A schematic of the North arm of the PHENIX muon tracking system
is shown in Figure 1. At the front of the magnet, it is proposed to have a 28
cm thick "nosecone" which will absorb pions and kaons before they can decay to
muons and produce copious background muons in the tracking system. The muon
baseline has a nosecone which is made of copper material. It has been proposed
that a nosecone of a possibly more optimum material beryllium oxide, BeO, could
possibly be used instead of copper. BeO, while not providing the same number
of interaction lengths to absorb the hadrons, would still provide absorption of
hadrons, while causing less energy straggling for muons which are incident from
the vertex. This paper will show the improved performance of mass resolutions
that would be expected for the 
, J/
and 
vector mesons with the BeO nosecone as compared to a
copper nosecone, as well as the changes in chamber occupancies and number of
full tracks that pass through the spectrometer and reach the third muon
identification plane.
Figure 1: One arm of the PHENIX muon tracking system, showing the magnet and the three tracking stations, followed by muon identifier planes.