Open charm measurements at CERN SPS energies with the new Vertex Detector of the NA61/SHINE experiment
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. The interpretation of the existing data from the CERN SPS suffers from a lack of knowledge on the total charm production rate. To overcome this limitation the heavy-ion programme of the NA61/SHINE experiment at CERN SPS has been expanded to allow for precise measurements of particles with a short lifetime. A new Small Acceptance Vertex Detector (SAVD) was designed and constructed to meet the challenges of open charm measurements in nucleus-nucleus collisions. SAVD was installed in December 2016 for data taking with Pb+Pb collisions at 150$A$ GeV/c. An exploratory set of collected data allowed to validate the general concept of the $D^0$ mesons detection via its $D^0 \rightarrow \pi^+ + K^-$ decay channel and delivered the first direct observation of open charm at SPS energies. In October and November of 2017 a large statistic data set has been taken for Xe+La at 150$A$, 75$A$, and 40$A$ GeV/c, these data are currently under intense analysis. The physics motivation behind the open charm measurements at the SPS energies will be discussed. Moreover, the concept of the SAVD hardware and status of the analysis will be shown. Also, the future plans of open charm measurements in the NA61/SHINE experiment related to the upgraded Vertex Detector will be presented.