Giuliana Rizzo, INFN and University, Pisa ; Belle II VTX Upgrade Group

28 May 2024
16th Pisa Meeting on Advanced Detectors

Abstract: Abstract: The SuperKEKB collider will undergo a major upgrade at the end of the decade to reach the target luminosity of 6 10^35 cm-2 s-1, offering the opportunity to install a new pixelated vertex detector (VTX) for the Belle II experiment. The VTX will be more robust against the expected higher level of machine background and more performant in terms of standalone track finding efficiency. The VTX design matches the modified interaction region and includes five layers, spanning radii from 14 mm to 135 mm. All layers are equipped with the same depleted-MAPS, OBELIX, designed in the Tower 180 nm technology, which pixel matrix is derived from the TJ-Monopix2 sensor originally developed for the ATLAS experiment. Featuring a 33 µm pitch, OBELIX integrates hits over 100 ns while dissipating less than 200 mW/cm2 at an average hit rate of 60 MHz/cm2. The digital trigger logic matches the 30 kHz average Belle II trigger rate with 10 µs trigger delay and a maximum hit rate of 120 MHz/cm2. The two innermost layers (iVTX) have a sensitive length of about 12 cm and aim for a material budget below 0.2 % X0/layer, benefitting from air cooling. One ladder is made of a 4-sensor wide module cut out from processed wafers and submitted to post-processing operations in order to connect them at one end. The three outer layers (oVTX) target material budget ranging from 0.3 % X0 for the shortest length up to 0.8 % X0 for the 70 cm-long and outermost layer. The ladder concept uses a light mechanical structure supporting a liquid-cooled plate in contact with the sensors connected to a flex printed cable. We will review all project aspects: tests of the TJ-Monopix2 sensor, OBELIX-1 design status, prototype fabrication and tests for the iVTX and oVTX concepts, including their cooling.

Keyword(s): upgrade ; VXD ; VTX ; CMOS ; MAPS ; DMAPS ; vertex ; vertex detector
Note: 17+3