News from Cosmic Ray Air Showers (ICRC 2019 — Cosmic Ray Indirect Rapport). (arXiv:1910.03721v1 [astro-ph.HE])

News from Cosmic Ray Air Showers (ICRC 2019 — Cosmic Ray Indirect Rapport). (arXiv:1910.03721v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Schroder_F/0/1/0/all/0/1">Frank G. Schr&#xf6;der</a>

This rapport summarizes the cosmic-ray indirect (CRI) session of the 36th
ICRC conference. Updated measurements from several air-shower arrays with
higher precision lead 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. A joint effort of several collaborations helps to better assess
deficiencies of hadronic interaction models, e.g., by quantifying the muon
deficit in the models over the shower energy. Anisotropy measurements with
higher precision generally confirm earlier results. A change of the amplitude
and phase of the equatorial dipole indicates 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, which remains a primary science
goal. Next to more exposure, an increase of measurement accuracy and decrease
of systematic uncertainties will provide future progress. It is particularly
exciting that new experiments are built and existing experiments upgraded to
increase the measurement accuracy 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.

This rapport summarizes the cosmic-ray indirect (CRI) session of the 36th
ICRC conference. Updated measurements from several air-shower arrays with
higher precision lead 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. A joint effort of several collaborations helps to better assess
deficiencies of hadronic interaction models, e.g., by quantifying the muon
deficit in the models over the shower energy. Anisotropy measurements with
higher precision generally confirm earlier results. A change of the amplitude
and phase of the equatorial dipole indicates 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, which remains a primary science
goal. Next to more exposure, an increase of measurement accuracy and decrease
of systematic uncertainties will provide future progress. It is particularly
exciting that new experiments are built and existing experiments upgraded to
increase the measurement accuracy 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.

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