The STAR Heavy Flavor Tracker (HFT)

The heavy quark hadrons are suggested as a clean probe for studying the early dynamic evolution of the dense and hot medium created in high-energy nuclear collisions. The Heavy Flavor Tracker (HFT) of the STAR experiment, designed to improve the vertex resolution and extend the measurement capabilities in the heavy flavor domain, was installed for the 2014 heavy ion run of RHIC. It is composed of three different silicon detectors arranged in four concentric cylinders close to the STAR interaction point. The two innermost layers are based on CMOS monolithic active pixels (MAPS), featured for the first time in a collider experiment, and the two outer layers are based on pads and strips. The two innermost HFT layers are placed at a radius of 2.8 and 8~cm from the beam line and accommodate 400 ultra-thin (50μm) high resolution MAPS sensors arranged in 10-sensor ladders to cover a total silicon area of 0.16m2. Each sensor includes a pixel array of 928 rows and 960 columns with a 20.7μm pixel pitch, providing a sensitive area of ∼3.8cm2. The sensor features 185.6μs readout time and 170mW/cm2 power dissipation, allowing it to be air cooled, which results in a global material budget of only 0.5% radiation length per layer in the run 14 detector. A novel mechanical approach to detector insertion enables effective installation and integration of the pixel layers within a 12 hour shift during the on-going STAR Run. After a detailed description of the design specifications and the technology implementation, the detector status and operations during the 200 GeV Au+Au RHIC run of 2014 will be presented in this paper. A preliminary estimation of the detector performance meeting the design requirements will be reported.