We review open questions and prospects for progress in ultrahigh-energy cosmic ray
(UHECR) research, based on a series of discussions that took place during the “The High …

In this report we review the important progress made in recent years towards understanding
the experimental data on ultra-high-energy (E≳ 1 0 9 GeV) cosmic rays. We begin with a …

We report a measurement of the energy spectrum of cosmic rays for energies above 2.5× 10
18 eV based on 215,030 events recorded with zenith angles below 60°. A key feature of the …

We report a measurement of the energy spectrum of cosmic rays above 2.5× 10 18 eV
based on 215 030 events. New results are presented: at about 1.3× 10 19 eV, the spectral …

We report a study of the distributions of the depth of maximum, X max, of extensive air-
shower profiles with energies above 1 0 17.8 eV as observed with the fluorescence …

Abstract The Pierre Auger Observatory, located on a vast, high plain in western Argentina, is
the world׳ s largest cosmic ray observatory. The objectives of the Observatory are to probe …

The Pierre Auger Observatory has begun a major Upgrade of its already impressive
capabilities, with an emphasis on improved mass composition determination using the …

The sharp change in slope of the ultrahigh energy cosmic ray (UHECR) spectrum around 1
0 18.6 eV (the ankle), combined with evidence of a light but extragalactic component near …

We present the first measurement of the fluctuations in the number of muons in extensive air
showers produced by ultrahigh energy cosmic rays. We find that the measured fluctuations …

A search for ultra-high energy photons with energies above 1EeV is performed using nine
years of data collected by the Pierre Auger Observatory in hybrid operation mode. An …