The Highest-Energy Cosmic Rays

Abstract

The search for the origin of cosmic rays with energies above 1018 eV has made considerable progress during the past few years. With new data from the High Resolution Fly's Eye experiment in Utah and the Pierre Auger Observatory in Argentina, a suppression of the cosmic ray flux above 5 × 1019 eV consistent with the predicted suppression arising from interaction with the cosmic microwave background (the so-called GZK suppression) has been observed. Recent results from Auger seem to indicate that the arrival direction distribution of cosmic rays with energies above the GZK suppression is not isotropic. Progress toward a better understanding of the chemical composition of the cosmic rays is under way. A new generation of detectors is providing data of unprecedented quality and quantity. In this article, we review these recent developments and briefly outline how our view of the highest-energy cosmic rays has evolved over the past several years.

New sensitivity to solar WIMP annihilation using low-energy neutrinos

“…Our calculated results are comparable to simply assuming that ∼ 10% of the annihilation energy goes into producing pions, i.e., N π ∼ 0.1 (2m χ /m π ). This is similar to the fraction of energy in hadronic showers in ultra-high-energy cosmic ray interactions in Earth's atmosphere [17]; the details differ, but the common element is that the dominant charged-pion loss process is hadronic scattering.For low-energy neutrinos, the rate and spectrum are very similar for nearly all final states, unlike the case for high-energy neutrinos. Quarks, gluons, weak bosons, and tau leptons all decay dominantly into hadrons, which produce pions.…”

“…Our calculated results are comparable to simply assuming that ∼ 10% of the annihilation energy goes into producing pions, i.e., N π ∼ 0.1 (2m χ /m π ). This is similar to the fraction of energy in hadronic showers in ultra-high-energy cosmic ray interactions in Earth's atmosphere [17]; the details differ, but the common element is that the dominant charged-pion loss process is hadronic scattering.…”

A Search for Ultra-High Energy Neutrinos and Cosmic-Rays with ANITA-2

“…This ], and provides the inal charge evolution e in radiation amplione in Ref. [18] (see also Fig. 14 below).…”

“…3: ANITA-1 limits based on no surviving candidates for 18 days of livetime. Other limits are from AMANDA [16], RICE [17], ANITA-lite [8], Auger [18], HiRes [20], FORTE [19]. The BZ (GZK) neutrino model range is determined by a variety of models [11,21,23,25,26,27,29].…”

“…18. A cut on the likelihood value of −2LL = 30, corresponding to a pointing σ ∼ 5.5, is used for event clustering.…”