Because the muons from 
decay have low momentum, many of decay muons are absorbed by the
copper nosecone or reduced in momentum enough that they can not reach the third
plane of the muon identification system (a requirement for triggering on a
muon), thus reducing the acceptance of s into the spectrometer. This, plus the geometric
acceptance causes the overall acceptance of 's to be approximately 0.24% in the muon arm
if a copper nosecone is used. If the BeO nosecone is used, the overall
acceptance increases to 0.54%. In the South arm, because the nosecone is
shorter and the theta angle acceptance is different, the acceptance changes
from approximately 0.3% to 0.36%.