A conceptual design for the STAR endcap electromagnetic calorimeter

Abstract

In order to make measurements of the gluon spin or helicity distribution in the proton or the gluon spin average distribution in nuclei, both a barrel and an endcap electromagnetic calorimeter must be added to the STAR baseline detector. Information on the gluon will be obtained in inclusive direct-{gamma} + jet and jet + jet production. In order to be sensitive to the proper gluon kinematic regions, either the direct-{gamma} or the jet must be in the endcap electromagnetic calorimeter (EMC). However, the endcap EMC is not large enough to completely contain the jets, so that the barrel EMC is also needed. This note describes a conceptual design for the STAR endcap EMC. Constraints are imposed by the space available between the end of the time projection chamber (TPC) and the inside of the magnet pole tip iron. Severe constraints also occur near {vert_bar}{eta}{vert_bar} = 1, where the barrel and endcap EMC`s meet. Cables from detectors inside the EMC, including those from the TPC, will exit from STAR near {vert_bar}{eta}{vert_bar} = 1. The constraints in this region have not yet been seriously studied since no decision on the detailed routing of these cables was available at the time this work was being done. This report includes details of the conceptual design, analytical and finite element calculations of stresses in various structural members for the endcap EMC, and a preliminary cost estimate.