STAR inner tracking upgrade—a performance study

Abstract

Anisotropic flow measurements have demonstrated development of partonic collectivity in 200 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 p T region. Measurement of open charm spectra to high p T 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 p T 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 p T range will be demonstrated on v 2 (p T>0.5 GeV/c) and R CP (p T<10 GeV/c) measurements of D0 meson. Results of reconstruction of ΛC baryon in heavy-ion collisions are presented.