Speaker
Description
The Belle II experiment currently records data at the SuperKEKB $e^+e^-$ collider, which holds the world luminosity record of $5.2\times10^{34}$ $\textrm{cm}^{-2}$ $\textrm{s}^{-1}$ and plans to push up to $6\times10^{35}$ $\textrm{cm}^{-2}$ $\textrm{s}^{-1}$, after an upgrade of its interaction region. To cope with the increased backgrounds, a new fully pixelated vertex detector (VTX) is under design. Spanning from 14 mm to 140 mm from the interaction point, its 5 layers will be instrumented with the same DMAPS, OBELIX, recently submitted for fabrication. The OBELIX sensor is designed in the Tower 180 nm technology, inheriting the pixel matrix from the TJ-Monopix2 sensor, whose characterization has focused on its performance after irradiation with integrated fluences up to the expected $5\times10^{14}$ $1$ $\textrm{MeV}$ $\textrm{n}_\textrm{eq}$ $\textrm{cm}^{-2}$. The new sensor features a 33 µm pitch with a 7-bit Time-Over-Threshold digitization. The new read-out architecture has been designed to support triggered operation and additional features needed for improving time-stamping and contributing to Belle II track triggering. The specifications require the detector to sustain a maximum average hit rate of $120$ $\textrm{MHz}$ $\textrm{cm}^{-2}$, while keeping an overall material budget lower than 3% X0. To meet this target, a light mechanical structure has been pursued, with two different approaches. The ladders of the 2 innermost layers are cut out directly from the processed wafers and connected with a post-process redistributed metal layer. Passive cooling using a thin layer of high-conductance material (TPG) beneath the sensors and connected to actively cooled blocks has been chosen. The post-irradiation performance of TPG was recently validated. The 3 outermost layers, instead, are composed of staggered ladders, realized with a light carbon fibre structure supporting a liquid-cooled plate in contact with the sensors connected to a flex printed cable. This contribution will review the status of the development of the sensor and the detection modules.