Cosmic Ray Sun Shadow in Soudan 2 Underground Muon Flux

TL;DR

This study reports the first measurement of the solar cosmic ray shadow using underground muon flux over a decade, revealing significant variation and a notable shadow during 1995-1998 influenced by the interplanetary magnetic field.

Contribution

It provides the first long-term measurement of the solar shadow in underground muons, linking shadow variations to solar magnetic activity.

Findings

Significant variation in the sun shadow over ten years.

A 3.3 sigma shadow observed during 1995-1998.

Shadow characteristics influenced by the interplanetary magnetic field.

Abstract

The absorption of cosmic rays by the sun produces a shadow at the earth. The angular offset and broadening of the shadow are determined by the magnitude and structure of the interplanetary magnetic field (IPMF) in the inner solar system. We report the first measurement of the solar cosmic ray shadow by detection of deep underground muon flux in observations made during the entire ten-year interval 1989 to 1998. The sun shadow varies significantly during this time, with a $3.3\sigma$ shadow observed during the years 1995 to 1998.