Construction and test of the demonstrator of the CBM-Micro-Vertex-Detector

The CBM-experiment aims to explore the properties of hadronic matter in the region of highest baryonic densities. One of the major probes of the experiment are open charm particles, which are produced close to the kinematical threshold at CBM beam energies (10-40 AGeV). Reconstructing those rare and short lived (cτ ∼ 100 μm) particles calls for a vacuum compatible vertex detector with an outstandingly high spatial resolution (. 5 μm) and very low material budget (. 0.3 X0). To match those requirements, we aim to build an actively cooled detector based on ultra light and highly granular Monolithic Active Pixel Sensors (MAPS). The MVD-demonstrator project [1] aimed to study the integration of up to four MIMOSA-20 sensors into a detector ladder. MIMOSA-20, which was designed by IPHC Strasbourg, provides a pixel matrix with 640 × 320 pixels with 30× 30 μm pitch. The chip is readout within 2.2 ms via two serial analog outputs submitting each 50 Mpixel/s. Slow control is done via a JTAG interface. Sensors thinned down to 50 μm were successfully operated conjointly with the PLUME-collaboration [2] but not chosen for the MVDdemonstrator for reasons of risk management. Due to a (meanwhile solved) problem in the chip production, the noise of the MIMOSA-20 sensors used was increased to a disappointing value of ∼ 23 e− ENC. The demonstrator was built by wire bonding a three layer flexprint cable top of two sensors. Two of the objects obtained were glued on the opposite faces of a cooling support formed from the highly heat conductive TPG and the ultra light and stiff carbon foam RVC. This support is to transport the heat of the sensors towards a liquid cooled heat sink located outside the acceptance of the future MVD. The sensor control was performed by a dedicated add-on board of the HADES-TRB2, which hosts among others four 12bit ADCs sampling the analogue data stream of the sensors, a VIRTEX4 FPGA and an 1 GB SDRAM module. The demonstrator was intensely tested in laboratory. Vacuum compatibility to fairly below 10−6 mbar was demonstrated with the vacuum vessel of the IKF technology lab. The cooling concept of the ladder was validated