Expected data rates of the CBM-MVD at SIS100 based on realistic beam intensity fluctuations

The Micro-Vertex Detector (MVD) of the CBM experiment will be located close to the collision point and exposed to very high track densities from heavy ion collisions produced at high interaction rates. The design of the MVD requires a detailed knowledge of the detector occupancies and the corresponding data rates, which were simulated in this work. The first step of the study was to determine typical beam intensities for standard systems forseen at SIS-100 i.e. pAu collisions at 30 GeV and Au-Au collisions at 10 A GeV bombarding energy. Two main constrains on the beam intensity were considered: the hit densities and the radiation dose in the 1 MVD station placed 5 cm downstream the target. First, studies demonstrated that a maximal hit density of∼ 17.5 mm−2 can be reached in the MVD per readout cycle [1]. Secondly, simulations of the radiation dose received by the MVD indicated it could endure∼ 5× 10 p-Au and ∼ 5 × 10 Au-Au collisions [2], assuming a non-ionizing radiation hardnesss of 10 neq cm−2. This last value might be in reach for the future sensor at SIS-100, according to measurements performed with MIMOSA-25 featuring a high resistive epitaxial layer [3]. Simulations of the occupancies in the MVD stations located at 5-10-15 cm from the target were peformed using UrQMD + GEANT3.21, as discussed in [4]. These simulations included the production of δ-electrons by the passage of Au ions in the Au target (this is neglected in case of the p-Au collisions). The geometry of the MVD sensors and stations located at 5 and 10 cm from the target were taken according to [6]. The third station was considered by scaling the number of sensors required to satisfy the CBM acceptance. These simulations suggest that in the case of pAu collisions, the beam intensity is limited by the radiation hardness of the MVD to a mean value of ∼ 10 protons/s. As for the Au-Au collisions, the beam intensity is limited by the high hit densities originating from the δ-electrons to a maximal value of ∼ 2 × 10 ions/s. The second step is to estimate the amount of data provided by the MVD sensors in each 30 μs long read-out cycle. To account for the beam fluctuations of SIS-100, we assumed a factor of three for the ratio between the maximum and the average beam intensity. This number was motivated by observations made with the HADES beam diagnostics at SIS-18 [5]. 10 collections of hits created in the sensors in each read-out cycle were simulated assuming a mean fluence of 3 ×104 protons and∼ 200 Au ions pass-