News from Cosmic Ray Air Showers (ICRC 2019 -- Cosmic Ray Indirect Rapport)

Abstract

This rapport summarizes the cosmic-ray indirect (CRI) session of the 36 th ICRC conference. Updated measurements from several air-shower arrays with higher precision were shown leading to the discovery of new features in the energy spectrum: HAWC measures a softening of the light component (p+He) around 10 13.5 eV; measurements of the Pierre Auger Observatory show that the second knee is a smooth feature extending at least over the range of 100 − 200 PeV and that the energy spectrum between the ankle and the cut-off cannot be described by a simple broken power law. Measurements of the mass composition confirm that the composition is a varying mixture of protons and nuclei at least up to several 10 EeV. Hadronic interaction models constitute a significant uncertainty in the interpretation of measurements, but a joint effort of several collaborations helps to better assess their deficiencies, e.g., by quantifying the muon deficit in the models over the shower energy. Still, general trends in the average mass composition over energy are consistent for all state-of-the-art models. Anisotropy measurements with higher precision generally confirm earlier results, too. A change of the amplitude and phase of the equatorial dipole provides another indication that in the energy range between the second knee and the ankle there likely is a transition from Galactic to extragalactic sources. However, neither the most energetic Galatic nor the extragalactic sources have been discovered, yet, which remains a primary science goal of the field. Next to more exposure, an increase of measurement accuracy and decrease of systematic uncertainties will provide future progress. Therefore, it is particularly exciting that new experiments are built and existing experiments upgraded to increase the accuracy for the measurement of the energy and mass composition, e.g., by combining radio antennas with particle detectors. Last but not least, there is a trend that experiments are designed such that they can target cosmic rays, photons, and neutrinos at the same time, which will facilitate multi-messenger astrophysics at the highest energies.

Improved constraints on parton distributions using LHCb, ALICE and HERA heavy-flavour measurements and implications for the predictions for prompt atmospheric-neutrino fluxes

“…Each of the first five panels refers to a different CR primary all-nucleon spectrum (GST-3, GST-4, H3a, H3p[60,61], and Broken-Power-Law (BPL)[53], respectively), chosen among those most widely used in literature. In the lower bottom panel on the right-hand side the central predictions using all these primary all-nucleon spectra are compared among each other, and with those obtained with the more recently introduced Nijmegen[72] and Global Spline Fit (GSF)[73,74] all-nucleon spectra. At the highest E ν lab , the largest predictions (GST-4 and BPL) are seven time larger than the smallest one (H3a).…”

Advancing the Landscape of Multimessenger Science in the Next Decade

“…For instance, a possible selection-effect on the accelerated CRs at a SNR shock-front [504] was only detectable based on the AMS-02 spectra but not from direct observations of SNRs via photons. Further, composition-measurements of CRs around 10 15 eV might point to a different spectral behaviour of protons and heavier nuclei [505], a finding that needs to be further explored by direct CR-measurements for instance by Tibet ASγ [506], LHAASO [507] and SWGO [508], deeper observations in the electromagnetic spectrum of SNRs and theoretical models that are able to accommodate all these findings.…”