An efficient and precise reconstruction of charged-particle tracks is crucial for the overall performance of the CMS experiment. During Run 2 of LHC, significant upgrades were made to the track reconstruction algorithms in order to accommodate for the high pileup environment and the installation of an upgraded pixel detector in 2017. This paper provides an overview of the iterative track reconstruction algorithm used in CMS during Run 2 and of the performance measured both with simulated and collision data. Developments are ongoing to further improve track reconstruction in Run 3, especially for what concerns the CMS high-level trigger, and the status of these improvements will be discussed.
The expected performance of track reconstruction with LHC events using the CMS silicon tracker is presented. Track finding and fitting is accomplished with Kalman Filter techniques that achieve efficiencies above 99% on single muons with pT>1 GeV/c. Difficulties arise in the context of standard LHC events with a high density of charged particles, where the rate of fake combinatorial tracks is very large for low pT tracks, and nuclear interactions in the tracker material reduce the tracking efficiency for charged hadrons. Recent improvements with the CMS track reconstruction now allow to effici…
The 2009 run provided the first proton-proton collisions from the Large Hadron Collider (LHC) at center of mass energies of 900 GeV and 2.36 TeV. The Compact Muon Solenoid (CMS) experiment has recorded a large sample of minimum bias events from these collisions. We present results from the all silicon tracking detectors from this run. The performance of the tracker and track reconstruction algorithms are considered including signal-to-noise, efficiencies and comparisons to simulation for track parameter and resonance reconstruction performance.
The High-Luminosity LHC is expected to deliver proton-proton collisions every 25 ns with an estimated 140-200 pileup interactions per bunch crossing. Ultrafast track finding is vital for handling Level 1 trigger rates in such conditions. An FPGA-based track trigger system, capable of finding tracks with momenta above 2 GeV, is presented.
The LHC machine is planning an upgrade program, which will smoothly bring the instantaneous luminosity to about $5-7.5\times10^{34}~\mathrm{cm}^{-2}\mathrm{s}^{-1}$ in 2028, to possibly reach an integrated luminosity of 3000-4500 fb$^{-1}$ by the end of 2039. This High-Luminosity LHC scenario, HL-LHC, will require a preparation program of the LHC detectors known as Phase-2 upgrade. The current CMS Outer Tracker, already running beyond design specifications, and the recently installed CMS Phase-1 Pixel Detector will not be able to survive the HL-LHC radiation conditions. Thus, CMS will need com…
The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ioniz…
During the High Luminosity LHC, the CMS detector will need charged particle tracking at the hardware trigger level to maintain a manageable trigger rate and achieve its physics goals. The tracklet approach is a track-finding algorithm based on a road-search algorithm that has been implemented on commercially available FPGA technology. The tracklet algorithm has achieved high performance in track-finding and completes tracking within 3.4 $μ$s on a Xilinx Virtex-7 FPGA. An overview of the algorithm and its implementation on an FPGA is given, results are shown from a demonstrator test stand and s…
In the upcoming years, with the upgrade of the LHC to higher luminosities, CMS will be subject to an increasing flux of particles, especially in its most forward region, at | η| > 1.6. To consolidate the muon spectrometer of CMS and increase redundancy, the CMS GEM collaboration proposes to instrument the 1.6 < | η| < 2.1 region, originally foreseen to be equipped with RPC, with Triple-GEM detectors. This technology has proven to remain efficient under high fluxes and meets the requirements of CMS. This work, using simulations, studies three track reconstruction algorithms intended to be insta…
The strategies for and the performance of the CMS tracker alignment during the 2021-2022 LHC commissioning preceding the Run 3 data-taking period are described. The results of the very first tracker alignment after the pixel reinstallation, performed with cosmic ray muons recorded with the solenoid magnet off are presented. Also, the performance of the first alignment of the commissioning period with collision data events, collected at center-of-mass energy of 900 GeV, is presented. Finally, the tracker alignment effort during the final countdown to LHC Run 3 is discussed.
This conference proceeding presents the first results of the full CMS Tracker alignment based on several million reconstructed tracks from the cosmic data taken during the commissioning runs with the detector in its final position and magnetic field present. The all-silicon design of the CMS Tracker poses new challenges in aligning a complex system with 15\,148 silicon strip and 1440 silicon pixel modules. For optimal track-parameter resolution, the position and orientation of its modules need to be determined with a precision of about one micrometer. The modules, well illuminated by cosmic ra…
A Kalman Filter alignment algorithm has been applied to cosmic-ray data. We discuss the alignment algorithm and an experiment-independent implementation including outlier rejection and treatment of weakly determined parameters. Using this implementation, the algorithm has been applied to data recorded with one CMS silicon tracker endcap. Results are compared to both photogrammetry measurements and data obtained from a dedicated hardware alignment system, and good agreement is observed.
With the High Luminosity LHC upgrades, incorporating tracking information into the CMS Level-1 trigger becomes necessary in order to maintain a manageable trigger rate and good trigger performance e.g. to retain thresholds for electroweak physics. The main challenges Level-1 track finding faces are the large data throughput from the detector at a collision rate of 40 MHz and a 4 microsecond latency budget to reconstruct charged particle tracks with sufficiently low transverse momentum to be used in the Level-1 trigger decision. Dedicated all-FPGA hardware systems with time-multiplexed architec…
The CMS silicon tracker consists of two tracking devices utilizing semiconductor technology: the inner pixel and the outer strip detectors. They operate in a high-occupancy and high-radiation environment presented by particle collisions in the LHC. The tracker detectors occupy the region around the center of CMS, where the LHC beams collide, between 4 cm and 110 cm in radius and up to 280 cm along the beam axis. The pixel detector consists of 66 million pixels, covering about 1 m2 total area. It is surrounded by the strip tracker with 10 million read-out channels covering about 200 m2 total ar…
The strategies for and the performance of the CMS silicon tracking system alignment during the 2015-2018 data-taking period of the LHC are described. The alignment procedures during and after data taking are explained. Alignment scenarios are also derived for use in the simulation of the detector response. Systematic effects, related to intrinsic symmetries of the alignment task or to external constraints, are discussed and illustrated for different scenarios.
The CMS tracker consists of 206 square meters of silicon strip sensors assembled on carbon fibre composite structures and is designed for operation in the temperature range from -25 to +25 degrees C. The mechanical stability of tracker components during physics operation was monitored with a few micron resolution using a dedicated laser alignment system as well as particle tracks from cosmic rays and hadron-hadron collisions. During the LHC operational period of 2011-2013 at stable temperatures, the components of the tracker were observed to experience relative movements of less than 30 micron…
The Resistive Plate Chambers detector system at the CMS experiment at the LHC provides robustness and redundancy to the muon trigger. A total of 1056 double-gap chambers cover the pseudo-rapidity region < 1.6. The main detector parameters and environmental conditions are constantly and closely monitored to achieve operational stability and high quality data in the harsh conditions of the second run period of the LHC with center-of-mass energy of 13 TeV. First results of overall detector stability with 2015 data and comparisons with data from the LHC RUN-1 period at 8 TeV are presented.
At the High Luminosity LHC (HL-LHC), the CMS experiment will face a harsh environment with a high instantaneous luminosity up to 7x10$^{34}$/cm$^2$/s corresponding to an average of 140-200 multiple proton-proton collisions per bunch crossing. The main goal of the CMS Level 1 (L1) trigger upgrade for the HL-LHC is to maintain trigger thresholds that are as low as possible and comparable to those currently in use at the LHC, and to possibly include new triggers that were not feasible at the LHC. This will be achieved by upgrading the detector readout electronics, to allow a much larger L1 trigge…
The inner tracking system of the CMS experiment, which comprises Silicon Pixel and Silicon Strip detectors, is designed to provide a precise measurement of the momentum of charged particles and to reconstruct the primary and secondary vertices. The movements of the different substructures of the tracker detectors driven by the operating conditions during data taking, require to regularly update the detector geometry in order to accurately describe the position, orientation, and curvature of the tracker modules. The procedure in which new parameters of the tracker geometry are determined is kno…
The CMS experiment collected around 150 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}$ = 13 TeV during the Run-2 data taking period of LHC. The CMS RPC system provided redundant information for robust muon triggering, reconstruction and identification. To ensure stable data taking, the CMS RPC collaboration has performed detector operation, calibration and performance studies. After the end of Run-2, it was started the second LHC long shutdown period (LS2), an important opportunity for maintenance and preparation for the next data taking period (Run-3) and the installation of services…
The strategy for track based alignment of the CMS tracking and muon detectors is presented. After an overview over the used data samples, the general alignment strategy is presented, with a focus of the procedures envisaged at the start of data taking in 2008. The three currently used alignment algorithms are discussed and first results on their application to the CMS tracker are presented, as well as studies on the alignment of the Muon detector with tracks.
A description is provided of the software algorithms developed for the CMS tracker both for reconstructing charged-particle trajectories in proton-proton interactions and for using the resulting tracks to estimate the positions of the LHC luminous region and individual primary-interaction vertices. Despite the very hostile environment at the LHC, the performance obtained with these algorithms is found to be excellent. For ttbar events under typical 2011 pileup conditions, the average track-reconstruction efficiency for promptly-produced charged particles with transverse momenta of pt > 0.9 GeV…
The Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) is designed to study a wide range of high energy physics phenomena. It employs a large all-silicon tracker within a 3.8 T magnetic solenoid, which allows precise measurements of transverse momentum ($p_\mathrm{T}$) and vertex position. This tracking detector will be upgraded to coincide with the operation of the High-Luminosity LHC, which will provide luminosities of up to $7.5\,\times\,10^{35}\,\mathrm{cm^{-2}s^{-1}}$ to CMS, or 200 collisions per 25 ns bunch crossing. This new tracker must maintain the nominal phys…
During autumn 2008, the Silicon Strip Tracker was operated with the full CMS experiment in a comprehensive test, in the presence of the 3.8 T magnetic field produced by the CMS superconducting solenoid. Cosmic ray muons were detected in the muon chambers and used to trigger the readout of all CMS sub-detectors. About 15 million events with a muon in the tracker were collected. The efficiency of hit and track reconstruction were measured to be higher than 99% and consistent with expectations from Monte Carlo simulation. This article details the commissioning and performance of the Silicon Strip…
Between 2025 and 2027, some essential components of the CMS (Compact Muon Solenoid) detector - most notably the tracker and the calorimeter endcap - will be upgraded to prepare for HL-LHC (High Luminosity Large Hadron Collider) conditions. The upgraded CMS Outer Tracker and parts of the new CMS High Granularity Calorimeter (HGCAL) will encompass over $50{,}000$ new silicon sensors covering a total area of about $800\,\text{m}^{2}$. The sensor series production requires a dedicated strategy to monitor the quality and stability of the production process. The strategy is based on a test structure…
The High-Luminosity LHC will put significant demands on trigger systems. To control trigger thresholds, the CMS Collaboration is designing a novel Level-1 track trigger. The Outer Tracker will use modules with pairs of sensor layers to read out hits compatible with charged particles above 2-3 GeV. The system will combine these front-end trigger primitives to reconstruct tracks, providing a measurement of $p_{\mathrm{T}}$, $η$ , $ϕ$, and $z_{0}$. This presentation will introduce the CMS L1 track finding system: the algorithm and its estimated performance, hardware prototypes, and the unique cha…
One of the most computationally challenging problems expected for the High-Luminosity Large Hadron Collider (HL-LHC) is finding and fitting particle tracks during event reconstruction. Algorithms used at the LHC today rely on Kalman filtering, which builds physical trajectories incrementally while incorporating material effects and error estimation. Recognizing the need for faster computational throughput, we have adapted Kalman-filter-based methods for highly parallel, many-core SIMD and SIMT architectures that are now prevalent in high-performance hardware. Previously we observed significant…
Hardware-based track reconstruction in the CMS and ATLAS trigger systems for the High-Luminosity LHC upgrade will provide unique capabilities. An overview is presented of earlier track trigger systems at hadron colliders, in particular for the Tevatron CDF and D0 experiments. We discuss the plans of the CMS and ATLAS experiments to implement hardware-based track reconstruction for the High-Luminosity LHC. Particular focus is placed on the track trigger capability of the upgraded CMS experiment. We discuss the challenges and opportunities of this novel handle, and review the alternatives that w…
The challenging conditions of the High-Luminosity LHC require tailored hardware designs for the trigger and data acquisition systems. The Apollo platform features a "Service Module" with a powerful system-on-module computer that provides standard ATCA communications and application-specific "Command Module"s with large FPGAs and high-speed optical fiber links. The CMS version of Apollo will be used for the track finder and the pixel readout. It features up to two large FPGAs and more than 100 optical links with speeds up to 25\,Gb/s. We study carefully the design and performance of the board b…
This report presents recent results on track reconstruction and alignment with the silicon tracker of the CMS experiment at the LHC, obtained with a full detector simulation. After an overview of the layout of the tracker and its material budget, the baseline algorithm for track reconstruction is discussed. The performance of the track reconstruction and its dependence on misalignment is shown. The concept for alignment of the CMS tracker, using a laser alignment system as well as three different track-based alignment algorithms, is presented.
The CMS muon system has played a key role for many physics results obtained from the LHC Run-1 data. During the Long Shutdown (2013-2014) significant upgrades have been carried out on the muon detectors and on the L1 muon trigger. In parallel the algorithms for muon reconstruction and identification have been improved for both the High-Level Trigger and the offline reconstruction. Results of studies performed on data and Monte Carlo simulations will be presented, with focus on the improvements aiming to ensure an excellent performance in conditions of multiplicity of pileup events and bunch sp…
The CMS Inner Tracker, made of silicon pixel modules, will be entirely replaced prior to the start of the High Luminosity LHC period. One of the crucial components of the new Inner Tracker system is the readout chip, being developed by the RD53 Collaboration, and in particular its analogue front-end, which receives the signal from the sensor and digitizes it. Three different analogue front-ends (Synchronous, Linear, and Differential) were designed and implemented in the RD53A demonstrator chip. A dedicated evaluation program was carried out to select the most suitable design to build a radiati…
The inner silicon detector of the Compact Muon Solenoid experiment (CMS) at CERN's LHC consists of 16588 modules. Charged-particle tracks in the detector are used to improve the accuracy to which the position and orientation of the modules is known. This contribution focuses on the Millepede-II algorithm, one of the two alignment algorithms used by CMS. Recently an advanced track model has been introduced into the CMS alignment procedure, which is based on the "Broken Lines" model and is able to take multiple Coulomb scattering in the detector material properly into account. We show the unique…
The CMS electromagnetic calorimeter (ECAL) is a high-resolution, hermetic, and homogeneous calorimeter made of 75,848 scintillating lead tungstate crystals. Following the discovery of the Higgs boson, the CMS ECAL is at the forefront of precision measurements and the search for new physics in data from the LHC, which recently began producing collisions at the unprecedented energy of 13 TeV. The exceptional precision of the CMS ECAL, as well as its timing performance, are invaluable tools for the discovery of new physics at the LHC Run 2. The excellent performance of the ECAL relies on precise …
The contribution of Resistive Plate Chamber (RPC) to muon reconstruction in CMS has been studied on a sample of muons collected in proton-proton collisions at sqrt(s) = 7 TeV at the LHC in 2011. Muon reconstruction is performed using the all-silicon inner tracker and with up to four stations of gas-ionization muon detectors. Drift Tubes and Cathode Strip Chambers detect muons in the barrel and endcap regions, respectively, and are complemented by the RPC system. Measured distributions of reconstructed hits in the RPCs crossed by muons from Z decays with a transverse momentum pT above 20 GeV/c …
The era of High-Luminosity Large Hadron Collider will pose unprecedented challenges for detector design and operation. The planned luminosity of the upgraded machine is 5-7.5 x 10$^{34}$ cm$^{-2}$ s$^{-1}$, reaching an integrated luminosity of 3000-4000 fb$^{-1}$ by the end of 2039. The CMS Tracker detector will have to be replaced in order to fully exploit the delivered luminosity and cope with the demanding operating conditions. The new detector will provide robust tracking as well as input for the first level trigger. This report is focusing on the replacement of the CMS Outer Tracker syste…
The results of the CMS tracker alignment analysis are presented using the data from cosmic tracks, optical survey information, and the laser alignment system at the Tracker Integration Facility at CERN. During several months of operation in the spring and summer of 2007, about five million cosmic track events were collected with a partially active CMS Tracker. This allowed us to perform first alignment of the active silicon modules with the cosmic tracks using three different statistical approaches; validate the survey and laser alignment system performance; and test the stability of Tracker s…
The Compact Muon Solenoid (CMS) is one of two general-purpose detectors that reconstruct the products of high energy particle interactions at the Large Hadron Collider at CERN. The silicon pixel detector is the innermost component of the CMS tracking system. It determines the trajectories of charged particles originating from the interaction region with high resolution enabling precise momentum and impact parameter measurements in the tracker. It is designed to operate in the high particle density environment of the LHC. The calibration of the pixel detector plays an important role in its perf…
The subsystems of the CMS silicon strip tracker were integrated and commissioned at the Tracker Integration Facility (TIF) in the period from November 2006 to July 2007. As part of the commissioning, large samples of cosmic ray data were recorded under various running conditions in the absence of a magnetic field. Cosmic rays detected by scintillation counters were used to trigger the readout of up to 15% of the final silicon strip detector, and over 4.7 million events were recorded. This document describes the cosmic track reconstruction and presents results on the performance of track and hi…
The High Luminosity Large Hadron Collider (HL-LHC) at CERN is expected to collide protons at a centre-of-mass energy of 14\,TeV and to reach the unprecedented peak instantaneous luminosity of 5\,$-$\,7.5\,x\,$10^{34}$\,cm$^{-2}$s$^{-1}$ with an average number of pileup events of 140\,$-$\,200. This will allow the ATLAS and CMS experiments to collect integrated luminosities up to 3000\,$-$\,4000\,fb$^{-1}$ during the project lifetime. To cope with this extreme scenario the CMS detector will be substantially upgraded before starting the HL-LHC, with a plan known as CMS Phase-2 upgrade. The CMS T…
High-Luminosity running at the LHC, which is planned for 2022 and beyond, will imply an order of magnitude increase in radiation levels and particle fluences with respect to the present LHC running conditions. The performance evolution of the CMS electromagnetic calorimeter (ECAL), comprising 75,848 scintillating lead tungstate crystals, indicates that an upgrade of its endcaps will be needed for HL-LHC running, to ensure an adequate performance. Results from LHC collision periods, beam tests and laboratory measurements of proton-irradiated crystals are combined to predict the performance of t…
The CMS collaboration aims at improving the muon trigger and tracking performance at the HL-LHC by installing new Gas Electron Multiplier (GEM) chambers in the endcaps of the CMS experiment. Construction and commissioning of GEM chambers for the first muon endcap stations is ramping up in several laboratories using common quality control protocols. The SCRIBE framework is a scalable and cross-platform webbased application for the RD51 Scalable Readout System (SRS) that controls data acquisition and analyzes data in near real time. It has been developed mainly to simplify and standardize measur…
The High-Luminosity upgrade of the LHC will see the accelerator reach an instantaneous luminosity of $7\times 10^{34} cm^{-2}s^{-1}$ with an average pileup of $200$ proton-proton collisions. These conditions will pose an unprecedented challenge to the online and offline reconstruction software developed by the experiments. The computational complexity will exceed by far the expected increase in processing power for conventional CPUs, demanding an alternative approach. Industry and High-Performance Computing (HPC) centres are successfully using heterogeneous computing platforms to achieve highe…
In Run 1 of the Large Hadron Collider, software and computing was a strategic strength of the Compact Muon Solenoid experiment. The timely processing of data and simulation samples and the excellent performance of the reconstruction algorithms played an important role in the preparation of the full suite of searches used for the observation of the Higgs boson in 2012. In Run 2, the LHC will run at higher intensities and CMS will record data at a higher trigger rate. These new running conditions will provide new challenges for the software and computing systems. Over the two years of Long Shutd…
The complex system of the CMS all-silicon Tracker, with 15\,148 silicon strip and 1440 silicon pixel modules, requires sophisticated alignment procedures. In order to achieve an optimal track-parameter resolution, the position and orientation of its modules need to be determined with a precision of few micrometers. The alignment of pixels modules is crucial for the analyses requiring a precise vertex reconstruction. The aligned geometry is based on the analysis of several million reconstructed tracks recorded during the commissioning of the CMS experiment, both with cosmic rays and with the fi…
The high instantaneous luminosities expected following the upgrade of the Large Hadron Collider (LHC) to the High Luminosity LHC (HL-LHC) pose major experimental challenges for the CMS experiment. A central component to allow efficient operation under these conditions is the reconstruction of charged particle trajectories and their inclusion in the hardware-based trigger system. There are many challenges involved in achieving this: a large input data rate of about 20--40 Tb/s; processing a new batch of input data every 25 ns, each consisting of about 15,000 precise position measurements and ro…
In the high luminosity scenario of the LHC (HL-LHC), which will bring the instantaneous luminosity up to 7.5\,$\times$\,$10^{34}$\,cm$^{-2}$s$^{-1}$, ATLAS and CMS will need to operate at up to 200 interactions per 25\,ns beam crossing and reaching up to 4000\,fb$^{-1}$ of integrated luminosity. To achieve their physics goals the experiments will need to improve the tracking and vertexing capability and the ability to selectively trigger on specific physics events at reasonable thresholds. The upgrade of the CMS Tracker requires designing new inner and outer tracking detectors to cope with the…
The powerful muon and tracker systems of the CMS detector together with dedicated reconstruction software allow precise and efficient measurement of muon tracks originating from proton-proton collisions. The standard muon reconstruction algorithms, however, are inadequate to deal with muons that do not originate from collisions. We present the design, implementation, and performance of a dedicated cosmic muon track reconstruction algorithm, which features pattern recognition optimized for muons that are not coming from the interaction point, i.e. cosmic muons and beam-halo muons. To evaluate t…
The CMS experiment recorded 177.75 /fb of proton-proton collision data during the RUN-1 and RUN-2 data taking period. Successful data taking at increasing instantaneous luminosities with the evolving detector configuration was a big achievement of the collaboration. The CMS RPC system provided redundant information for the robust muon triggering, reconstruction, and identification. To ensure stable data taking, the CMS RPC collaboration has performed detector operation, calibration, and performance studies. Various software and related tools are developed and maintained accordingly. In this pa…
The trigger systems of the LHC detectors play a crucial role in determining the physics capabilities of the experiments. A reduction of several orders of magnitude of the event rate is needed to reach values compatible with the detector readout, offline storage and analysis capabilities. The CMS experiment has been designed with a two-level trigger system: the Level 1 (L1) Trigger, implemented on custom-designed electronics, and the High Level Trigger (HLT), a streamlined version of the CMS reconstruction and analysis software running on a computer farm. The software-base HLT requires a trade-…
