A new tracking system is under development for operation in the CMS experiment at the High Luminosity LHC. It includes an outer tracker which will construct stubs, built by correlating clusters in two closely spaced sensor layers for the rejection of hits from low transverse momentum tracks, and transmit them off-detector at 40 MHz. If tracker data is to contribute to keeping the Level-1 trigger rate at around 750 kHz under increased luminosity, a crucial component of the upgrade will be the ability to identify tracks with transverse momentum above 3 GeV/c by building tracks out of stubs. A concept for an FPGA-based track finder using a fully time-multiplexed architecture is presented, where track candidates are identified using a projective binning algorithm based on the Hough Transform. A hardware system based on the MP7 MicroTCA processing card has been assembled, demonstrating a realistic slice of the track finder in order to help gauge the performance and requirements for a full system. This paper outlines the system architecture and algorithms employed, highlighting some of the first results from the hardware demonstrator and discusses the prospects and performance of the completed track finder.

The Compact Muon Solenoid (CMS) experiment at CERN is scheduled for a major upgrade in the next decade in order to meet the demands of the new High Luminosity Large Hadron Collider. Amongst others, a new tracking system is under development including an outer tracker capable of rejecting low transverse momentum particles by looking at the coincidences of hits (stubs) in two closely spaced sensor layers in the same tracker module. Accepted stubs are transmitted off-detector for further processing at 40 MHz. In order to maintain under the increased luminosity the Level-1 trigger rate at 750 kHz, tracker data need to be included in the decision making process. For this purpose, a system architecture has to be developed that will be able to identify particles with transverse momentum above 3 GeV/c by building tracks out of stubs, while achieving an overall processing latency of maximum 4us. Targeting these requirements the current paper presents an FPGA-based track finding architecture that identifies track candidates in real-time and bases its functionality on a fully time-multiplexed approach. As a proof of concept, a hardware system has been assembled targeting the MP7 MicroTCA processing card that features a Xilinx Virtex-7 FPGA, demonstrating a realistic slice of the track finder. The paper discusses the algorithms' implementation and the efficient utilisation of the available FPGA resources, it outlines the system architecture, and presents some of the hardware demonstrator results.

The CMS collaboration is preparing a major upgrade of its detector, so it can operate during the high luminosity run of the LHC from 2026. The upgraded tracker electronics will reconstruct the trajectories of charged particles within a latency of a few microseconds, so that they can be used by the level-1 trigger. An emulation framework, CIDAF, has been developed to provide a reference for a proposed FPGA-based implementation of this track finder, which employs a Time-Multiplexed (TM) technique for data processing.

A new CMS Tracker is under development for operation at the High Luminosity LHC from 2025. It includes an outer tracker based on PT-modules which will construct tracker stubs, built by correlating clusters in two closely spaced sensor layers for the rejection of low transverse momentum track hits, and transmit them off-detector at 40MHz. If tracker data is to contribute to maintaining the Level1 trigger rate under increased luminosity, a crucial component of the upgrade will be the ability to identify tracks with transverse momentum above 3GeV/c by building tracks out of stubs. A concept for an FPGA-based track finder using a fully time-multiplexed spatially pipelined architecture is presented, where track candidates are identified using a projective binning algorithm. Results from a hardware demonstrator system, where a slice of the track trigger will be constructed to help gauge the performance and requirements for a full system, will be included. Presented at IEEE-RT2016 IEEE-NPSS Real Time Conference (RT) An FPGA-Based Track Finder for the L1 Trigger of the CMS Experiment at the High Luminosity LHC C. Amstutz, F. A. Ball, M. N. Balzer, J. Brooke, L. Calligaris, D. Cieri, E. J. Clement, G. Hall, T. R. Harbaum, K. Harder, P. R. Hobson, G. M. Iles, T. James, K. Manolopoulos, T. Matsushita, A. D. Morton, D. Newbold, S. Paramesvaran, M. Pesaresi, I. D. Reid, A. W. Rose, O. Sander, T. Schuh, C. Shepherd-Themistocleous, A. Shtipliyski, S. P. Summers, A. Tapper, I. Tomalin, K. Uchida, P. Vichoudis, M. Weber for the CMS Collaboration Abstract—A new tracking system is under development for operation in the CMS experiment at the High Luminosity LHC. It includes an outer tracker which will construct stubs, built by correlating clusters in two closely spaced sensor layers for the rejection of hits from low transverse momentum tracks, and transmit them off-detector at 40 MHz. If tracker data is to contribute to keeping the Level-1 trigger rate at around 750 kHz under increased luminosity, a crucial component of the upgrade will be the ability to identify tracks with transverse momentum above 3 GeV/c by building tracks out of stubs. A concept for an FPGA-based track finder using a fully time-multiplexed architecture is presented, where track candidates are identified using a projective binning algorithm based on the Hough Transform. A hardware system based on the MP7 MicroTCA processing card has been assembled, demonstrating a realistic slice of the track finder in order to help gauge the performance and requirements for a full system. This paper outlines the system architecture and algorithms employed, highlighting some of the first results from the hardware demonstrator and discusses the prospects and performance of the completed track finder.A new tracking system is under development for operation in the CMS experiment at the High Luminosity LHC. It includes an outer tracker which will construct stubs, built by correlating clusters in two closely spaced sensor layers for the rejection of hits from low transverse momentum tracks, and transmit them off-detector at 40 MHz. If tracker data is to contribute to keeping the Level-1 trigger rate at around 750 kHz under increased luminosity, a crucial component of the upgrade will be the ability to identify tracks with transverse momentum above 3 GeV/c by building tracks out of stubs. A concept for an FPGA-based track finder using a fully time-multiplexed architecture is presented, where track candidates are identified using a projective binning algorithm based on the Hough Transform. A hardware system based on the MP7 MicroTCA processing card has been assembled, demonstrating a realistic slice of the track finder in order to help gauge the performance and requirements for a full system. This paper outlines the system architecture and algorithms employed, highlighting some of the first results from the hardware demonstrator and discusses the prospects and performance of the completed track finder. I. THE HIGH-LUMINOSITY LARGE HADRON COLLIDER IN order to fully exploit the scientific potential of the Large Hadron Collider (LHC) [1], it is planned to operate the machine at a luminosity up to one order of magnitude above nominal design performance. The High-Luminosity LHC (HLLHC) upgrade [2] is expected to take place during a 30 month shut-down around 2024, facilitating a peak luminosity of 5−7.5×10 cm−2 s−1, corresponding to an average number of proton-proton interactions per 40 MHz bunch crossing, or Manuscript received May 31, 2016. G. Hall, G. M. Iles, T. James, M. Pesaresi, A. W. Rose, A. Shtipliyski, S. P. Summers, A. Tapper, K. Uchida are with Imperial College, London. (GB) L. Calligaris, D. Cieri, K. Harder, K. Manolopoulos, C. ShepherdThemistocleous, I. Tomalin are with STFC Rutherford Appleton Lab. (GB) C. Amstutz, M. N. Balzer, T. R. Harbaum, O. Sander, T. Schuh, M. Weber are with KIT Karlsruhe Institute of Technology (DE) F. A. Ball, J. Brooke, E. J. Clement, D. Newbold, S. Paramesvaran are with the University of Bristol (GB) T. Matsushita is with the Austrian Academy of Science (AT) P. Hobson, A. Morton, I. Reid are with Brunel University London (GB) P. Vichoudis is with CERN European Organization for Nuclear Research This work was supported in part by the the UK Science and Technology Facilities Council. We gratefully acknowledge their support. The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7/2007-2013/ under REA grant agreement nr. 317446 INFIERI ’INtelligent Fast Interconnected and Efficient Devices for Frontier Exploitation in Research and Industry’ Fig. 1. Overview of the CMS detector, as a transverse slice through the barrel [3]. pileup (PU), of 140 to 200. With a targeted total integrated luminosity of 3000 fb−1 the HL-LHC will enable precision Higgs measurements, searches for rare processes that may deviate from the Standard Model and further increase the high mass and low cross-section observation limits into the multiTeV regime. II. THE COMPACT MUON SOLENOID OUTER TRACKER UPGRADE The Compact Muon Solenoid (CMS) is a large, general purpose particle detector at the LHC, designed to investigate a wide range of physics phenomena. It consists of a set of sub-detectors, including the tracking system, surrounding the interaction point, as shown in Fig. 1. A more detailed description of the CMS detector, together with a definition of the coordinate system used and the relevant kinematic variables, can be found in [3]. The complete replacement of the CMS tracker will be necessary during the shut-down preceding the HL-LHC, primarily due to the expected radiation damage of the silicon sensors following ∼ 15 years of operation. The HL-LHC environment will additionally provide a significant challenge for the new tracker [4]. It must maintain a high track reconstruction efficiency and a low misidentification rate under increased pileup conditions. To achieve this the occupancy must be kept at or below the 1% level throughout, requiring an increase in granularity. As a result of increased exposure, the radiation hardness of the tracker must also be improved. 978-1-5090-2014-0/16/$31.00 ©2016 IEEE Fig. 2. Cluster matching in pT-modules. Correlating closely spaced clusters between two sensor layers, separated by a few mm, allows discrimination of transverse momentum based on the particle bend in the CMS magnetic field. Only tracks with pT > 2− 3 GeV/c are transferred to the L1 trigger. The Level-1 (L1) trigger is an event selection system based on custom electronics that uses coarse grained information from the calorimeter and muon sub-detectors to reject events that are not interesting for subsequent physics analysis. Under HL-LHC conditions, increasing the transverse momentum (pT) or transverse energy (ET) thresholds at the L1 trigger would not reduce the rate sufficiently without losses of potentially interesting events, unless some tracking information could be provided to the system. Track-based information would be able to reduce the trigger rate at L1 by validating trigger objects, for example in providing an improved pT assignment to muon triggers which are a major cause of high background rates under increased pileup. However, it is not practical to transfer all tracking data to the L1 trigger. A novel design has therefore been proposed for the outer tracker upgrade, which allows a limited amount of tracking information to be sent to the L1 trigger. The proposed solution [5], [6] utilises two sensors, closely separated (by order millimetres) in the track direction, to discriminate on track pT based on its local bend within the 3.8 T magnetic field, see Fig. 2. Within these pT-modules, charged particles will produce stubs, correlated pairs of clusters, if they are consistent with tracks of transverse momenta greater than a configurable threshold (typically 2-3 GeV/c). In a typical event approximately 98% of charged particles have a pT < 2 GeV/c and these are not considered to be useful for event selection at L1. Therefore by transferring only the stubs to the L1 trigger it is expected that a rate reduction of ∼ 10 is achievable [7], [8] enabling the use of lower bandwidth and lower power optical links for transmission off-detector. Two pT-modules are in development for the tracker upgrade, 2S strip-strip modules, and PS pixel-strip modules, see Fig. 3. The 2S modules are designed to be used at radii r > 60 cm from the beam axis, where the hit occupancies are lower. Both upper and lower sensors consist of ∼ 10 cm×10 cm silicon strip sensors, with a pitch of 90μm in r-φ and 5 cm in z. The PS modules will be used at radii 20 < r < 60 cm where the occupancies are highest. These consist of an upper silicon strip sensor and a lower pixelated sensor, both of dimension Fig. 3. The 2S module (left) and PS module (right), described in the text. z [mm] 0 50