Narrow muon bundles from muon pair production in rock

We revise the process of muon pair production by high-energy muons in rock using the recently published cross-section. The three-dimensional Monte Car lo code MUSIC has been used to obtain the characteristics of the muon bundl es initiated via this process. We have compared them with those of conventi onal muon bundles initiated in the atmosphere and shown that large undergro und detectors, capable of collecting hundreds of thousands of multiple muon events, can discriminate statistically muon induced bundles from conventio nal ones. However, we find that the enhancement of the measured muon decohe rence function over that predicted at small distances, recently reported by the MACRO experiment, cannot be explained by the effect of muon pair produ ction alone, unless its cross-section is underestimated by a factor of 3. ( C) 1999 Published by Elsevier Science B.V. All rights reserved.