets larger, but after ∼ 6 km, the angle between the shower axis and line of sight (θ view in ref. [26]) decreases [26].…”

“…The ANITA effective aperture AΩ depends on the viewable area of the Earth below the detector and on the probability to observe a tau decay induced air shower at a given angle and altitude. The geometry is illus- [26]. The signals considered here come from air showers along the trajectory of an emerging tau that makes an angle θ tr with respect to the local normaln at its point of emergence from the Earth, which is at a co-latitude θ E relative to the line from the center of the Earth to ANITA.…”

“…The probability P obs that a tau neutrino with energy E ντ produces a shower that is detectable is [26,50]…”

“…Additionally, the first run of ANITA in 2016 run produced event 3985267, of shower energy of (0.6 ± 0.4) × 10 9 GeV, which emerged at an azimuthal elevation angle of −27.4 • ± 0.3 • , roughly 63 • from the zenith [18]. The interpretation of these unusual events as coming from tau neutrinos is problematic [18,19,26] because of the energies of the showers and the apparent angles of the tau neutrinos that induced them.…”