Speaker
Description
The present contribution focuses on the last two years of test beam campaign performed in the context of the CMS Phase 2 luminosity, at the CERN-PS T9 beamline. The systems under test were both the new luminometer Fast Beam Condition Monitor (FBCM), and the new Inner Tracker pixel detectors based on the RD53B ASIC.
The FBCM detector is based on arrays of 6 square silicon pads of the size of about 1.9 mm. A dedicated ASIC was developed in order to read and control the sensor, providing as output a fast asynchronous comparator signal which is then processed by the lpGBT ASIC to compute precise Time of Arrival (ToA) and Time over Threshold (ToT) digital output. This is then sent via optical fiber after VTRx+ electrical to optical conversion to the back-end FPGA boards. The used Inner Tracker pixel sensors had a cell size of either 100×25 μm$^2$ and 50×50 μm$^2$, for a total 145152 pixels and a detector size of roughly 2×2 cm$^2$. The sensor was read out by the RD53B ASIC, counting 432 × 336 channels and performing signal digitization directly on chip: the digital output was both directly processed electrically or converted optically using the lpGBT ASIC and VTRx+.
Other than testing the performance of the FBCM detector, a conspicuous part of the campaign was dedicated to the development and optimization of the back-end firmware and readout. The focus for FBCM has been to correctly readout and histogram in firmware both ToT and ToA data, producing lightweight online histogram output: this will be the final design for CMS Phase 2. The possibility of accessing FBCM raw data was also added in firmware, pairing the FBCM Silicon pads both to a MIMOSA 6-planes telescope and a Inner Tracker pixel detector using an AIDA Trigger Logic Unit (TLU).
This setup was critical to estimate the detector performance of fresh and irradiated FBCM sensors. Concerning the Inner Tracker, other than using it to create a precise trigger mask for the FBCM detector, dedicated firmware algorithms for online clustering of the pixel data have been tested successfully.
Back-end architecture and online software control saw important advancements during the whole campaign: starting from back-end electronics based on the μTCA standard, for which the first prototypes of firmware and software DAQ have been developed and tested successfully, we moved to the final ATCA standard. ATCA required the use of a more sophisticated architecture, in which a Data and Timing Hub (DTH) board was used for timing, and the Apollo ATCA board was used for both Inner Tracker and FBCM front-end readout and control.
Dedicated firmware and software were developed to process data, calibrate and control the detectors with the new back-end architecture, and dedicated PCBs were also developed in order to enable triggering using the Apollo board and Inner Tracker front-end. This was the first beam physics data acquired with ATCA back-end for both FBCM and Inner Tracker.
The DAQ was based on dedicated IPBus firmware and software: detector performance was extracted, allowing to probe expected out-of-time events for the future Inner Tracker, and charge collection efficiency loss for FBCM. Overall, the system looks promising and with broad applications in test beam environments; further improvements will be tested in a final 2026 campaign.