Evolution of the cosmic ray anisotropy above 10^{14} eV

M. Aglietta, V. V. Alekseenko, B. Alessandro, P. Antonioli, F. Arneodo, L. Bergamasco, M. Bertaina, R. Bonino, A. Castellina, A. Chiavassa, B. D'Ettorre Piazzoli, G. Di Sciascio, W. Fulgione, P. Galeotti, P. L. Ghia, M. Iacovacci, G. Mannocchi, C. Morello, G. Navarra, O. Saavedra, A. Stamerra, G. C. Trinchero, S. Valchierotti, P. Vallania, S. Vernetto, C. Vigorito

Published 2009-01-18Version 1

The amplitude and phase of the cosmic ray anisotropy are well established experimentally between 10^{11} eV and 10^{14} eV. The study of their evolution into the energy region 10^{14}-10^{16} eV can provide a significant tool for the understanding of the steepening ("knee") of the primary spectrum. In this letter we extend the EAS-TOP measurement performed at E_0 around 10^{14} eV, to higher energies by using the full data set (8 years of data taking). Results derived at about 10^{14} and 4x10^{14} eV are compared and discussed. Hints of increasing amplitude and change of phase above 10^{14} eV are reported. The significance of the observation for the understanding of cosmic ray propagation is discussed.