Probing the origin of ultra-high-energy cosmic rays with neutrinos in the EeV energy range using the Pierre Auger Observatory

Abstract

Neutrinos with energies above 1017 eV are detectable with the Surface Detector Array of the Pierre Auger Observatory. The identification is efficiently performed for neutrinos of all flavors interacting in the atmosphere at large zenith angles, as well as for Earth-skimming τ neutrinos with nearly tangential trajectories relative to the Earth. No neutrino candidates were found in ∼ 14.7 years of data taken up to 31 August 2018. This leads to restrictive upper bounds on their flux. The 90% C.L. single-flavor limit to the diffuse flux of ultra-high-energy neutrinos with an Eν−2 spectrum in the energy range 1.0 × 1017 eV –2.5 × 1019 eV is E2 dNν/dEν < 4.4 × 10−9 GeV cm−2 s−1 sr−1, placing strong constraints on several models of neutrino production at EeV energies and on the properties of the sources of ultra-high-energy cosmic rays.

Askaryan radiation from neutrino-induced showers in ice

“…The vector potential obtained in ZHAireS simulations is compared to that obtained using the approximation in Eq. (19) with agreement again at the few percent level. As can also be seen in Fig.…”

“…(d) For a τ produced in a ν τ CC interaction and decaying hadronically one can obtain the vector potential with Eq. (19). If the τ decays in an electron, Eq.…”

“…The latter are designed to detect the radiation in the MHz-GHz frequency range generated in ν-induced showers from the excess charge that develops in showers, first discussed by Askaryan in 1962 [18]. Despite all of these efforts neutrinos have escaped detection in the EeV energy range by existing experiments using these techniques [19][20][21][22]. About three orders of magnitude in energy below, in the 100 TeV to PeV range, the IceCube experiment has detected with high confidence a flux of astrophysical neutrinos [7,8], including evidence of an energetic neutrino from a direction consistent with blazar TXS 0506+056 in temporal coincidence with a flaring state [23].…”

Observing EeV neutrinos through Earth: GZK and the anomalous ANITA events

“…for Earth-skimming neutrinos, where the probability of detecting a tau in the atmosphere after a single neutrino interaction in the Earth is optimized [20][21][22][23][24][25][26][27][28]. Here, we show how using the secondary flux will extend this search to the entire sky.…”

“…Similarly, neutrino detectors sensitive to higher energies compared to IceCube have typically limited searches to Earth-skimming or downgoing trajectories, where the column depth is optimal for detecting EHE neutrinos after a single interaction [20]. Experiments such as ANITA, ARA, ARIANNA, and the Pierre Auger Observatory have set limits on the cosmogenic flux taking advantage of the Earth-skimming technique [21][22][23][24][25][26][27][28].…”