Speaker
Description
The CMS experiment 40MHz Scouting project is aimed at intercepting the data produced at the level of the detectors' front-end without the filters induced by hardware-based Triggers. A first 40MHz Scouting implementation is realized by reading a slice of the Drift Tube (DT) muon detector, equipped with so-called Phase-2 Upgrade front-end boards. The data are transferred via high-speed optical links to back-end boards independently from the central DAQ, permitting to monitor in real-time the detectors' status spying all the signals produced at the front-end level, and providing an unbiased estimate of the CMS DT hit-rate under various data-taking conditions.
Summary (500 words)
The 40 MHz Level-1 Scouting System of CMS is conceived to spy intermediate stages of the trigger processing system, aiming to perform data analysis at the bunch-crossing rate. The Scouting project aims at providing a parallel readout chain, processing copies of the output streams feeding the components of the Level-1 trigger at 40 MHz. The trigger data are extracted through high-bandwidth optical links towards input electronics that store the data on host memory. Once left the trigger generation path, the processing can be carried out in an asynchronous way by means of dedicated computing resources.
The Level-1 Scouting can be complemented by extracting the raw stream of data from the detectors' front-end electronics, provided that the expected data throughput is manageable for the links' bandwidth. The trigger-less readout of the raw data provides real-time diagnostics of the detector status and invaluable monitoring of the quality of the collected data, based on the completely unfiltered online data stream. The analysis of raw data will further open the stage for the reconstruction of physics processes without the rate limitations and the bias induced by the Level-1 trigger filtering stages, leveraging on distributed computing frameworks.
The Drift Tube (DT) muon spectrometer is an excellent candidate for the first implementation of a trigger-less readout system in CMS due to its low detector occupancy. A 40 MHz scouting for a Phase-2 Upgrade CMS detector demonstrator has been implemented on the so-called DT Phase-2 Slice Test. The scouting of the DTs raw data has been made possible by the added functionalities of the new Phase-2 front-end board, the OBDT (On detector Board for the Drift Tube chambers), which transfers the digitized signals on high-speed optical links using the GBTx protocol. The links received at the back-end by commercial off-the-shelf boards are transferred using Direct Memory Access over the PCI-express bus of dedicated servers, where the data stream is processed in software for the monitoring of the detectors, both offline and in real-time. The 40 MHz scouting of the CMS DT Phase-2 Slice Test is fully decoupled from other components of the CMS DT readout chain, as it collects data parasitically and independently from the central CMS DAQ or trigger systems. The data collected are used for a first estimation of the unbiased CMS DT hit rate under different data-taking conditions.
