Introduction

The PHENIX Muon Identifiers are shown in Figure 1. They consist of panels of Iarocci tubes arranged for hodoscopic read-out interleaved between steel plates which are all behind the Muon Tracking Magnets. There are five steel plates in each Muon Identifier arm as shown in the close-up of Figure 2. The gaps of the Muon Identifier are numbered 1 through 6 counting from the interaction vertex direction outwards. The first gap is between the return yoke of the Muon Magnet and the first identifier plate. The thicknesses of the steel plates are, counting outwards from the vertex, 10, 10, 20, 20, and 20 cm. The absorber material of the central magnet pole pieces and the return yokes are also integral parts of the Muon Identifiers. In both cases the central magnet poles are 60-cm thick. The thickness of the return yoke of the North Muon Magnet is 30 cm, and the thickness of the return yoke of the South Muon Magnet is 20 cm. The minimum energy thresholds for minimum ionizing particles which reach each plane of the Muon Identifier are tabulated in Table I.

Because of funding issues, it has been determined that the PHENIX experiment will only instrument five of the six available gaps in the Muon Identifier. The purpose of this note is to provide a look at the physics impact of not instrumenting the 6th gap of the Muon Identifier.

Figure 1: Side view of the PHENIX Detector. The North and South Muon Identifiers are shown behind the North and South Muon Magnets, respectively. Each Muon Identifier consists of 6 gaps between steel plates into which Iarocci tubes arranged for hodoscopic read out can be placed.

Figure 2: A close-up view of the beam pipe region of the North Muon Identifier. The Muon Identifier panels, which are Iarocci tubes arranged for x-x', and y-y' read-out are shown in red. The Muon Identifier steel plates are shown in gray. The gaps are numbered from 1 through 6, as shown. The South Muon Identifier is a mirror image of the North Muon Identifier. However, because of the shorter length of the South Muon Magnet, gap 1 is approximately 1.5-m long on the South Muon Identifier.