Abstract

The Pixel Detector is the innermost detector of the tracking system of the Compact Muon Solenoid (CMS) experiment at CERN Large Hadron Collider (LHC) . It precisely determines the interaction point (primary vertex) of the events and the possible secondary vertexes due to heavy flavours (b and c quarks); it is part of the overall tracking system that allows reconstructing the tracks of the charged particles in the events and combined with the magnetic field to measure their momentum. The pixel detector allows measuring the tracks in the region closest to the interaction point. The Level-1 (real-time) pixel based tracking trigger is a novel trigger system that is currently being studied for the LHC upgrade. An important goal is developing real-time track reconstruction algorithms able to cope with very high rates and high flux of data in a very harsh environment. The pixel detector has an especially crucial role in precisely identifying the primary vertex of the rare physics events from the large pile-up (PU) of events. The goal of adding the pixel information already at the real-time level of the selection is to help reducing the total level-1 trigger rate while keeping an high selection capability. This is quite an innovative and challenging objective for the experiments upgrade for the High Luminosity LHC (HL-LHC) . The special case here addressed is the CMS experiment. This document describes exercises focusing on the development of a fast pixel track reconstruction where the pixel track matches with a Level-1 electron object using a ROOT-based simulation framework.

Highlights

  • A new Front End and readout system is currently developed within the R&D (RD53) Collaboration [6] for the HL-Large Hadron Collider (LHC) era (2023-2025)

  • The PiXTRK algorithm we are using here and that has been developed for ongoing feasibility studies in Compact Muon Solenoid (CMS) for High Luminosity LHC (HL-LHC), performs the pattern recognition

  • PiXTRK transfers to Level-1 what is achieved in the first stage of the current CMS High Level Trigger (HLT), namely the matching of pixel hits with the EM cluster [3]

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Summary

The upgrade of the Pixel detector from Phase 1 to Phase 2

The present CMS pixel detector consists of three barrel layers with two endcap disks that covers a pseudorapidity range |η| < 2.5, matching the acceptance of the central tracker [1]. A first upgrade for Phase 1 (around 2018) of the current pixel detector will add a fourth barrel layer, a third disk on each endcap sides, as well as a new Front End ASIC including signal digitization, and a new readout chain with higher performance in speed and bandwidth. In the Phase 2 upgrade for HL-LHC, the CMS pixel detector will have an extended pseudorapidity coverage up to |η| < 4 as shown in figure 1 [5]. It will be made of new pixel sensors (the sensor technology is being selected) and of smaller size pixels (higher granularity). A new Front End and readout system is currently developed within the R&D (RD53) Collaboration [6] for the HL-LHC era (2023-2025)

The L1 pixel based Electron trigger algorithm
Pattern recognition seeded by the L1 EM cluster It follows two steps
Refined Pattern recognition seeded by the EM cluster
The standalone pattern recognition
EXERCISES
Findings
Conclusion
Full Text
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