The STAR collaboration is preparing a challenging tracking detector upgrade program to further investigate fundamental properties of the new state of strongly interacting matter produced in relativistic-heavy ion collisions at RHIC and to provide fundamental studies of the nucleon spin structure and dynamics in high-energy polarized proton-proton collisions at RHIC.
A key step in this direction is the ability for the direct reconstruction of charm and beauty decays as well as flavor tagged jets to allow a precise measurement of the spectra, yields and flow of open charm and beauty production. The measurement of the nuclear modification factor RAA from central to peripheral collisions is a critical step for particles containing heavy quarks. This will allow fundamental tests of QCD predictions of heavy quark energy loss.
The measurement of heavy quark (charm/beauty) production in polarized proton-proton collisions would allow an extension of the capabilities to measure the gluon contribution to the proton spin in particular towards lower values of the gluon momentum fraction. The measurement of heavy quark production in gluon-gluon initiated processes, gg ! Q¯Q, would provide a stringent test of the underlying Standard Model dynamics for both unpolarized and polarized measurements.
The reconstruction of open charm and beauty production requires a precision micro-vertex detector and intermediate tracking detector capable of directly observing charm and beauty decays. This is the focus of the Heavy Flavor Tracker (HFT), a high-resolution micro-vertex detector based on active pixel sensor (APS) technology in combination with a new Intermediate Silicon Tracker (IST). The reconstruction of open charm and beauty production in proton-proton collisions and for low multiplicity events in relativistic heavy-ion collisions in particular, requires a new intermediate tracking system together with the existing STAR silicon-strip detector (SSD) and the STAR Time-Projection Chamber (TPC).
This new silicon barrel detector, the Intermediate-Silicon Tracker (IST), is expected to replace the current STAR Silicon Vertex Tracker (SVT) which is based on silicon drift detectors. The IST would establish a track-pointing device for the HFT, connecting TPC tracks to the high-precision inner HFT layers. The design is chosen in such a way to provide independent tracking capabilities based on the IST for beauty production at a center-of-mass energy of 500GeV in polarized proton-proton collisions. The anticipated design of the IST will be compatible with the STAR Data Acquisition Upgrade (DAQ1000). A combination of well-established silicon strip sensors and silicon pad sensors is foreseen for the IST design. It should be stressed that the integrated tracking upgrade for STAR based on well-established, intrinsically fast detector and readout elements, will provide a significant improvement of the existing STAR tracking system, in particular for the expected high luminosity operation at RHIC. The proposed design will allow to have tracking information available at the trigger level. This will aid the selection of rare events already at the trigger level. Bates was responsible for the design, fabrication, testing and installation of the Intermediate Silicon Tracker as well as maintenance during it’s lifetime.
