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 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 × 10 19 eV. The principal conclusions are (1) The flattening of the spectrum near 5 × 10 18 eV, the so-called "ankle," is confirmed. (2) The steepening of the spectrum at around 5 × 10 19 eV is confirmed. (3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index γ of the particle flux (∝ E −γ) changes from 2.51 AE 0.03 ðstatÞ AE 0.05 ðsystÞ to 3.05 AE 0.05 ðstatÞ AE 0.10 ðsystÞ before changing sharply to 5.1 AE 0.3 ðstatÞ AE 0.1 ðsystÞ above 5 × 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 × 10 18 eV.

We report on the measurement of the ^{7}Be(n,p)^{7}Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a ^{7}Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal ^{7}Li(p,n)^{7}Be reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near-threshold neutron production in the p+^{7}Li reaction is also discussed.

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 index changes from Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

No 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.