Observation of the Moon Shadow in Deep Underground Muon Flux

Abstract

A shadow of the moon, with a statistical significance of $5\sigma$, has been observed in the underground muon flux at a depth of 2090 mwe using the Soudan 2 detector. The angular resolution of the detector is well described by a Gaussian with $\sigma \le 0.3^{\circ }$. The position of the shadow confirms the alignment of the detector to better than $0.15^{\circ }$. This alignment has remained stable during 10 years of data taking from 1989 through 1998.