Silicon Strip Tracker Research Articles

Development of a MAPS-based upstream tracker for the LHCb upgrade II

The LHCb Upstream Tracker is a silicon strip tracking detector that started operation in the Run 3 of the LHC. To meet the requirements imposed by high occupancy and data rate at the HL-LHC, a new Upstream Pixel (UP) tracker is proposed for LHCb Upgrade II based on CMOS pixel sensors. A preliminary detector layout is presented. The design of a sensor in a 55 nm high-voltage CMOS technology is introduced and further development is in process. Performance studies of UP with simulation are also ongoing.

Performance of the Fermi-LAT silicon strip tracker after 14 years of operation

The Large Area Telescope (LAT) is the primary instrument onboard the Fermi Gamma-ray Space Telescope launched on June 11 2008. It is an imaging, wide field-of-view, gamma-ray telescope, covering the energy range from 30 MeV to more than 300 GeV. The LAT tracker is formed by silicon strip planes alternated with tungsten foils and is used to convert the incoming photon into an electron-positron pair and to measure its direction. Here we describe the performance of the LAT tracker, that has been constantly monitored using calibration and science data. In particular we show that, after almost 14 years of continuous operation in space, the fraction of defective channels is less than 0.5% while the readout noise increased less than 5%.

Heavy Flavor and Quarkonia Physics at sPHENIX

The sPHENIX detector, being constructed at BNL’s Relativistic Heavy Ion Collider (RHIC), will begin measuring a plethora of Heavy Flavor and Quarkonia observables with unprecedented statistics and kinematic reach at RHIC energies starting in 2023. This includes the largest recorded sample of b-flavored hadron decays from Heavy Ion collisions at RHIC, allowing for precise probes of the QGP using charm and beauty quarks. These measurements are enabled by the excellent vertexing of the MAPS-based micro-VerTeX detector (MVTX), timing of the INTermediate silicon strip Tracker (INTT), precision tracking by the Time Projection Chamber (TPC), and the ElectroMagnetic and Hadronic Calorimetry systems (EMCal and HCal, respectively), the latter of which is deployed for the first time at RHIC. The sPHENIX collaboration has created the reconstruction software stack as well as realistic data simulations, which allow for testing and optimization of the software and physics selections.

Status of the CMS silicon strip tracker

The CMS silicon strip tracker with its more than 15000 silicon modules and about 200 m2 of active silicon area will resume operation after three years of Long Shutdown 2 in the Spring of 2022. We present the status of the detector before the start of the LHC Run 3 data taking. The performance of the detector during the Run 2 data taking is presented including the signal-to-noise ratio, fraction of bad components in the detector, hit efficiency, and single hit resolution. We discuss projections of the detector performance during Run 3. In addition the change of detector parameters with increasing radiation damage is reviewed.

An overview of the trigger system at the CMS experiment

The trigger system of the Compact Muon Solenoid (CMS) experiment at CERN has been evolving continuously since the startup of the LHC. While the base of the current configuration will remain in use for the next LHC running period (Run 3 starting in 2022), new features and algorithms are already being developed to take care of higher data loads due to increasing LHC luminosity and pileup but also of new experimental signatures to be investigated, in particular, displaced decay vertices stemming from relatively long-lived particles created in proton-proton collisions. Beyond this period, the trigger system will undergo a major upgrade to prepare for the high-luminosity LHC (HL-LHC) operations, which will deliver a luminosity of 5–7.5 times the design value. It corresponds to 140-200 pileup events, defined as overlapping proton-proton interactions in the same or nearby bunch crossings. During HL-LHC, information from the silicon pixel and strip tracker will be available already for the Level-1 Trigger, detector granularity and pseudorapidity coverages will increase. Trigger rates will rise by a factor of about 7.5 both at Level-1 (to 750 kHz) and at the High Level Trigger (to 7.5 kHz) and the latency—the processing time available for arriving at the Level-1 trigger decision—will increase significantly from 3.8 μs to 12.5 μs, allowing for the use of more sophisticated algorithms at the Level-1 trigger.

The Phase-2 Upgrade of the Hardware Trigger of CMS at the LHC

The CMS experiment uses a two-level triggering system consisting of the Level-1, instrumented by custom-design hardware boards, and the High Level Trigger, a streamlined version of the offline reconstruction software running on a computer farm. The upgrade of the collider to the “High-Luminosity LHC”, which will deliver a luminosity of 5−7.5 × 1034 cm−2s−1, corresponding to 140–200 pileup events, also necessitates a complete upgrade of the trigger system to make optimal use of the data. An important difference from the present system will be the fact that after the upgrade, information from the silicon strip tracker will be available already for the Level-1 Trigger. This will allow CMS to use so-called “particle flow” objects, i.e. signals seen not only in one subdetector but put together from all available subdetectors, resulting in much sharper efficiency turn-on curves for trigger objects. Also, trigger rates will rise both at Level-1 (from 100 kHz to 750 kHz) and at the High-Level Trigger (from 1 kHz to 7.5 kHz). At the same time, more sophisticated algorithms will be available at Level-1. To make this possible, the latency—the processing time available for arriving at the Level-1 trigger decision—will increase significantly. Machine-learning techniques such as Boosted Decision Trees have already started to be implemented in the trigger electronics and will occupy a more important place in the future. The use of High-Level Synthesis (HLS) tools will allow physicists to formulate trigger requirements in a language closer to that of data analysis. To avoid missing unexpected signatures from New Physics, studies are underway to employ anomaly detection using autoencoders.

Prototyping of petalets for the Phase-II upgrade of the silicon strip tracking detector of the ATLAS experiment

In the high luminosity era of the Large Hadron Collider, the instantaneous luminosity is expected to reach unprecedented values, resulting in about 200 proton-proton interactions in a typical bunch crossing. To cope with the resultant increase in occupancy, bandwidth and radiation damage, the ATLAS Inner Detector will be replaced by an all-silicon system, the Inner Tracker (ITk). The ITk consists of a silicon pixel and a strip detector and exploits the concept of modularity. Prototyping and testing of various strip detector components has been carried out. This paper presents the developments and results obtained with reduced-size structures equivalent to those foreseen to be used in the forward region of the silicon strip detector. Referred to as petalets, these structures are built around a composite sandwich with embedded cooling pipes and electrical tapes for routing the signals and power. Detector modules built using electronic flex boards and silicon strip sensors are glued on both the front and back side surfaces of the carbon structure. Details are given on the assembly, testing and evaluation of several petalets. Measurement results of both mechanical and electrical quantities are shown. Moreover, an outlook is given for improved prototyping plans for large structures.

Study of the material of the ATLAS inner detector for Run 2 of the LHC

The ATLAS inner detector comprises three different sub-detectors: the pixel detector, the silicon strip tracker, and the transition-radiation drift-tube tracker. The Insertable B-Layer, a new innermost pixel layer, was installed during the shutdown period in 2014, together with modifications to the layout of the cables and support structures of the existing pixel detector. The material in the inner detector is studied with several methods, using a low-luminosity √s=13 TeV pp collision sample corresponding to around 2.0 nb−1 collected in 2015 with the ATLAS experiment at the LHC. In this paper, the material within the innermost barrel region is studied using reconstructed hadronic interaction and photon conversion vertices. For the forward rapidity region, the material is probed by a measurement of the efficiency with which single tracks reconstructed from pixel detector hits alone can be extended with hits on the track in the strip layers. The results of these studies have been taken into account in an improved description of the material in the ATLAS inner detector simulation, resulting in a reduction in the uncertainties associated with the charged-particle reconstruction efficiency determined from simulation.

Prototyping of hybrids and modules for the forward silicon strip tracking detector for the ATLAS Phase-II upgrade

For the High-Luminosity upgrade of the Large Hadron Collider an increased instantaneous luminosity of up to 7.5 ⋅ 1034 cm−2 s−1, leading to a total integrated luminosity of up to 3000 fb−1, is foreseen. The current silicon and transition radiation tracking detectors of the ATLAS experiment will be unable to cope with the increased track densities and radiation levels, and will need to be replaced. The new tracking detector will consist entirely of silicon pixel and strip detectors. In this paper, results on the development and tests of prototype components for the new silicon strip detector in the forward regions (end-caps) of the ATLAS detector are presented. Flex-printed readout boards with fast readout chips, referred to as hybrids, and silicon detector modules are investigated. The modules consist of a hybrid glued onto a silicon strip sensor. The channels on both are connected via wire-bonds for readout and powering. Measurements of important performance parameters and a comparison of two possible readout schemes are presented. In addition, the assembly procedure is described and recommendations for further prototyping are derived.

Beam test of CSES silicon strip detector module**Supported by the XXX Civil Space Programme

The silicon-strip tracker of the China Seismo-Electromagnetic Satellite (CSES) consists of two double-sided silicon strip detectors (DSSDs) which provide incident particle tracking information. A low-noise analog ASIC VA140 was used in this study for DSSD signal readout. A beam test on the DSSD module was performed at the Beijing Test Beam Facility of the Beijing Electron Positron Collider (BEPC) using a 400–800 MeV/c proton beam. The pedestal analysis results, RMSE noise, gain correction, and intensity distribution of incident particles of the DSSD module are presented.

Development and test of the CO2 evaporative cooling system for the LHCb UT Tracker Upgrade

The LHCb upgrade requires a new silicon strip tracker detector placed between the vertex locator and the magnet. The new detector will have improved performance in charged particle tracking and triggering. The front-end electronics will be in the active area, close to the sensors: this is a key feature driving the mechanical and cooling detector design, together with the requirement to make the sensors work below −5°C, to withstand radiation damage. The new design exploits a cooling system based on CO2 evaporation at temperatures around −25°C. The support structure for the sensor modules is a lightweight carbon fiber mechanical structure embedding a cooling pipe, designed to pass underneath the read-out ASICs, which are the main thermal power sources to be cooled down. Here a description of the detector will be given, with a main focus on the cooling system and on the progress done to its qualification.

Radiation hardness of two CMOS prototypes for the ATLAS HL-LHC upgrade project.

The LHC luminosity upgrade, known as the High Luminosity LHC (HL-LHC), will require the replacement of the existing silicon strip tracker and the transistion radiation tracker. Although a baseline design for this tracker exists the ATLAS collaboration and other non-ATLAS groups are exploring the feasibility of using CMOS Monolithic Active Pixel Sensors (MAPS) which would be arranged in a strip-like fashion and would take advantage of the service and support structure already being developed for the upgrade. Two test devices made with the AMS H35 process (a High voltage or HV CMOS process) have been subjected to various radiation environments and have performed well. The results of these tests are presented in this paper.

Performance of the LHCb tracking system in Run I of the LHC

The LHCb tracking system consists of a Vertex Locator around the interaction point, a tracking station with four layers of silicon strip detectors in front of the magnet, and three straw-tube and silicon strip tracking stations behind the magnet. This system allows reconstruction of charged particles with a high efficiency (>95% for particles with momentum p>5GeV) and excellent momentum resolution (0.5% for particles with p<20GeV). The high momentum resolution results in narrow mass peaks, leading to a high signal-to-background ratio in such key channels as Bs0→μμ. The excellent performance of the tracking system yields a decay time resolution of ~50fs, allowing to resolve the fast B0s oscillation with a mixing frequency of 17.7ps−1. Such a decay time resolution is an essential element in studies of time dependent CP violation. I present an overview of the track reconstruction in LHCb and its performance in Run I of the LHC. I highlight the challenges and improvements of the track reconstruction from Run II onward, including efforts to improve the timing of the online reconstruction and approaches to unify the online and offline reconstruction.

Silicon strip tracking detector development and prototyping for the Phase-II upgrade of the ATLAS experiment

In about ten years from now, the Phase-II upgrade of the LHC will be carried out. Due to increased luminosity, a severe radiation dose and high particle rates will occur for the experiments. In consequence, several detector components will have to be upgraded. In the ATLAS experiment, the current inner detector will be replaced by an all-silicon tracking detector with the goal of at least delivering the present detector performance also in the harsh Phase-II LHC conditions. This report presents the current planning and results from first prototype measurements of the upgrade silicon strip tracking detector.

Development of a Fast Cluster Finding self-seeded trigger demonstrator

The ABC 130 chip developed for the high luminosity LHC(HL-LHC) upgrade of the ATLAS silicon strip tracker implements a Fast Cluster Finder (FCF). The FCF is capable of reading out certain track cluster information serially with a clock rate up to 640 MHz, sufficient to output the location within the 40 MHz collision frequency. An external correlator circuit can be used to find the position coincidence of clusters at two adjacent layers of silicon sensor. The coincidence offset is related to the transverse momentum of the track, and therefore it provides information which may contribute to a Level-1 trigger decision. These circuit elements have been implemented in a sensor doublet configuration coupled to an FPGA which executes the correlator algorithm. Design and test results of this system are presented.

Double-sided super-module R&D for the ATLAS tracker at HL-LHC – A summary

Following successive upgrades of the CERN Large Hadron Collider (LHC) until approximately 2025, the High Luminosity LHC (HL-LHC) is expected to deliver pp collisions of centre-of-mass energy s=14TeV with a levelled peak luminosity in excess of 5×1034cm−2s−1 and an integrated luminosity of order 300fb−1 per year. The ATLAS Collaboration intends to replace the existing Inner Tracking Detector by a new tracker, with readout electronics as well as silicon pixel and strip sensor technology capable of maintaining the excellent mechanical and electrical performance of the existing tracker in the severe radiation and high collision rate environment of the HL-LHC. The super-module integration concept extends the proven design of the existing barrel silicon strip tracker to the HL-LHC, with double-sided stereo silicon micro-strip modules assembled into a low mass local support structure. The first phase of the Super-Module R&D programme has been successfully completed, demonstrating the feasibility of the Super-Module concept. A summary is made up of the key prototype mechanical and electrical results of the R&D, as well as a short perspective of future developments.

Characterization of the CBC2 readout ASIC for the CMS strip-tracker high-luminosity upgrade

The CMS Binary Chip 2 (CBC2) is a full-scale prototype ASIC developed for the front-end readout of the high-luminosity upgrade of the CMS silicon strip tracker. The 254-channel, 130 nm CMOS ASIC is designed for the binary readout of double-layer modules, and features cluster-width discrimination and coincidence logic for detecting high-PT track candidates. The chip was delivered in January 2013 and has since been bump-bonded to a dual-chip hybrid and extensively tested. The CBC2 is fully functional and working to specification: we present the result of electrical characterization of the chip, including gain, noise, threshold scan and power consumption, together with the performance of the stub finding logic. Finally we will outline the plan for future developments towards the production version.

Analysis on H spectral shape during the early 2012 SEPs with the PAMELA experiment

The satellite-borne PAMELA experiment has been continuously collecting data since 2006. This apparatus is designed to study charged particles in the cosmic radiation. The combination of a permanent magnet, a silicon strip tracker and a silicon-tungsten imaging calorimeter, and the redundancy of instrumentation allow very precise studies on the physics of cosmic rays in a wide energy range and with high statistics. This makes PAMELA a very suitable instrument for Solar Energetic Particle (SEP) observations. Not only does it span the energy range between the ground-based neutron monitor data and the observations of SEPs from space, but PAMELA also carries out the first direct measurements of the composition for the highest energy SEP events, including those causing Ground Level Enhancements (GLEs). In particular, PAMELA has registered many SEP events during solar cycle 24, offering unique opportunities to address the question of high-energy SEP origin. A preliminary analysis on proton spectra behaviour during this event is presented in this work.

Radiation damage in the diamond based beam condition monitors of the CMS experiment at the Large Hadron Collider (LHC) at CERN

The Beam Condition Monitor (BCM) of the CMS detector at the LHC is a protection device similar to the LHC Beam Loss Monitor system. While the electronics used is the same, poly-crystalline Chemical Vapor Deposition (pCVD) diamonds are used instead of ionization chambers as the BCM sensor material. The main purpose of the system is the protection of the silicon Pixel and Strip tracking detectors by inducing a beam dump, if the beam losses are too high in the CMS detector. By comparing the detector current with the instantaneous luminosity, the BCM detector efficiency can be monitored. The number of radiation-induced defects in the diamond, reduces the charge collection distance, and hence lowers the signal. The number of these induced defects can be simulated using the FLUKA Monte Carlo simulation. The cross-section for creating defects increases with decreasing energies of the impinging particles. This explains, why diamond sensors mounted close to heavy calorimeters experience more radiation damage, because of the high number of low energy neutrons in these regions. The signal decrease was stronger than expected from the number of simulated defects. Here polarization from trapped charge carriers in the defects is a likely candidate for explaining the difference, as suggested by Transient Current Technique (TCT) measurements. A single-crystalline (sCVD) diamond sensor shows a faster relative signal decrease than a pCVD sensor mounted at the same location. This is expected, since the relative increase in the number of defects is larger in sCVD than in pCVD sensors.

Silicon strip detectors for ATLAS at the HL-LHC upgrade

The present ATLAS silicon strip tracker (SCT) and transition radiation tracker (TRT) are to be replaced with new silicon strip detectors as part of the inner tracker system (ITK) for the Phase-II upgrade of the Large Hadron Collider, HL-LHC. We have carried out intensive R&D programs based on n+-on-p microstrip detectors to fabricate improved radiation hard strip detectors that can survive the radiation levels corresponding to the integrated luminosity of up to 3000fb−1. We describe the main specifications for this year's sensor fabrication and the related R&D results, followed by a description of the candidate schema for module integration.