The Observation of a Shadow of the Moon in the Underground muon flux in the Soudan 2 detector

TL;DR

This paper reports the detection of the moon's shadow in underground muon flux using the Soudan 2 detector, confirming the detector's precise alignment and stability over ten years.

Contribution

First observation of the moon's shadow in underground muon flux at this depth, demonstrating the detector's high angular resolution and long-term stability.

Findings

Moon shadow observed with 5 sigma significance

Detector's angular resolution is less than 0.3 degrees

Alignment stability confirmed over ten years

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 a sigma of less than 0.3 degrees. The position of the shadow confirms that the alignment of the detector is known to better than 0.15 degrees and has remained stable during ten years of data taking.