Phase-2 Upgrade Research Articles

Measurement of the fractional radiation length of a pixel module for the CMS Phase-2 upgrade via the multiple scattering of positrons

High-luminosity particle collider experiments such as the ones planned at the High-Luminosity Large Hadron Collider require ever-greater vertexing precision of the tracking detectors, necessitating reductions in the material budget of the detectors. Traditionally, the fractional radiation length (x/X 0) of detectors is either estimated using known properties of the constituent materials, or measured in dedicated runs of the final detector. In this paper, we present a method of direct measurement of the material budget of a CMS prototype module designed for the Phase-2 upgrade of the CMS detector using a 40–65 MeV positron beam. A total of 630 million events were collected at the Paul Scherrer Institut PiE1 experimental area using a three-plane telescope consisting of the prototype module as the central plane, surrounded by two MALTA monolithic pixel detectors. Fractional radiation lengths were extracted from scattering angle distributions using the Highland approximation for multiple scattering. A statistical technique recovered runs suffering from trigger desynchronisation, and several corrections were introduced to compensate for local inefficiencies related to geometric and beam shape constraints. Two regions of the module were surveyed and yielded average x/X 0 values of (0.72 ± 0.05)% and (0.95 ± 0.09)%, which are compatible with empirical estimates for these regions computed from known material properties of 0.753% and 0.892%, respectively. Two types of higher-granularity maps of the fractional radiation length were produced, subdivided either into rectangular regions of uniform size, or polygonal-shaped regions of uniform material composition. The results bode well for the CMS Phase-2 upgrade modules, which will play a key role in the minimisation of the material of the upgraded detector.

Production and test of BI-RPC detectors for ATLAS Phase-2 upgrade

The current Resistive Plate Chamber (RPC) system is undergoing a major upgrade (ATL (2017)), consisting in the installation of approximately 1000 RPC detector units in the innermost barrel layer of the ATLAS Muon Spectrometer. The goal of the project is to increase the detector coverage, currently limited to approximately 80%, and improve the trigger robustness and efficiency. The production of the gas volumes takes place in Italy, in Germany and China, while the readout panels in Cosenza (Italy) and Hefei (China). The Italian collaboration is taking care of the construction and test of the chambers located in the large sectors of the ATLAS barrel (BIL). Here we present the state of the art of the production, certification and logistics related to all the components produced at the Italian sites, as well as the assembly line and characterization of the BIL chambers at CERN with cosmic rays. The certification results of the components produced are analyzed and discussed.

Beam test performance studies of CMS Phase-2 Outer Tracker module prototypes

A new tracking detector will be installed as part of the Phase-2 upgrade of the CMS detector for the high-luminosity LHC era. This tracking detector includes the Inner Tracker, equipped with silicon pixel sensor modules, and the Outer Tracker, consisting of modules with two parallel stacked silicon sensors. The Outer Tracker front-end ASICs will be able to correlate hits from charged particles in these two sensors to perform on-module discrimination of transverse momenta (p T). The p T information is generated at a frequency of 40 MHz and will be used in the Level-1 trigger decision of CMS. Prototypes of the so-called 2S modules were tested at the Test Beam Facility at DESY Hamburg between 2019 and 2020. These modules use the final front-end ASIC, the CMS Binary Chip (CBC), and for the first time the Concentrator Integrated Circuit (CIC), optical readout and on-module power conversion. In total, seven modules were tested, one of which was assembled with sensors irradiated with protons. An important aspect was to show that it is possible to read out modules synchronously. A cluster hit efficiency of about 99.75 % was achieved for all modules. The CBC p T discrimination mechanism has been verified to work together with the CIC and optical readout. The measured module performance meets the requirements for operation in the upgraded CMS tracking detector.

R&D of a timing measurement ASIC for possible HL-LHC upgrade

The Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) at CERN will undergo a major upgrade for the High Luminosity phase of the LHC (HL-LHC), which is expected to start in 2029 [1]. In addition to improving the detector rate capabilities and performance at increased higher luminosity, precision timing measurements are added to mitigate pile-up effects. The timing detector currently under construction covers pseudo-rapidity up to η=3[2] . A possible pathway for further improvements is the extension of timing capabilities to cover the full tracker acceptance up to η=4. Low Gain Avalanche Detectors (LGAD) pixels have been shown to be a suitable candidate for replacing a part of the pixel detector end-caps during a future Long Shutdown or Year-End Technical Stop of the LHC. Here, we present preliminary results of our design efforts towards a readout Application-specific integrated circuit (ASIC) capable of operating with LGAD pixel sensors [3]. The first results of the modeling of a part of the ASIC are demonstrated.

RD53 pixel chips for the ATLAS and CMS Phase-2 upgrades at HL-LHC

The Phase-2 upgrades at the High-Luminosity LHC of ATLAS and CMS experiments at CERN will require a new tracker with readout electronics operating in extremely harsh radiation environment (1 Grad), high hit rate (3.5 GHz/cm2) and high data rate readout (5 Gb/s). The RD53 collaboration is a joint effort between the ATLAS and CMS to qualify the chosen 65 nm CMOS technology in high radiation environment and develop the pixel readout chips of both experiments. After a half-scale demonstrator (RD53A) and full scale prototypes of the two ASICs (RD53B-ATLAS and RD53B-CMS), largely used by the two communities to characterize 3D and planar sensors, RD53 developed and submitted to foundry in 2023 the production chips. A general overview of the chip architecture will be described.

First results from the RD53 ATLAS pixel production readout ASIC (ITkPixV2) for HL-LHC

The Phase-2 upgrades of ATLAS and CMS for the High-Luminosity LHC (HL-LHC), require a new tracker with robust readout electronics capable of withstanding extreme radiation (1 Grad), a high hit rate (3 GHz/cm2), and a high data rate readout (5 Gb/s). In a joint effort between ATLAS and CMS, pixel detector readout chips have been designed by the RD53 collaboration in 65 nm CMOS technology. Based on a half-sized demonstrator (RD53A), two chip variants were designed for ATLAS and CMS, respectively. The ATLAS pre-production readout chip, ITkPixV1, was characterised in detail, and informed by the results, the final ATLAS pixel readout chip, ITkPixV2, has been designed, submitted, and the first wafers were received in July 2023. This contribution provides an overview of the characterisation measurements performed on the ITkPixV2 chip so far, focusing on bench-top testing of chip functionality, and first results of X-ray irradiation studies to assess the radiation tolerance of the chip.

Assembly and testing of 2S module prototypes for the CMS Phase-2 outer tracker upgrade

The HL-LHC necessitates a Phase-2 upgrade for the CMS detector, which includes the complete replacement of the existing tracker. The new Outer Tracker incorporates two types of silicon module, 2S and PS, based on an innovative transverse momentum (pT) discrimination idea. By using these modules, the information from the tracker will be sent to the Level-1 (L1) trigger for the first time. They will identify charged particles with pT > 2 GeV, helping to reduce the data sent to the L1 trigger. This paper offers a comprehensive overview of the 2S module prototyping process, which include the precise assembly and testing procedures to ensure their performance and quality before integration into the Outer Tracker. Additionally, to assess the performance of a 2S module in beam, the data from a DESY test beam is reconstructed and analyzed using the Corryvreckan offline reconstruction framework. The results demonstrate agreement to within 1% with those obtained using the EUTelescope framework.

Commissioning of the test system for PS and 2S hybrids for the Phase-2 Upgrade ofthe CMS Outer Tracker

The Phase-2 Upgrade [1] of the CMS Outer Tracker [2] requires the production of 7608 Strip-Strip (2S) and 5592 Pixel-Strip (PS) modules, altogether incorporating 45 192 hybrid circuits of 15 design variants. The module design makes the potential repairs impractical; therefore, performing production-scale testing of the hybrids is essential. Accordingly, a scalable, crate-based test system was designed and manufactured, allowing for parallel, high-throughput testing. To reproduce the operating conditions, the system was integrated within a climate chamber, which required the development of a remote control interface and the calibration of thermal cycles. The results and lessons learned from the test system integration and commissioning will be presented.

Hybrid designs and kick-off batch production experience for the CMS Phase-2 Upgrade

The CMS Tracker Phase-2 Upgrade requires the production of new sensor modules to cope with the requirements of the HL-LHC. The two main building blocks of the Outer Tracker are the Strip-Strip and Pixel-Strip modules. All-together 47'520 hybrid circuits will be produced to construct 8'000 Strip-Strip and 5'880 Pixel-Strip modules. The circuit designs for the mass production were fine-tuned and kick-off batches were manufactured to verify the latest changes in the designs before the series production. This contribution focuses on lessons learned from the prototyping stage, design optimization details for the mass production as well as test results and production yield from the kick-off batches.

The upgrade of the CMS muon system for the high luminosity LHC

The muon system of the CMS experiment is expected to upgrade all of its subdetectors for the Phase-2 of the Large Hadron Collider (LHC) that will begin in 2029. The upgrade plans for drift tubes (DTs), cathode strip chambers (CSCs) and resistive place chambers (RPCs) include a new electronics for better performance in high background rate conditions and to sustain the large radiation dose delivered by the high-luminosity LHC (HL-LHC). Two new RPC stations will also be installed to complement CSCs in the forward region 1.8 < |η| < 2.4, while three stations of triple-GEM (gas electron multiplier) detectors will complement CSCs in the region 1.5 < |η| < 2.4 and extend the CMS muon system coverage to the very forward pseudorapidity region 2.4 < |η| < 2.8. We present the goals and status of the CMS muon system upgrade including the performance of the early Phase-2 upgrades demonstrated in Run 3 with proton-proton collisions, the performance validation of the new detectors in test beams and the mass production status of the new stations.

The k4Clue package: Empowering future collider experiments with the CLUE algorithm

High granularity calorimeters have become increasingly crucial in modern particle physics experiments, and their importance is set to grow even further in the future. The CLUstering of Energy (CLUE) algorithm has shown excellent performance in clustering calorimeter hits in the High Granularity Calorimeter (HGCAL) developed for the Phase-2 upgrade of the CMS experiment. In this paper, the suitability of the CLUE algorithm for future collider experiments has been investigated and its capabilities tested outside the HGCAL reconstruction software. To this end, a new package, k4Clue, was developed which is now fully integrated into the Gaudi software framework and supports the EDM4hep data format for inputs and outputs. The performance of CLUE was demonstrated in three detectors for future colliders: CLICdet for the CLIC accelerator, CLD for the FCC-ee collider and a second calorimeter based on Noble Liquid technology also proposed for FCC-ee. Excellent reconstruction performance was observed for single photon events, even in the presence of noise, and the results are compatible with the performance of the algorithms used currently as the baseline for shower reconstruction in future e+e−-colliders. Moreover, CLUE demonstrates impressive timing capabilities, outperforming the current baseline algorithms and this advantage remains consistent regardless of the number of input hits. This work highlights the adaptability and versatility of the CLUE algorithm for a wide range of experiments and detectors and the algorithm’s potential for future high-energy physics experiments beyond CMS.

Reconstructing jets in the Phase-2 upgrade of the CMS Level-1 Trigger with a seeded cone algorithm

The Phase-2 Upgrade of the CMS Level-1 Trigger (L1T) will reconstruct particles using the Particle Flow algorithm, connecting information from the tracker, muon, and calorimeter detectors, and enabling fine-grained reconstruction of high level physics objects like jets. We have developed a jet reconstruction algorithm using a cone centred on an energetic seed from these Particle Flow candidates. The implementation is designed to find up to 16 jets in each Xilinx Ultrascale+ FPGA, with a latency of less than 1 µs, and event throughput of 6.7 MHz to fit within the L1T system constraints. Pipelined processing enables reconstruction of jet collections with different cone sizes for little additional resource cost. The design of the algorithm also provides a platform for additional computation using the jet constituents, such as jet tagging using neural networks. We will describe the implementation, its jet reconstruction performance, computational metrics, and the developments towards jet tagging.

Overview of the HL-LHC Upgrade for the CMS Level-1 Trigger

The High-Luminosity LHC will open an unprecedented window on the weak-scale nature of the universe, providing high-precision measurements of the standard model as well as searches for new physics beyond the standard model. Such precision measurements and searches require informationrich datasets with a statistical power that matches the high-luminosity provided by the Phase-2 upgrade of the LHC. Efficiently collecting those datasets will be a challenging task, given the harsh environment of 200 proton-proton interactions per LHC bunch crossing. For this purpose, CMS is designing an efficient data-processing hardware trigger (Level-1) that will include tracking information and high-granularity calorimeter information. Trigger data analysis will be performed through sophisticated algorithms such as particle flow reconstruction, including widespread use of Machine Learning. The current conceptual system design is expected to take full advantage of advances in FPGA and link technologies over the coming years, providing a high-performance, lowlatency computing platform for large throughput and sophisticated data correlation across diverse sources.

The CMS HGCAL trigger data receiver

As part of the CMS Phase-2 upgrade, a prototype receiver for the HGCAL endcap front end has been implemented using the Serenity ATCA platform. The receiver firmware was developed to test the unpacking of data from the front-end endcap trigger concentrator ASIC (ECON-T) and measure its performance and stability. The firmware was integrated with prototype DAQ firmware as well as ancillary blocks to generate a trigger using ECON-T data, process scintillator trigger and timing distribution system, to evaluate the complete HGCAL vertical slice. The data was read out using custom 10G UDP links and upgraded to CMS DTH system at 25 Gbps. The system successfully achieved prototype TPG Stage-1 and DAQ path readout using generated beam triggers and delivered ~20 TB of data containing physics events at an average trigger rate of about 100 kHz.

Firmware implementation of a displaced muon reconstruction algorithm for the Phase-2 Upgrade of the CMS muon system

Displaced muons serve as a crucial indicator of novel physics extending beyond the standard model. Several theoretical frameworks posit the existence of muons with extended lifetimes, which can materialize through collisions at the LHC. This study presents the firmware implementation of an algorithm to reconstruct displaced muons using the Overlap Muon Track Finder (OMTF) of the CMS Level-1 Trigger System (L1T) targeting the High Luminosity Large Hadron Collider (HL-LHC). The firmware response is evaluated at the simulation level, comparing the results with those of the emulator, and then the algorithm is implemented on an FPGA.

Evaluation of planar silicon pixel sensors with the RD53A readout chip for the Phase-2 Upgrade of the CMS Inner Tracker

The Large Hadron Collider at CERN will undergo an upgrade in order to increase its luminosity to 7.5 × 1034 cm-2s-1. The increased luminosity during this High-Luminosity running phase, starting around 2029, means a higher rate of proton-proton interactions, hence a larger ionizing dose and particle fluence for the detectors. The current tracking system of the CMS experiment will be fully replaced in order to cope with the new operating conditions. Prototype planar pixel sensors for the CMS Inner Tracker with square 50 μm × 50 μm and rectangular 100 μm × 25 μm pixels read out by the RD53A chip were characterized in the lab and at the DESY-II testbeam facility in order to identify designs that meet the requirements of CMS during the High-Luminosity running phase. A spatial resolution of approximately 3.4 μm (2 μm) is obtained using the modules with 50 μm × 50 μm (100 μm × 25 μm) pixels at the optimal angle of incidence before irradiation. After irradiation to a 1 MeV neutron equivalent fluence of Φeq = 5.3 × 1015 cm-2, a resolution of 9.4 μm is achieved at a bias voltage of 800 V using a module with 50 μm × 50 μm pixel size. All modules retain a hit efficiency in excess of 99% after irradiation to fluences up to 2.1 × 1016 cm-2. Further studies of the electrical properties of the modules, especially crosstalk, are also presented in this paper.

Production and validation of industrially produced large-sized GEM foils for the Phase-2 upgrade of the CMS muon spectrometer

The upgrade of the CMS detector for the high luminosity LHC (HL-LHC) will include gas electron multiplier (GEM) detectors in the end-cap muon spectrometer. Due to the limited supply of large area GEM detectors, the Korean CMS (KCMS) collaboration had formed a consortium with Mecaro Co., Ltd. to serve as a supplier of GEM foils with area of approximately 0.6m2. The consortium has developed a double-mask etching technique for production of these large-sized GEM foils. This article describes the production, quality control, and quality assessment (QA/QC) procedures and the mass production status for the GEM foils. Validation procedures indicate that the structure of the Korean foils are in the designed range. Detectors employing the Korean foils satisfy the requirements of the HL-LHC in terms of the effective gain, response uniformity, rate capability, discharge probability, and hardness against discharges. No aging phenomena were observed with a charge collection of 82mCcm−2. Mass production of KCMS GEM foils is currently in progress.

The industrial production of Micro Pattern Gaseous Detector: experience from the ATLAS Micromegas

Resistive Micromegas is one of the detector technologies chosen by ATLAS for the Phase-1 upgrade of the Muon Spectrometer, completed in 2022 in view of the LHC Run3 start.It is the largest MPGD-based detector system ever built, covering an active area of 1280 m2, providing trigger and precise tracking capabilities to the ATLAS Muon system and able to stand a radiation background rate up to 20 kHz/cm2.The heart of the ATLAS Micromegas detectors is the anode board, which carries the resistive protection layer, the readout electrodes and the insulating spacers supporting the micro-mesh.The production of the 2048 readout boards of size up to 0.5×2.2 m2 has been assigned to high-technology PCB industries and required dedicated efforts for technology transfer, production follow-up and quality assurance and control.The paper reviews the main challenges from the design phase to the completion of the project which spanned over several years. Emphasis is also put on the thorough quality assurance and quality control protocol established, the achieved results, as well as on the logistic, supply and schedule constraints.The lessons learned from this unprecedented MPGD project are also discussed.

GEM detectors for the CMS endcap muon system: status of three new detector stations

The High-Luminosity LHC (HL-LHC, or Phase-2 LHC) will deliver proton-proton collisions at 5–7.5 times the nominal LHC luminosity, with an expected number of 140–200 pp-interactions per bunch crossing (Pile-up or PU). To maintain the performance of muon triggering and reconstruction under high background, the forward part of the Muon Spectrometer of the CMS experiment will be upgraded with Gas Electron Multipliers (GEM) and improved Resistive Plate Chambers (iRPC) detectors [1,2]. A first GEM station (GE1/1) was installed during Long Shutdown 2 (LS2, 2019–2021), a 2nd station (GE2/1) of Triple-GEM detectors will be installed in winter 2023–24 and 2024–25, while a new 6-layer station (ME0) will be installed in the third Long Shutdown (LS3, 2026–2028). GE11 is considered an early Phase-2 upgrade as it will reduce the pT threshold by combining GEM and Cathode Strip Chamber (CSC) hits in the forward muon system at twice the LHC design luminosity (ℒ = 2 · 1034 cm-2 s-1, 50 PU). After a successful start of Run-3 in 2022, with almost 40 fb-1 collected, the commissioning of the GE1/1 detector is nearly complete. Most chambers are operated stably with an efficiency in excess of 95%, next being the demonstration of the combined CSC-GEM trigger in 2023. The lessons learnt with the first large-area GEM station have lead to improvements in detector and electronics design for the Phase 2 detectors GE2/1 and ME0. This proceeding will discuss the progress made since last MPGD Conference (MPGD 2019) [3], discussing the commissioning and early performance of GE1/1; the design improvements and start of construction of GE2/1; and the R&D currently ongoing for ME0.

Ready for LHC Run III: the ATLAS New Small Wheel and the MicroMegas chambers performances

The two New Small Wheels (NSW) for the upgrade of the ATLAS Muon Spectrometer are now installed in the experiment and ready to collect data in LHC Run III, started in July 2022. The NSW is the largest Phase-1 upgrade project of ATLAS. Its challenging completion and readiness for data taking is a remarkable achievement of the Collaboration. The two wheels (10 meters in diameter) replace the first muon stations in the high-rapidity regions of ATLAS and are equipped with multiple layers of two new detector technologies: the small strips Thin Gap Chambers (sTGC) and the MicroMegas (MM). The latter, belong to the family of Micro Pattern Gaseous Detectors (MPGD), for the first time used in such a large scale in HEP experiments. Each detector technology will cover more than 1200 m2 of active area. The new system is designed to assure high tracking efficiency, reduction of fake trigger rates and precision measurement of muon tracks, also in view of the higher background environment foreseen for Hi-Lumi LHC. In this presentation, the motivation of the NSW upgrade and the steps from the commissioning to the data taking together with the first results using the Run III data will be presented, focusing on the MicroMegasperformances.