Open charm hadron measurements at STAR

The interaction of the charm quark with the QCD medium created in heavy-ion collisions is sensitive to the medium properties. At the STAR experiment, charm quarks can be studied through open charm hadrons, such as D0 and D*±. We report various measurements of pT spectra of open charm mesons in p+p, Au+Au and U+U collisions and the nuclear modification factors (RAA) extracted from these results. The measured D meson pT spectrum in p+p collisions is consistent with FONLL calculations within uncertainties. In Au+Au and U+U collisions, a significant suppression at high pT and indication of enhancement at intermediate pT are observed for D0 production, which can be described by model calculations with strong charm-medium interaction and coalescence hadronization. In order to improve open heavy flavor measurements, a new Heavy Flavor Tracker (HFT) detector has been built and installed into STAR successfully before the RHIC year 2014 running. The signal significance of reconstructed D0 has been enhanced tremendously with the HFT.