Abstract
With the planned addition of the tracking information in the Level-1 trigger in CMS for the High-Luminosity Large Hadron Collider (HL-LHC), the algorithms for the Level-1 trigger can be completely reconceptualized. Following the example for offline reconstruction in CMS to use complementary subsystem information and mitigate pileup, we explore the feasibility of using Particle Flow-like and pileup-per-particle identification techniques at the hardware trigger level. We present the challenges of adapting these algorithm to the timing and resource constraints of the Level-1 trigger, the first prototype implementations, and the expected performance on physics object reconstruction.
Highlights
The Particle Flow (PF) approach aims to reconstruct and identify individually all particles produced in CMS [1] by combining information from all subdetectors [2].Since LHC Run 1, PF has been widely used in the CMS offline and High Level Trigger (HLT) event reconstruction
Benefits have been especially important at low transverse momenta relevant for many physics channels of interest at the High-Luminosity LHC (HL-LHC), e.g. top quark physics, ttH, compressed supersymmetry
Two necessary ingredients for PF are an efficient reconstruction of charged particles in the inner tracker, and a fine granularity calorimetry to resolve the contributions from neighbouring particles
Summary
The Particle Flow (PF) approach aims to reconstruct and identify individually all particles produced in CMS [1] by combining information from all subdetectors [2]. Since LHC Run 1, PF has been widely used in the CMS offline and High Level Trigger (HLT) event reconstruction. Two necessary ingredients for PF are an efficient reconstruction of charged particles in the inner tracker, and a fine granularity calorimetry to resolve the contributions from neighbouring particles. The CMS detector upgrade for HL-LHC [5] will bring key improvements that will make PF possible at the Level-1 Trigger for the first time: A new inner tracker supporting the readout of stubs, pairs of correlated hits in consecutive layers from high pT particles, at the collision rate of 40 MHz, and a backend track finder system to reconstruct all tracks with pT > 2 GeV, |η| < 2.4 within a latency of 4 μs. A new Level-1 trigger system [6] with improved processing power, a global correlator layer allowing complex algorithms using inputs from all trigger subsystems, and deeper buffers in all subsystems to allow a total latency up to 12.5 μs
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