The HFT, a Stand-alone Heavy Flavor Tracker for STAR.

Alexandre Shabetai

Thermalization is a key factor in determining the partonic EoS of the medium produced in ultra-relativistic nuclear collisions. Elliptic flow (v2) measurements of multistrange baryons at RHIC have already suggested the development of collectivity among partons before hadronization. If heavy flavor hadrons flow with the light flavor hadrons, this indicates frequent interactions beween the light (u,d,s) and heavy (c,b) quarks. Thus, thermalization of light quarks is likely to have been reached through partonic re-scattering. Experimentally this can be verified by making a direct measurement of D-mesons v2 with sufficient precision at low transverse momentum. Using the Heavy Flavor Tracker (HFT) detector, the STAR experiment at RHIC, is proposing to both study this process, and also to directly reconstruct charmed hadrons ($D0,D^+,D_s,Lambda_C$...), using the displaced vertices of their decay products. The HFT is the first vertex detector to use a new and very promising CMOS Active Pixel Sensor technology. It will allow to build a relatively fast, accurate and radiation tolerant detector, while keeping the material budget low (~ 0.3% $X_0$ per layer). Detector design and physics performance simulations will be presented.