Silicon Vertex Tracker for PHENIX Upgrade at RHIC: Capabilities and   Detector Technology
  From the wealth of data obtained from the first three years of RHIC operation, the four RHIC experiments, BRAHMS, PHENIX, PHOBOS and STAR, have concluded that a high density partonic matter is formed at central Au+Au collisions at 200 GeV. The research focus now shifts from initial discovery to a detailed exploration of partonic matter. Particles carrying heavy flavor, i.e. charm or beauty quarks, are powerful tool for study the properties of the hot and dense medium created in high-energy nuclear collisions at RHIC. At the relatively low transverse momentum region, the collective motion of the heavy flavor will be a sensitive signal for the thermalization of light flavors. An upgrade of RHIC (RHIC-II) is intended for the second half of the decade, with a luminosity increase to about 20-40 times the design value of 8x1026 cm-2 s-1 for Au+Au, and 2x1032 cm-2 s-1 for polarized proton beams. The PHENIX collaboration plans to upgrade its experiment to exploit with an enhanced detector new physics then in reach. For this purpose, we are constructing the Silicon Vertex Tracker (VTX). The VTX detector will provide us the tool to measure new physics observables that are not accessible at the present RHIC or available only with very limited accuracy. The VTX detector consists of four layers of barrel detectors located in the region of pseudorapidity |eta| < 1.2 and covers almost 2 azimuthal angle. The pseudorapidity is defined as eta = -ln[tan(/2)], where is the emission angle relative to the beam axis. In this paper, we will provide details of the physics capability added to PHENIX by the new central silicon vertex tracker, the status of the project, including technology choices used in the design, performance of individual silicon sensor and silicon detector prototype. 
Rachid Nouicer (for the PHENIX Collaboration)