CERN Accelerating science

LHCb Note
Report number	LHCb-PROC-2022-009 ; CERN-LHCb-PROC-2022-009
Title	LHCb’s Forward Tracking algorithm for the Run 3 CPU-based online track reconstruction sequence
Author(s)	Günther, Paul Andre (Heidelberg U.)
Submitted to	Connecting The Dots (CTD 2022), Princeton, United States Of America, 31 May - 2 Jun 2022
Submitted by	[email protected] on 26 Jul 2022
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; LHCb
Free keywords	LHCb ; Flavour Physics
Abstract	In Run 3 of the LHC the LHCb experiment faces very high data rates containing beauty and charm hadron decays. Thus the task of the trigger is not to select any beauty and charm events, but to select those containing decays interesting for the LHCb physics programme. LHCb has therefore implemented a real-time data processing strategy to trigger directly on reconstructed events. The first stage of the purely software-based trigger is implemented on GPUs performing a partial event reconstruction. In the second stage of the software trigger, the full, offline-quality event reconstruction is performed on CPUs, with a crucial part being track reconstruction, balancing track finding efficiency, fake track rate and event throughput. In these proceedings, LHCb's CPU-based track reconstruction sequence for Run 3 is presented, highlighting the "Forward Tracking", which is the algorithm that reconstructs charged particle trajectories traversing all of LHCb's tracking detectors. To meet event throughput requirements, the "Forward Tracking" uses SIMD instructions in several core parts of the algorithm, such as the Hough transform and cluster search. These changes led to an improvement of the algorithm's event throughput by 60%.
Copyright/License	preprint: © 2022 CERN for the benefit of the LHCb collaboration (License: CC-BY-4.0)

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