Upgraded CMS Fast Beam Condition Monitor for LHC Run 3 Online Luminosity and Beam Induced Background Measurements

The fast Beam Condition Monitor (BCM1F) for the CMS experiment at the LHC was upgraded for precision luminosity measurement in the demanding conditions foreseen for LHC Run 3. BCM1F has been rebuilt with new silicon diodes, produced on the CMS Phase 2 Outer Tracker PS silicon wafers. The mechanical structure was adapted to include a 3D printed titanium circuit for active cooling of BCM1F sensors. The assembly and qualification of the detector quadrants were followed by the integration with Pixel Luminosity Telescope and Beam Conditions Monitor for Losses on a common carbon fibre carriage. This carriage was installed inside the CMS behind the Pixel detector, 1.9 m from the Interaction Point. BCM1F will provide a real-time luminosity measurement as well as a measurement of the beam-induced background, by exploiting the arrival time information of the hits with a sub-bunch crossing precision. Moreover, regular beam overlap scans at CMS were introduced during Run 2, enabling an independent and non-destructive transverse profile measurement for LHC Operators. The paper describes the improved BCM1F detector design, its commissioning and performance during the beginning of Run 3 operation.