A comparison of the mass resolutions of the (North) PHENIX muon
tracking system and the occupancy of the tracking chambers with copper and BeO
nosecones, and the change in acceptances of 
vector meson muons will be presented. The
mass resolution of the vector meson would improve from 110 to 76 MeV, the
resolution would
improve from 135 to 98 Mev, and the 
resolution would improve from 200 to 177 MeV if a
beryllium oxide (BeO) nosecone were used in the North muon arm rather than a
copper nosecone. The acceptance in the North arm increases from
approximately 0.24% to 0.54%. However, the hit occupancy in the three tracking
stations in HIJET events increases from 20-30%, the number of tracks that pass
through at least 7 of 9 chambers increases by approximately 50%, and the number
of muons from 
and
K decay increases by approximately a factor of 1.75. The number of muons that
pass through the tracking stations and through at least 3 muon
identification planes, however, is similar for either the BeO nosecone or the
copper nosecone.