Update to the RHIC Letter of Intent for an experiment on particle and jet production at midrapidity

This document is an Update to the Letter of Intent (LOI) submitted by this collaboration in September 1990 proposing a large acceptance solenoidal tracking experiment. Since that time the collaboration has chosen the name STAR, representing Solenoidal Tracker At RHIC. The physics interests of the STAR collaboration and the goals of the experiment are described in the original LOI. Since submission of the LOI, several changes have been made in the design of the experiment motivated by the desire to expand pseudorapidity coverage for complete event characterization and by the necessity to achieve cost reduction. The major changes are: Expansion of pseudorapidity coverage to |η| < 4.5 by the addition of tracking chambers external to the magnet; reduction in the number of time-of-flight channels from 100K to 10K; staging implementation of hadronic calorimetry while using tracking and electromagnetic calorimetry to extract parton physics in the initial configuration; reduction in the cost per channel of Time Projection Chamber (TPC) electronics through continued TPC electronics R ampersand D supported from RHIC funds; and a change in the Silicon Vertex Tracker (SVT) technique to the use of silicon drift chambers. These changes and the status of ongoing R ampersand D programs to optimize the design and performance of the STAR experiment will be presented. In terms of detector performance it will be demonstrated that the space charge loading of the TPC is negligible and that the STAR experiment can operate at the highest RHIC luminosities. A summary of the detector systems is presented in this paper