Narrow muon bundles from muon pair production in rock

TL;DR

This paper investigates muon pair production in rock and its impact on underground muon bundle characteristics, highlighting the potential for large detectors to distinguish muon-induced bundles from atmospheric ones, but also questioning previous experimental anomalies.

Contribution

It provides a revised analysis of muon pair production using updated cross-sections and assesses its significance in muon bundle observations in underground detectors.

Findings

Muon pair production can be statistically distinguished in large underground detectors.

The observed muon decoherence cannot be fully explained by muon pair production alone.

A potential underestimation of the cross-section by a factor of 3 could reconcile observations.

Abstract

We revise the process of muon pair production by high-energy muons in rock using the recently published cross-section. The three-dimensional Monte Carlo code MUSIC has been used to obtain the characteristics of the muon bundles initiated via this process. We have compared them with those of conventional muon bundles initiated in the atmosphere and shown that large underground detectors, capable of collecting hundreds of thousands of multiple muon events, can discriminate statistically muon induced bundles from conventional ones. However, we find that the enhancement of the measured muon decoherence function over that predicted at small distances, recently reported by the MACRO experiment, cannot be explained by the effect of muon pair production alone, unless its cross-section is underestimated by a factor of 3.