There are several options under study which would allow integration of the second arm into the PHENIX
construction project. In order to have access to the detector systems of the first muon arm and of
the central arms, the central magnet must be moved along the beam direction toward arm 2. With the
shield wall removed, complete disassembly of the detector can then be accomplished by moving the
central magnet and attached detector systems laterally away from the beam line. To preserve this
access the second muon arm must be somewhat shorter than the first. A solution which appears
promising is to shorten the second arm by 1.5 m as is depicted in Fig. 1. This requires arm 2 to be
movable along the beam line. Because the magnetic lever arm is less there will be a degradation in the
mass resolution if the angular range of the second arm is identical to the first. PISA simulations
indicate an increase in the width of the from 
MeV for arm 1 to 
for arm 2. Alternately the second arm could have a piston structure with more iron, resulting in a
larger field and improved mass resolution. For
example, an increase in the inner angle from
to
, would result in a field integral comparable to the first arm, with a consequent
small loss of acceptance.. The most physics-effective way to strike this compromise (and others) is under
active study.