STAR inner tracking upgrade - A performance study

Abstract

Anisotropic flow measurements have demonstrated development of partonic collectivity in $200\mathrm{GeV}$ Au+Au collisions at RHIC. To understand the partonic EOS, thermalization must be addressed. Collective motion of heavy-flavor (c,b) quarks can be used to indicate the degree of thermalization of the light-flavor quarks (u,d,s). Measurement of heavy-flavor quark collectivity requires direct reconstruction of heavy-flavor hadrons in the low $\pt$ region. Measurement of open charm spectra to high $\pt$ can be used to investigate heavy-quark energy loss and medium properties. The Heavy Flavor Tracker (HFT), a proposed upgrade to the STAR experiment at midrapidity, will measure $v_{2}$ of open-charm hadrons to very low $\pt$ by reconstructing their displaced decay vertices. The innermost part of the HFT is the PIXEL detector (made of two low mass monolithic active pixel sensor layers), which delivers a high precision position measurement close to the collision vertex. The Intermediate Silicon Tracker (IST), a 1-layer strip detector, is essential to improve hit identification in the PIXEL detector when running at full RHIC-II luminosity. Using a full GEANT simulation, open charm measurement capabilities of STAR with the HFT will be shown. Its performance in a broad $\pt$ range will be demonstrated on $v_{2}$ ($\pt > 0.5\mathrm{GeV}/c$) and $R_\mathrm{CP}$ ($\pt < 10\mathrm{GeV}/c$) measurements of $\D$ meson. Results of reconstruction of $\Lc$ baryon in heavy-ion collisions are presented.