Evidence for suppression of the flux of cosmic rays above 4x10^19 eV

PIERRE AUGER COLLABORATION (J. ABRAHAM, ... , A. MARIAZZI, ET AL)

PHYSICAL REVIEW LETTERS

The American Physical Society (APS)

Año: 2007

0031-9007

A measurement of the energy spectrum of cosmic rays above 2.5 x 1018 eV with the Pierre Auger Observatory based on about 20000 events with zenith angle less than 60o is described. The spectral index γ  of the particle flux , J α E-γ   , at energies between   4 x 1018 eV and 4 x 1019 eV  is 2.69 0.02(stat) 0.06 (syst) becoming 4.2 0.4(stat)  0.06(syst) at higher energies. The hypothesis of a single power-law is rejected with a significance greater than 6 standard deviations. Taken together with the recent report that cosmic rays above 5.7 x  1019 eV are of extragalactic  orign, it is possible that the steepening of the spectrum predicted by Greisen, Zatsepin and Kus´min has been observed.