Speakers
Description
The reconstruction of particle decays inside LHCb’s dipole magnet region enables novel measurements of hyperon decays and sensitive searches for long-lived particles with lifetimes above 100 ps, relevant both to the Standard Model and to many of its extensions. Reconstructing such displaced vertices using only track segments in LHCb’s outermost tracker (SciFi) is challenging due to limited momentum resolution, short lever arms, and the need to extrapolate tracks through a strong, inhomogeneous magnetic field around the decay vertex. A new fast-extrapolation strategy has been introduced in the second level of LHCb’s fully software trigger to detect these decays, in which track states are precomputed and cached at multiple positions along the beam line, with trajectories described by cubic-spline interpolation between these anchors. This avoids expensive Runge-Kutta calculations and significantly improves displaced-vertex finding performance, increasing signal yields and purity without impacting throughput. In the first-level trigger, a new high-quality extrapolation is introduced. This approach overcomes GPU memory bottlenecks caused by random access to the magnetic-field map using GPU texture memory. The spatially local caching and hardware-accelerated interpolation substantially reduce extrapolation time, enabling the detection of displaced vertices up to 8 m from the interaction point. Together, these developments enhance the real-time reconstruction and selection of highly displaced vertices within both trigger stages, opening new opportunities for long-lived particle searches at LHCb.