Le Coultre, P (reprint author), Univ Geneva, CH-1211 Geneva, Switzerland.
The shadowing of high-energy cosmic rays by the Moon has been observed with a significance of 9.4 standard deviations with the L3 + C muon spectrometer at CERN. A significant effect of the Earth magnetic field is observed. Since no event deficit on the east side of the Moon has been observed, an upper limit at 90% confidence level on the antiproton to proton ratio of 0.11 is obtained for primary energies around 1 TeV. (c) 2005 Elsevier B.V. All rights reserved.