The cosmic ray spectrum above 4 EeV as measured with inclined showers recorded at the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION (AUTOR 434 DE 474); M. TUEROS (COAUTOR)

Beijing

Conferencia; The 32nd International Cosmic Ray Conference; 2011

Institute of High Energy Physics, Chinese Academy of Sciences

The energy spectrum above 4×1018 eV is presented, obtained from 5936 events with zenith angles exceeding 62◦ collected by the Surface Detector of the Pierre Auger Observatory from 1 January 2004 to 31 December 2010. Showers with such large zenith angles are muon-dominated at ground level and the radial symmetry around the shower axis is broken due to geomagnetic deflections. They are analysed separately from showers with smaller zenith angles using two-dimensional models of the muon density at ground, allowing one to reconstruct a global muon number for every event. The conversion of the muon number to energy is obtained using the sub-sample of events detected simultaneously with both the Surface and the Fluorescence Detector. The spectrum obtained displays suppression near 4 × 1019 eV compatible with the analysis that uses less inclined events.