Abstract We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the ...spectrum is observed, confirming the presence of the so-called second-knee feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented ...precision. By using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between $$2\times 10^{17}$$ 2×1017 and $$2\times 10^{18}$$ 2×1018 eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger than those predicted by models. We quantify this discrepancy by combining the measurements from the muon detector with those from the Auger fluorescence detector at $$10^{{17.5}}\, {\mathrm{eV}} $$ 1017.5eV and $$10^{{18}}\, {\mathrm{eV}} $$ 1018eV . We find that, for the models to explain the data, an increase in the muon density of $$38\%$$ 38% $$\pm 4\% (12\%)$$ ±4%(12%) $$\pm {}^{21\%}_{18\%}$$ ±18%21% for EPOS-LHC, and of $$50\% (53\%)$$ 50%(53%) $$\pm 4\% (13\%)$$ ±4%(13%) $$\pm {}^{23\%}_{20\%}$$ ±20%23% for QGSJetII-04, is respectively needed.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ApJ 933 (2022) 125 Ultra-high-energy photons with energies exceeding $10^{17}$ eV offer a wealth
of connections to different aspects of cosmic-ray astrophysics as well as to
gamma-ray and neutrino ...astronomy. The recent observations of photons with
energies in the $10^{15}$ eV range further motivate searches for even
higher-energy photons. In this paper, we present a search for photons with
energies exceeding $2{\times}10^{17}$ eV using about 5.5 years of hybrid data
from the low-energy extensions of the Pierre Auger Observatory. The upper
limits on the integral photon flux derived here are the most stringent ones to
date in the energy region between $10^{17}$ and $10^{18}$ eV.
Eur. Phys. J. C (2021) 81:966 We present a measurement of the cosmic-ray spectrum above 100\,PeV using the
part of the surface detector of the Pierre Auger Observatory that has a spacing
of 750~m. An ...inflection of the spectrum is observed, confirming the presence of
the so-called \emph{second-knee} feature. The spectrum is then combined with
that of the 1500\,m array to produce a single measurement of the flux, linking
this spectral feature with the three additional breaks at the highest energies.
The combined spectrum, with an energy scale set calorimetrically via
fluorescence telescopes and using a single detector type, results in the most
statistically and systematically precise measurement of spectral breaks yet
obtained. These measurements are critical for furthering our understanding of
the highest energy cosmic rays.
JINST 16 P07019 (2021) The atmospheric depth of the air shower maximum $X_{\mathrm{max}}$ is an
observable commonly used for the determination of the nuclear mass composition
of ultra-high energy ...cosmic rays. Direct measurements of $X_{\mathrm{max}}$ are
performed using observations of the longitudinal shower development with
fluorescence telescopes. At the same time, several methods have been proposed
for an indirect estimation of $X_{\mathrm{max}}$ from the characteristics of
the shower particles registered with surface detector arrays. In this paper, we
present a deep neural network (DNN) for the estimation of $X_{\mathrm{max}}$.
The reconstruction relies on the signals induced by shower particles in the
ground based water-Cherenkov detectors of the Pierre Auger Observatory. The
network architecture features recurrent long short-term memory layers to
process the temporal structure of signals and hexagonal convolutions to exploit
the symmetry of the surface detector array. We evaluate the performance of the
network using air showers simulated with three different hadronic interaction
models. Thereafter, we account for long-term detector effects and calibrate the
reconstructed $X_{\mathrm{max}}$ using fluorescence measurements. Finally, we
show that the event-by-event resolution in the reconstruction of the shower
maximum improves with increasing shower energy and reaches less than
$25~\mathrm{g/cm^{2}}$ at energies above $2\times 10^{19}~\mathrm{eV}$.
Phys. Rev. D 102, 062005 (2020) We report a measurement of the energy spectrum of cosmic rays for energies
above $2.5 {\times} 10^{18}~$eV based on 215,030 events recorded with zenith
angles below ...$60^\circ$. A key feature of the work is that the estimates of the
energies are independent of assumptions about the unknown hadronic physics or
of the primary mass composition. The measurement is the most precise made
hitherto with the accumulated exposure being so large that the measurements of
the flux are dominated by systematic uncertainties except at energies above $5
{\times} 10^{19}~$eV. The principal conclusions are: (1) The flattening of the
spectrum near $5 {\times} 10^{18}~$eV, the so-called "ankle", is confirmed. (2)
The steepening of the spectrum at around $5 {\times} 10^{19}~$eV is confirmed.
(3) A new feature has been identified in the spectrum: in the region above the
ankle the spectral index $\gamma$ of the particle flux ($\propto E^{-\gamma}$)
changes from $2.51 \pm 0.03~{\rm (stat.)} \pm 0.05~{\rm (sys.)}$ to $3.05 \pm
0.05~{\rm (stat.)} \pm 0.10~{\rm (sys.)}$ before changing sharply to $5.1 \pm
0.3~{\rm (stat.)} \pm 0.1~{\rm (sys.)}$ above $5 {\times} 10^{19}~$eV. (4) No
evidence for any dependence of the spectrum on declination has been found other
than a mild excess from the Southern Hemisphere that is consistent with the
anisotropy observed above $8 {\times} 10^{18}~$eV.
Phys. Rev. Lett. 125, 121106 (2020) We report a measurement of the energy spectrum of cosmic rays above
$2.5{\times} 10^{18}$ eV based on $215,030$ events. New results are presented:
at about ...$1.3{\times} 10^{19}$ eV, the spectral index changes from $2.51 \pm
0.03 \textrm{ (stat.)} \pm 0.05 \textrm{ (sys.)}$ to $3.05 \pm 0.05 \textrm{
(stat.)}\pm 0.10\textrm{ (sys.)}$, evolving to $5.1\pm0.3\textrm{ (stat.)} \pm
0.1\textrm{ (sys.)}$ beyond $5{\times} 10^{19}$ eV, while no significant
dependence of spectral features on the declination is seen in the accessible
range. These features of the spectrum can be reproduced in models with
energy-dependent mass composition. The energy density in cosmic rays above
$5{\times} 10^{18}$ eV is $(5.66 \pm 0.03 \textrm{ (stat.)} \pm 1.40 \textrm{
(sys.)} ) {\times} 10^{53}~$erg Mpc$^{-3}$.
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