We report on an upward traveling, radio-detected cosmic-ray-like impulsive event with characteristics closely matching an extensive air shower. This event, observed in the third flight of the ...Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload, is consistent with a similar event reported in a previous flight. These events could be produced by the atmospheric decay of an upward-propagating τ lepton produced by a ν_{τ} interaction, although their relatively steep arrival angles create tension with the standard model neutrino cross section. Each of the two events have a posteriori background estimates of ≲10^{-2} events. If these are generated by τ-lepton decay, then either the charged-current ν_{τ} cross section is suppressed at EeV energies, or the events arise at moments when the peak flux of a transient neutrino source was much larger than the typical expected cosmogenic background neutrinos.
The ANtarctic Impulsive Transient Antenna (ANITA) NASA long-duration balloon payload completed its fourth flight in December 2016, after 28 days of flight time. ANITA is sensitive to impulsive ...broadband radio emission from interactions of ultrahigh-energy neutrinos in polar ice (Askaryan emission). We present the results of two separate blind analyses searching for signals from Askaryan emission in the data from the fourth flight of ANITA. The more sensitive analysis, with a better expected limit, has a background estimate of 0.64−0.45+0.69 and an analysis efficiency of 82±2%. The second analysis has a background estimate of 0.34−0.16+0.66 and an analysis efficiency of 71±6%. Each analysis found one event in the signal region, consistent with the background estimate for each analysis. The resulting limit further tightens the constraints on the diffuse flux of ultrahigh-energy neutrinos at energies above 1019.5 eV.
The Antarctic Impulsive Transient Antenna, a NASA long-duration balloon payload, searches for radio emission from interactions of ultrahigh-energy neutrinos in polar ice. The third flight of the ...Antarctic Impulsive Transient Antenna was launched in December 2014 and completed a 22-day flight. We present the results of three analyses searching for Askaryan radio emission of neutrino origin. In the most sensitive of the analyses, we find one event in the signal region on an expected background of 0.7−0.3+0.5. Though consistent with the background estimate, the event remains compatible with a neutrino hypothesis even after additional postunblinding scrutiny.
We report on four radio-detected cosmic-ray (CR) or CR-like events observed with the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload. Two of the four ...were previously identified as stratospheric CR air showers during the ANITA-I flight. A third stratospheric CR was detected during the ANITA-II flight. Here, we report on characteristics of these three unusual CR events, which develop nearly horizontally, 20-30 km above the surface of Earth. In addition, we report on a fourth steeply upward-pointing ANITA-I CR-like radio event which has characteristics consistent with a primary that emerged from the surface of the ice. This suggests a possible τ-lepton decay as the origin of this event, but such an interpretation would require significant suppression of the standard model τ-neutrino cross section.
Strongly interacting matter in the form of nuggets of nuclear-density material is not currently excluded as a dark matter candidate in the ten gram to hundreds of kilogram mass range. A recent ...variation on quark nugget dark matter models postulates that a first-order imbalance between matter and antimatter at the quark-gluon phase transition in the early Universe could lead to most of the dark matter bound into heavy (baryon number B∼1025) antiquark nuggets in the current epoch, explaining both the dark matter preponderance and the matter-antimatter asymmetry. Interactions of these massive objects with normal matter in the Earth and Sun lead to annihilation and an associated neutrino flux in the ∼30 MeV range. We calculate these fluxes for antiquark nuggets of sufficient flux to account for the dark matter and find that current neutrino flux limits from Super-Kamiokande (SuperK) exclude these objects as major dark matter candidates at a high confidence level. Antiquark nuggets in the previously allowed mass range cannot account for more than ∼15% of the dark matter flux.
We report results from 120 h of live time with the Goldstone lunar ultrahigh energy neutrino experiment (GLUE). The experiment searches for < or = 10 ns microwave pulses from the lunar regolith, ...appearing in coincidence at two large radio telescopes separated by 22 km and linked by optical fiber. Such pulses would arise from subsurface electromagnetic cascades induced by interactions of > or = 100 EeV (1 EeV = 10(18) eV neutrinos in the lunar regolith. No candidates are yet seen, and the implied limits constrain several current models for ultrahigh energy neutrino fluxes.
ANITA's fourth long-duration balloon flight in 2016 detected 29 cosmic-ray (CR)-like events on a background of 0.37_{-0.17}^{+0.27} anthropogenic events. CRs are mainly seen in reflection off the ...Antarctic ice sheets, creating a phase-inverted waveform polarity. However, four of the below-horizon CR-like events show anomalous noninverted polarity, a p=5.3×10^{-4} chance if due to background. All anomalous events are from locations near the horizon; ANITA-IV observed no steeply upcoming anomalous events similar to the two such events seen in prior flights.
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 ν τ 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 ν τ 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 ν τ origin of these events would imply a neutrino flux at least two orders of magnitude above current bounds.
We report new limits on cosmic neutrino fluxes from the test flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment, which completed an 18.4 day flight of a prototype long-duration ...balloon payload, called ANITA-lite, in early 2004. We search for impulsive events that could be associated with ultrahigh energy neutrino interactions in the ice and derive limits that constrain several models for ultrahigh energy neutrino fluxes and rule out the long-standing -burst model.
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