Small-strip Thin Gap Chambers Research Articles

The ATLAS experiment at the CERN Large Hadron Collider: a description of the detector configuration for Run 3

The ATLAS detector is installed in its experimental cavern at Point 1 of the CERN Large Hadron Collider. During Run 2 of the LHC, a luminosity of ℒ = 2 × 1034 cm-2 s-1 was routinely achieved at the start of fills, twice the design luminosity. For Run 3, accelerator improvements, notably luminosity levelling, allow sustained running at an instantaneous luminosity of ℒ = 2 × 1034 cm-2 s-1, with an average of up to 60 interactions per bunch crossing. The ATLAS detector has been upgraded to recover Run 1 single-lepton trigger thresholds while operating comfortably under Run 3 sustained pileup conditions. A fourth pixel layer 3.3 cm from the beam axis was added before Run 2 to improve vertex reconstruction and b-tagging performance. New Liquid Argon Calorimeter digital trigger electronics, with corresponding upgrades to the Trigger and Data Acquisition system, take advantage of a factor of 10 finer granularity to improve triggering on electrons, photons, taus, and hadronic signatures through increased pileup rejection. The inner muon endcap wheels were replaced by New Small Wheels with Micromegas and small-strip Thin Gap Chamber detectors, providing both precision tracking and Level-1 Muon trigger functionality. Trigger coverage of the inner barrel muon layer near one endcap region was augmented with modules integrating new thin-gap resistive plate chambers and smaller-diameter drift-tube chambers. Tile Calorimeter scintillation counters were added to improve electron energy resolution and background rejection. Upgrades to Minimum Bias Trigger Scintillators and Forward Detectors improve luminosity monitoring and enable total proton-proton cross section, diffractive physics, and heavy ion measurements. These upgrades are all compatible with operation in the much harsher environment anticipated after the High-Luminosity upgrade of the LHC and are the first steps towards preparing ATLAS for the High-Luminosity upgrade of the LHC. This paper describes the Run 3 configuration of the ATLAS detector.

ATLAS New Small Wheel performance studies after first year of operation

After successfully completing Phase I upgrades during LHC Long Shutdown 2, the ATLAS detector is back in operation with several upgrades implemented. The most important and challenging upgrade is in the Muon Spectrometer, where the two inner forward muon stations have been replaced with the New Small Wheels (NSWs) system featuring two entirely new detector technologies: small strip Thin Gap Chambers (sTGC) and the resistive Micromegas (MM). After massive construction, testing and installation work in ATLAS, the two NSWs end-caps have now been in operation for about a year in the experiment, participating in the muon spectrometer tracking system and muon trigger system. A huge effort has gone into the operation of the new data acquisition system, as well as the implementation of a new processing chain within the muon software framework. Tracking is performed with full consideration of the absolute alignment of each individual detector module by the ATLAS Muon Spectrometer optical alignment system. All the deviations from the nominal geometry of all the constituent elements of each sTGC and MM module are accounted for through the modelling of the real chamber geometry reconstructed from the information of the construction databases. After an overview of the strategies adopted for the simulations and reconstruction, the studies on the performance of the NSW system in its first year of operation with LHC Run3 data will be reported.

High rate studies of the ATLAS sTGC detector and optimization of the filter circuit on the input of the front-end amplifier

The Large Hadron Collider (LHC) at CERN is expected to be upgraded to the High-Luminosity LHC (HL-LHC) by 2029 and achieve instantaneous luminosity around 5–7.5 × 1034 cm-2 s-1. This represents a more than 3–4 fold increase in the instantaneous luminosity compared to what has been achieved in Run 2. The New Small Wheel (NSW) upgrade is designed to be able to operate efficiently in this high background rate environment. In this article, we summarize multiple performance studies of the small-strip Thin Gap Chamber (sTGC) at high rate using nearly final front-end electronics. We demonstrate that the efficiency versus rate distribution can be well described by an exponential decay with electronics dead-time being the primary cause of loss of efficiency at high rate. We then demonstrate several methods that can decrease the electronics dead-time and therefore minimize efficiency loss. One such method is to install either a pi-network input filter or pull-up resistor to minimize the charge input into the amplifier. We optimized the pi-network capacitance and pull-up resistor resistance using the results from our measurements. The results shown here were not only critical to finalizing the components on the front-end board, but also are critical for setting the optimal operating parameters of the sTGC detector and electronics in the ATLAS cavern.

Validation of the New Small Wheel Micromegas sectors for the phase 1 upgrade of the muon forward spectrometer of the ATLAS experiment at CERN

The ATLAS experiment is currently upgrading the first muon station in the high-rapidity region with the New Small Wheels (NSW), based on large-size resistive Micromegas (MM) technology and small-strip Thin Gap Chambers (sTGC). The NSW system is going to be installed in the ATLAS underground cavern during the LHC long shutdown 2 (2021) to enter in operation for Run3 (starting in the first months of 2022). 128 Micromegas quadruplets, each composed by four measurement layers two to three square meters in size, are needed to build the two New Small Wheels, covering a total active area of about 1280 m2. The construction of all MM modules, carried out in France, Germany, Italy, Russia and Greece, is completed. Their mechanical integration into sectors, the installation of on-detector services and electronics, for the first NSW is also completed, along with all validation and acceptance tests. The preparation of the second NSW is very well advanced. The advanced status of the project, in view of the imminent installation of the two NSW in ATLAS by the fall of 2021 will be reported. Micromegas detector construction and integration into sectors is presented, together with results obtained with cosmic rays data during the validation tests and the impressive steps of the wheel assembly completion.

Performance studies of Micromegas electronics in a high radiation environment at the CERN Gamma Irradiation Facility (GIF++)

The ATLAS experiment at CERN undergoes a series of upgrades, in line with the upgrades (Phase-I and Phase-II) of the Large Hadron Collider (LHC), to cope with the steadily increasing instantaneous luminosity that ultimately is expected to reach 7.5×1034cm−2 s−1 at the High Luminosity LHC (HL-LHC) era. The most challenging upgrade project of the ATLAS experiment concerns its Muon Spectrometer’s inner wheel-shaped detection stations (Small Wheels) located close to and on either side of the pp beams’ interaction point. Another type of detection system (New Small Wheels) replaced the two Small Wheels so that the ATLAS maintains its performance while preserving the acceptance of critical physics signatures under the harsh conditions of higher data and radiation rates (up to 25kHz/cm2 at the HL-LHC accelerator). The NSWs are a complex detection system (each wheel comprises 2.4x106 readout channels)that employ two novel micro-pattern gaseous detector technologies, the Micromesh Gaseous Structure (Micromegas, MM) and the small strip Thin Gap Chambers (sTGCs), mainly to improve the trigger performance and to provide precise spatial measurements. New electronic boards residing on the detectors were designed and manufactured, hosting high radiation and magnetic field tolerant custom-made ASICs.This paper presents extensive tests carried out at the new CERN Gamma Irradiation Facility (GIF++) by combining a muon beam (of 12kHz) with a 137Cesium radiation source of adjustable rate (up to ten times the expected rate at the HL-LHC conditions), to assess the performance of the Micromegas chambers and their readout electronics. Data from NSW Micromegas modules of different detection areas, having different positions on the wheels, operating with different high voltage and filling gas have been read out and analyzed by placing the electronics on PCBs located at various distances from the pp beam pipe. The spatial resolution of the precision coordinate is found to be well below the required 100μm, and the excellent alignment of the precision layers has been verified. Results confirm that all types of Micromegas modules tested have a linear response up to a rate around four times the expected at HL-LHC.

Construction and test of the SM1 type Micromegas chambers for the upgrade of the ATLAS forward muon spectrometer

Large-size Resistive Micromegas have been chosen for the upgrade of the forward muon spectrometer of the ATLAS experiment, the New Small Wheel project. These chambers, together with small-strip Thin Gap Chambers (sTGC), allow reconstruction of high-momentum muon tracks in a high-radiation environment and provide a robust low-threshold single-muon trigger. A collaboration of seven INFN units built 32 SM1 type chambers, corresponding to one fourth of the total number needed for this upgrade. Each SM1 chamber has a surface of approximately 2 m2 and four sensitive layers. The production was shared among five INFN construction sites and it was completed in fall 2020. The construction methods, as well as the results of the quality tests done on components of the detector and on the assembled chambers, are reported in the present paper.

Micromegas sectors for the ATLAS muon upgrade, towards the installation of the New Small Wheel in 2021

The ATLAS experiment is currently upgrading the first muon station in the high-rapidity region with the construction of new detector structures, named New Small Wheels (NSW), based on large-size multi-gap resistive strip Micromegas (MM) technology and small-strip Thin Gap Chambers (sTGC). The NSW is being installed in the ATLAS underground cavern during the on-going LHC long shutdown 2 to enter operation for run 3. 128 Micromegas quadruplets, each of which provides four measurements of a particle track, are needed to build the two New Small Wheels, covering a total active area of about 1280 m2. The construction of all MM modules, carried out in France, Germany, Italy, Russia and Greece, is completed. Their mechanical integration into sectors, and the installation of on-detector services and electronics for the first NSW is also completed, along with all validation and acceptance tests. The preparation of the second NSW is well advanced. The advanced status of the project, in view of the imminent installation of the two NSW in ATLAS by the 2021 is reported. The integration workflow of Micromegas detectors into sectors is described with focus on cosmic rays results of the final validation tests.

Ultra-low jitter clock distribution for the trigger electronics of the New Small Wheel for the ATLAS experiment

The Large Hadron Collider (LHC) at CERN plans to have a series of upgrades to increase its instantaneous luminosity to 7.5 × 1034 cm−2 s−1. The increased luminosity drastically impacts the ATLAS trigger and readout data rates. The inner-most station of the ATLAS muon spectrometer, the so-called Small Wheels is being replaced with a New Small Wheel (NSW) system, consisting of Micromegas and small-strip Thin Gap Chambers (sTGC) detectors. The on-detector radiation levels required radiation tolerant electronics. The lower radiation levels on the rim of the NSW allowed utilizing commercial electronic chips, such as Field Programmable Gate Arrays (FPGAs), in the trigger chain of the sTGC detectors. Those FPGAs require an ultra-low jitter clock for the proper operation of their Gigabit transceivers (4.8 Gb/s serial links). The initial design was based on a clock provided by a radiation tolerant ASIC designed at CERN, but due to its intrinsic jitter and consequent marginal error rate on the transmission lines, a different approach had to be chosen. An additional clock source based on commercial jitter cleaners, fanout chips and optical transmitters driving dedicated fibers was built. The new scheme provides 64 low-jitter clocks (32 main and 32 redundant) from the radiation-protected area (USA15) to the trigger electronics over 60 m of OM3 fiber.

Design and testing of an sTGC ASIC interface board for the ATLAS New Small Wheel upgrade

The ATLAS experiment will replace the present small wheel (SW) detector with a new small wheel detector (NSW) aiming to improve the performance of muon triggering and precision tracking in the endcap region at the high-luminosity LHC. small-strip thin gap chamber (sTGC) is one of the two new detector technologies used in this upgrade. A few custom-designed ASICs are needed for the sTGC detector. An sTGC ASIC interface board is designed to test ASIC-to-ASIC communication and to validate the functionality of the entire system. A test platform with the final readout system is set up and the whole sTGC readout chain is demonstrated for the first time. Key parameters in the readout chain are discussed and the results are shown.

Construction and operation of large scale Micromegas detectors for the ATLAS Muon upgrade

After the forthcoming upgrade of the LHC accelerator at CERN, its luminosity will increase up to 7.5 × 1034 cm−2s−1. That will raise the readout rates and the background data to unmanageable levels for the existing ATLAS muon spectrometer. The ATLAS collaboration has proposed to replace the present small wheel muon detector with the New Small Wheel (NSW) to surpass those limitations. The new wheels consist of Micromegas (MM) and small-strip Thin Gap Chambers (sTGC). The first technology aims for precision tracking, and the last one for trigger purposes. Each wheel will be equipped with eight small and eight large sectors, while each sector will have a double MM wedge surrounded by sTGC wedges. The MM detectors for the NSW will be the largest developed Micro Pattern Gaseous Detector (MPGD) as they will cover an area up to 1280 m2. During detectors’ manufacture have been used various custom materials (PCBs, mesh) and innovative construction techniques. This paper describes the MM drift panels production at Aristotle University of Thessaloniki laboratory. Then will be presented resolution results of the MM detectors with cosmic-ray tests at CERN facilities.

The Micromegas Surface Commissioning For the ATLAS New Small Wheel

In order to cope with the required precision tracking and trigger capabilities from Run III onward in the ATLAS experiment, the innermost layer of the Muon Spectrometer end-cap (Small Wheels) will be upgraded. Each of the two New Small Wheels (NSW) will be equipped with eight layers of MicroMegas (MM) detectors and eight layers of small-strip Thin Gap Chambers (sTGC), both arranged in two quadruplets. MM detectors of large size (up to 3m2) will be employed for the first time in HEP experiments.Four different types of MM quadruplet modules (SM1, SM2, LM1, LM2), built by different Institutes, compose the NSW. The modules are then sent to CERN, integrated into double wedges (DW), tested and sent for commissioning on the wheel itself. At the commissioning stage the MM double wedges along with the sTGC wedges are assembled together into sectors which are then installed and tested on the wheel. Each wheel comprises 8 small (made of SM1 and SM2 modules) and 8 large (made of LM1 and LM2 modules) sectors, in order to provide full coverage of the end caps.The first of the two wheels (NSW-A) has been fully commissioned, installed in ATLAS and the first tests are currently ongoing. The second wheel (NSW-C) is currently under commissioning and is expected to be ready by October this year.

The STAR detector upgrades for the BES II and beyond physics program

The Beam Energy Scan program (BES) at the Relativistic Heavy Ion Collider (RHIC) is dedicated to explore the Quantum Chromodynamics (QCD) phase diagram and to search for the critical point of the QCD phase transition. The results from the BES phase I program show hints of a first-order phase transition in the QCD phase diagram and the turn-off of the characteristic signatures of the quark gluon plasma at low collision energies, sNN<20GeV. Three upgrades of the STAR detector, the inner Time Projection Chamber, the Event Plane Detector, and the endcap Time Of Flight, provide unique opportunities to further investigate the nature of the QCD phase diagram during the BES phase II program (BES II), which covers the sNN from 7.7 to 19.6 GeV in the collider mode and from 3 to 7.7 GeV in the fixed-target mode. Beyond the BES II, the STAR Collaboration currently designs, constructs, and installs a suite of new detectors in the forward rapidity region (2.5 <η < 4) over the next two years, enabling a program of novel measurements in p+p, p+A and A+A collisions. This extension of STAR's kinematic reach will allow a detailed study of cold QCD physics at both very high and very low partonic momentum fraction. The new subdetectors to be installed comprise a Forward Calorimeter System, with electromagnetic and hadronic calorimetry. As well as a Forward Tracking System, which consists of 3 layers of silicon mini-strip detectors and 4 layers of small-strip Thin Gap Chambers. In this presentation, the detailed description on the STAR detector upgrades for the BES II and beyond, their performance, as well as the future physics opportunities, will be given.

New Small Wheels for the ATLAS Muon Spectrometer

The ATLAS collaboration at Large Hadron Collider (LHC) has chosen the Large size multi-gap resistive strips Micromegas (MM) technology along with the small-strip Thin Gap Chambers (sTGC) for the High Luminosity (HL) upgrade of the first muon station in the high-rapidity region, the so called New Small Wheel (NSW) project. The NSW is expected to be installed in the ATLAS underground cavern in the current long shutdown. After the R&D, design and prototyping phase, series production MM and sTGC chambers are being constructed. At CERN, the final validation and integration of the modules in sectors composing the wheel is well advanced. The achievement of the requirements for these detectors revealed to be even more challenging than expected, when scaling from the small prototypes to the large dimensions. In this document the main challenges of the project, the adopted solutions and performance results are presented.

The development of the Front-End Boards for the small-strip Thin Gap Chambers detector system of the ATLAS Muon New Small Wheel upgrade

The ATLAS experiment at CERN is scheduled to replace the innermost station of its Muon Spectrometer in the forward region during its Phase-I upgrade in order to enhance the capabilities on triggering and tracking of high transverse momentum muons towards high luminosity LHC runs. The New Small Wheel (NSW), a completely new detector system to be built, is composed of two novel gaseous detectors: Micro-mesh Gaseous Structure (Micromegas) and the small-strip Thin Gap Chamber (sTGC). The sTGC sub-system is the primary trigger detector. It will be equipped with radiation-tolerant, low-latency electronics for reading out over 400,000 channels to identify the bunch crossing time of proton-proton collisions spaced by 25 ns, as well as to collect fine strip charge information for the charged track reconstruction. In this paper, we present the design and development of a set of Front-End Boards (FEBs) for the sTGC detector system. The major challenges in the design will be discussed. These include the accommodation of a few hundred readout channels per single board in a very constrained space, a tight requirement for the Electrostatic Discharge (ESD) protection of 130 nm ASICs, and customized analog input circuits to handle the high rate and high charge signals from the sTGC detectors. Moreover, the FEBs have to incorporate a few hundred parallel inter-chip links at 320 Mbps and several low-latency serial links operating at 4.8 Gbps for the Level-1 and trigger data readout. The characterization of the FEBs performance, both off-detector and on-detector, will be shown.

Micromegas chambers for the ATLAS New Small Wheel upgrade

The ATLAS collaboration at LHC has chosen the resistive Micromegas technology, along with the small-strip Thin Gap Chambers (sTGC), for the high luminosity upgrade of the first muon station in the high-rapidity region, the so called New Small Wheel (NSW) project. After the R&D, design and prototyping phase, the series production Micromegas quadruplets are being constructed at the involved construction sites in France, Germany, Italy, Russia and Greece. At CERN, the final validation and the integration of the modules in Sectors are in progress. The installation of the first NSW, the NSW-A is foreseen for the LHC long shutdown in 2020. The construction of the four types of large size quadruplets, all having trapezoidal shapes with surface areas between 2 and 3 m2, will be reviewed. The achievement of the requirements for these detectors revealed to be even more challenging than expected, when scaling from the small prototypes to the large dimensions. The encountered problems will be described, to a large extent common to other micro-pattern gaseous detectors, along with the adopted solutions. Final quality assessment and validation results on the achieved mechanical precision, on the High-Voltage stability during operation with and without irradiation will be reviewed together with the most relevant steps and results of the modules integration into sectors.

The sTGC prototyping and performance test for the STAR forward upgrade

The STAR experiment at RHIC is implementing a new Forward Tracking System (FTS) which consists of a Forward Silicon Tracker (FST) and a Forward sTGC Tracker (FTT). The small-strip Thin Gap Chambers (sTGC) at STAR are designed to provide precision position measurements of about 100 μm for charged particles at high luminosity, covering the forward rapidity region (2.5 < η < 4). The extended rapidity coverage in particle tracking enables lots of physics opportunities in pp, pA and AA programs beyond 2021 at STAR . Two size sTGC prototypes have been designed and produced at Shandong University. The final designation will be finished by Feb.2020. In this paper, the sTGC prototype research and development details and some performance test results, such as detection efficiency, will be presented. Current status and future plan of the FTT upgrade will also be discussed.

Small-strip thin gap chambers for the muon spectrometer upgrade of the ATLAS experiment

The instantaneous luminosity of the Large Hadron Collider at CERN will be increased by about a factor of five with respect to the design value after the extensive upgrade program over the coming decade. In order to cope with the increasing luminosity, the ATLAS experiment is being upgraded as well. The largest phase-1 upgrade project for the ATLAS Muon System is the replacement of the present first station in the forward regions with the New Small Wheels (NSWs) during the long-LHC shutdown in 2019-2021. The NSWs are based on two detector technologies: Micromegas (MM) and small-strip TGC (sTGC), the later arranged in two quadruplets, each consisting of 8 layers. To retain the good precision tracking and trigger capabilities in the high background environment of the high luminosity LHC, each sTGC plane must achieve a spatial resolution better than 100 μm. It will allow to reconstruct tracks with an angular resolution of approximately 1 mrad. The sTGC design, performance, construction and integration status are discussed, along with results from tests of the chambers with nearly final electronics with beams, cosmic rays and high-intensity radiation sources.

The Micromegas chambers for the ATLAS New Small Wheel upgrade

The ATLAS collaboration at the LHC has chosen the resistive Micromegas (MM) technology, along with the small-strip Thin Gap Chambers (sTGC), for the high luminosity upgrade of the first muon station in the high-rapidity region, the so called New Small Wheel (NSW) project. After the R&D, design and prototyping phase, the first series production Micromegas quadruplets are being constructed at the involved construction sites in France, Germany, Italy, Russia and Greece. At CERN, the final validation and the integration of the modules in Sectors are in progress. These are big steps forward for the installation of the NSW foreseen for the LHC long shutdown in 2019 and 2020. The construction of the four types of large size quadruplets, all having trapezoidal shapes with surface areas between 2 and 3 m2, will be reviewed. Achieving the requirements for these detectors has proven to be even more challenging than expected, when scaling from the small prototypes to large dimensions. We will describe the encountered problems, to a large extent common to other micro-pattern gaseous detectors, and the adopted solutions. Final quality assessment of the High-Voltage stability of the modules, with and without irradiation, will be presented together with the most relevant steps and results.

Precision survey of the readout strips of small-strip Thin Gap Chambers using X-rays for the muon spectrometer upgrade of the ATLAS experiment

The instantaneous luminosity of the Large Hadron Collider (LHC) will be increased by a factor of 5 to 7 after a series of upgrades of the CERN accelerator complex. In anticipation to the increased collision rate at the interaction point, the muon end-cap inner station of the ATLAS detector will be replaced with the so-called New Small Wheels (NSWs) during the LHC shutdown of 2019/2020. The NSWs combine the Micromegas and small-strip Thin Gap Chambers (sTGC) technologies. The sTGC detector modules are arranged in trapezoid wedges of 4 detector planes with total active areas varying between 3 and 5 m2 per plane. Over 1000 azimuthal cathode strips are read out on each plane for precision muon trajectory measurements. The positioning of individual strips must be known to within 100 microns to satisfy the performance targets of this ATLAS upgrade. Non-conformities of the sTGC strip-pattern are therefore measured on finished wedges using an X-ray gun precisely positioned at reference points. The working principles and the spatial resolution measurement of this technique are presented.

Test Beam Results and Performance Studies of ATLAS Micromegas Production Modules

The LHC at CERN plans to have a series of upgrades to increase its instantaneous luminosity up to 7.5 × 1034 cm−2·s−1. The ATLAS experiment will upgrade its inner end-cap muon chambers to cope with the increased collision rate expected from the High-Luminosity-LHC. This project, called New Small Wheel, includes resistive Micromegas chambers together with small-strip Thin Gap Chambers, forming a system of ˜2.4 million readout channels in total. This is the first time that Micromegas detectors are built in such a large scale. In total, 128 Micromegas modules up to 3 m2 in size, will be produced in different sites spread across Europe, targetting for an installation at the end of the Long Shutdown 2 of the LHC. One of the first series modules, equipped with a prototype of the final front-end electronics based on the VMM chip, was tested in a muon/pion beam at the H8 beam line of SPS at CERN during the summer of 2018. We present the test setup and performance results, namely effciency and resolution, for perpendicular and inclined tracks. These studies were focused on determining the high voltage working point of the ATLAS Micromegas detectors. Studies with several gas mixtures were also carried out and will be presented.