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Corfu Workshop on Future Accelerators / Selecting long-lived particles in the first trigger level at the LHC

The LHCb is starting to take data in Run 3 with a completely renewed DAQ system. One novel opportunity offered by this system is triggering on long-lived particles at the very first stage of the trigger, running at the full LHC crossing rate of 30 MHz. Moving the selection of V0’s from the second LHCb trigger level (HLT2) to the first (HLT1) is expected to increase trigger efficiency significantly. This is confirmed by a detailed simulation and optimization study, performed on trigger selections based on the presence of either one, or two Ks. Using as benchmarks some specific channels of interest with Ks particles in the final state, like D0-¿KsKs B0-¿KsKs, we obtain large predicted increases in selection efficiency, up to 2.6x for the D0- ¿KsKs channel, at the price of a very modest increase of HLT1 computational load and trigger rate. We therefore proceeded to implement these selections in the GPU-based HLT1 trigger sequence, and acquired data during the physics data-taking LHCb run in year 2022. In this talk, we present the results obtained from the first data collected with this unique trigger, yielding good quality Ks and Ks-pair samples even from a very limited integrated luminosity. We conclude with a discussion of the physics prospects opened by this new trigger, and its planned extension to tracks decaying outside the volume of the VELO subdector (”downstream tracks”), that will further increase its acceptance for LLP

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