Abstract
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 inner-most layers are based on CMOS monolithic active pixels (MAPS), featured for the first time in a collider experiment, while the two outer layers are based on pads and strips. The two innermost HFT layers are placed at a radius of 2.7 and 8 cm from the beam line and accommodate 400 ultra-thin (50 μm) high resolution MAPS sensors arranged in 10-sensor ladders to cover a total silicon area of 0.16 m2. Each sensor includes a pixel array of 928 rows and 960 columns with a 20.7 μm pixel pitch, providing a sensitive area of ∼ 3.8 cm2. The sensor features 185.6 μs readout time and 170 mW/cm2 power dissipation. The detector is air-cooled, allowing a global material budget as low as 0.39% X/X0 on the inner layer. A novel mechanical approach to detector insertion enables effective installation and integration of the pixel layers within an 8 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 current 200 GeV Au+Au run will be presented in this paper, with a particular focus on calibration and general system operations aimed at stabilizing the running conditions. A preliminary estimation of the detector performance meeting the design requirements will be reported.
Highlights
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
Heavy quark measurements are a key component of the heavy ion program for the systematic characterization of the dense medium created in heavy ion collisions, the so-called Quark-Gluon Plasma (QGP) [1]
The outermost layer is placed at 22 cm from the beam line and is equipped with the Silicon Strip Detector (SSD): it is based on double sided silicon strip sensors with 95 μm interstrip pitch and 35 mrad relative P- N-side stereo angle inclination; the SSD silicon and front-end chips come from an existing detector and have been equipped with new faster electronics
Summary
One of the main goals of the STAR experiment at the relativistic Heavy Ion Collider (RHIC) at the 2Ban0rd0ooAGkhueaV+vAefonurNcAoalt+liioAsnioaanlnsLdaaubt posretavoteorr√aylsise=ntoer5sgt0ui0edsyGupep+Vptof,odr√+psA+u=p, collisions with the aim to reproduce and characterize. The Heavy Flavor Tracker (HFT) has been designed to extend the STAR measurement capabilities in the heavy flavor domain [2] It consists of 4 cylindrical layers of silicon detectors inserted inside the TPC inner field cage. The sensor chip used for the PXL detector is the Ultimate-2 MAPS sensor developed by IPHC in Strasbourg, France, and optimized for the STAR environment These sensors use pixels with a pitch of 20.7 μm arranged in a 928 (rows) by 960 (columns) array (a total of 890k pixels per sensor) on a 20.22 mm × 22.71 mm chip with a high-resistivity epitaxial layer for increased radiation hardness and improved signal-to-noise performance. Configuration by the JTAG protocol allows the control of many internal parameters
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