Speaker
Description
The Compact Muon Solenoid (CMS) experiment at the CERN LHC has traditionally relied on a highly selective Level-1 trigger to reduce the 40 MHz LHC collision rate to a rate more manageable for data-reading and recording. This selection inherently limits access to event types with large irreducible backgrounds or with unconventional signatures. During LHC Run 3, CMS deployed a novel 40 MHz data acquisition system that enables the continuous readout and real-time processing of L1 trigger-level detector data at the full bunch-crossing rate, without impacting standard data-taking.
This talk presents the motivation, architecture, and results so far of the CMS L1 scouting system at the LHC Run 3. We describe how modern FPGA-based hardware is leveraged to stream reduced-format calorimeter and muon information into a parallel data path, including the firmware design, online software, and analysis pipelines. Improvements to the system made during 2025 for heavy stable charged particle searches using muon barrel stubs, and work to enable the readout of L1 calorimeter trigger towers will have a particular focus. Recent results of physics studies using the L1 scouting data will be highlighted.
The operational experience during Run 3 will be covered, including the lessons learned from commissioning under real LHC conditions. Finally, we will briefly discuss the physics and detector-performance opportunities unlocked by 40 MHz scouting for future real-time analysis strategies foreseen for the High-Luminosity LHC era.