Open charm measurements at CERN SPS energies in the NA61/SHINE experiment - status and plans

The study of open charm meson production provides an efficient tool for detailed investigations of the properties of hot and dense matter formed in nucleus-nucleus collisions. In particular, charm mesons are of vivid interest in the context of the phase-transition between confined hadronic matter and the quark-gluon plasma. Recently, the experimental setup of NA61/SHINE experiment was supplemented with a small-acceptance version of the Vertex Detector (SAVD) which was motivated by the importance and the possibility of the first direct measurements of open charm mesons in heavy ion collisions at SPS energies. First exploratory data taking of Pb+Pb collisions at 150$A$ GeV/c with SAVD was performed in 2016, and a $D^0$ signal was extracted in it's $D^0 \rightarrow \pi^{+} + K^{-}$ decay channel. This was the first, direct observation of open charm in nucleus-nucleus collisions at the SPS energies. In 2017 and 2018 a large statistic data set has been taken for Xe+La and Pb+Pb with SAVD at 150$A$ GeV/c; these data are currently under intense analysis.Furthermore, the future plans of open charm measurements in the NA61/SHINE experiment related to the upgraded version of the Vertex Detector are discussed.