Francesco Fallavollita

The series of upgrades to the Large Hadron Collider, culminating in the High Luminosity Large Hadron Collider, will enable a significant expansion of the physics program of the CMS experiment. However, the accelerator upgrades will also make the experimental conditions more challenging, with implications for detector operations, triggering, and data analysis. The luminosity of the proton-proton collisions is expected to exceed $2-3\times10^{34}$~cm$^{-2}$s$^{-1}$ for Run 3 (starting in 2022), and it will be at least $5\times10^{34}$~cm$^{-2}$s$^{-1}$ when the High Luminosity Large Hadron Collider is completed for Run 4. These conditions will affect muon triggering, identification, and measurement, which are critical capabilities of the experiment. To address these challenges, additional muon detectors are being installed in the CMS endcaps, based on Gas Electron Multiplier technology. For this purpose, 161 large triple-Gas Electron Multiplier detectors have been constructed and tested. Installation of these devices began in 2019 with the GE1/1 station and will be followed by two additional stations, GE2/1 and ME0, to be installed in 2023 and 2026, respectively. The assembly and quality control of the GE1/1 detectors were distributed across several production sites around the world. We motivate and discuss the quality control procedures that were developed to standardize the performance of the detectors, and we present the final results of the production. Out of 161 detectors produced, 156 detectors passed all tests, and 144 detectors are now installed in the CMS experiment. The various visual inspections, gas tightness tests, intrinsic noise rate characterizations, and effective gas gain and response uniformity tests allowed the project to achieve this high success rate.

Triple-GEM detector technology was recently selected by CMS for a part of the upgrade of its forward muon detector system as GEM detectors provide a stable operation in the high radiation environment expected during the future High-Luminosity phase of the Large Hadron Collider (HL-LHC). In a first step, GEM chambers (detectors) will be installed in the innermost muon endcap station in the $1.6<\left|\eta\right|<2.2$ pseudo-rapidity region, mainly to control level-1 muon trigger rates after the second LHC Long Shutdown. These new chambers will add redundancy to the muon system in the $\eta$-region where the background rates are high, and the bending of the muon trajectories due to the CMS magnetic field is small. A novel construction technique for such chambers has been developed in such a way where foils are mounted onto a single stack and then uniformly stretched mechanically, avoiding the use of spacers and glue inside the active gas volume. We describe the layout, the stretching mechanism and the overall assembly technique of such GEM chambers.

Abstract In triple-GEM detectors, the segmentation of GEM foils in electrically independent sectors allows reducing the probability of discharge damage to the detector and improving the detector rate capability. However, a segmented foil presents thin dead regions in the separation between two sectors and the segmentation pattern has to be manually aligned with the GEM hole pattern during the foil manufacturing, a procedure potentially sensitive to errors. We describe the production and characterization of triple-GEM detectors obtained with an innovative GEM foil segmentation technique, the “random hole segmentation”, that allows easier manufacturing of segmented GEM foils. The electrical stability to high voltage and the gain uniformity of a random-hole segmented triple-GEM prototype are measured. The results of a test beam on a prototype assembled for the Phase-2 GEM upgrade of the CMS experiment are also presented. A high statistics efficiency measurement shows that the random hole segmentation can limit the efficiency loss of the detector in the areas between two sectors, making it a viable alternative to blank segmentation for the GEM foil manufacturing of large-area detector systems.

Abstract The documentation of the working steps, the decisions made in a reconstruction, the applied method, and the results form one of the cornerstones of scientific practice. Over the centuries, scientific publication established itself with fixed basic principles, such as verifiability of methods, objectivity, disclosure of sources, comprehensibility of argumentation, accessibility of results, accuracy, reliability, and uniformity [1]. In computer-aided, hypothetical 3D reconstruction of destroyed architecture, the application of the above basic principles faces an as yet unsolved challenge. The model creation process is rarely documented, and when it is, the documentation is usually not publicly available. The knowledge embedded in reconstructions, scientific interpretation, argumentation, and hypothesis, is in danger of being lost. Due to the lack of resources, diverse and rapidly developing software applications, modelling methods and types, no application-based method for documenting and publishing 3D models has been established. Three decades into the spread of computer-assisted 3D visualization in the research and mediation of cultural heritage, discussion of the question of what and how to document has intensified. The Internet as a publication venue seems to make sense to most. Web-based documentation requires technical infrastructures and services as well as defined scientific methods for comprehensible modeling and sustainable provision. The following chapter is dedicated to describing and clarifying these developments.

Abstract. The sixteenth-century Fountain of Neptune is one of Bologna’s most renowned landmarks. During the recent restoration activities of the monumental sculpture group, consisting in precious marbles and highly refined bronzes with water jets, a photographic campaign has been carried out exclusively for documentation purposes of the current state of preservation of the complex. Nevertheless, the highquality imagery was used for a different use, namely to create a 3D digital model accurate in shape and color by means of automated photogrammetric techniques and a robust customized pipeline. This 3D model was used as basic tool to support many and different activities of the restoration site. The paper describes the 3D model construction technique used and the most important applications in which it was used as support tool for restoration: (i) reliable documentation of the actual state; (ii) surface cleaning analysis; (iii) new water system and jets; (iv) new lighting design simulation; (v) support for preliminary analysis and projectual studies related to hardly accessible areas; (vi) structural analysis; (vii) base for filling gaps or missing elements through 3D printing; (viii) high-quality visualization and rendering and (ix) support for data modelling and semantic-based diagrams.

The high-luminosity phase of the Large Hadron Collider (HL-LHC) will result in ten times higher particle background than measured during the first phase of LHC operation. In order to fully exploit the highly-demanding operating conditions during HL-LHC, the Compact Muon Solenoid (CMS) Collaboration will use Gas Electron Multiplier (GEM) detector technology. The technology will be integrated into the innermost region of the forward muon spectrometer of CMS as an additional muon station called GE1∕1. The primary purpose of this auxiliary station is to help in muon reconstruction and to control level-1 muon trigger rates in the pseudo-rapidity region 1.6≤|η|≤2.2. The new station will contain trapezoidal-shaped GEM detectors called GE1∕1 chambers. The design of these chambers is finalized, and the installation is in progress during the Long Shutdown phase two (LS-2) that started in 2019. Several full-size prototypes were built and operated successfully in various test beams at CERN. We describe performance measurements such as gain, efficiency, and time resolution of these prototype chambers, developed after years of R&D, and summarize their behavior in different gas compositions as a function of the applied voltage.

Abstract The high-luminosity LHC (HL-LHC) upgrade is presenting new challenges for particle detector technologies. In the CMS muon system gaseous detectors, the increase in luminosity will produce a particle background ten times higher than at the LHC. To cope with the high rate environment and maintain current performance, the triple-gas electron multiplier technology is a promising candidate for high-rate capable detectors for the CMS-ME0 upgrade project in the innermost region of the forward muon spectrometer of the CMS experiment. An intense R&amp;D and prototyping phase is currently ongoing to prove that such technology meets the stringent performance requirements of highly efficient particle detection in the harsh background environment expected in the innermost ME0 region. Here, we describe the recent rate capability studies of triple-GEM detectors operated with an Ar/CO 2 (70/30) gas mixture at an effective gas gain of 2 × 10 4 by using a high intensity 22 keV X-ray generator. Moreover, we present a novel foil design based on double-sided segmented GEM-foils, high voltage power distribution and filtering, which the CMS muon collaboration adopted for realization of the CMS-ME0 project, and their impact on the performance of the detector in the light of new rate capability studies, with a summary of the ongoing R&amp;D activities.

This contribution introduces a new type of Micropattern Gaseous Detector, the Fast Timing Micropattern (FTM) detector, utilizing fully Resistive WELL structures. The structure of the prototype will be described in detail and the results of the characterization study performed with an X-ray gun will be presented, together with the first results on time resolution based on data collected with muon/pion test beams.

In the framework of the High-Luminosity Large Hadron Collider project (HL-LHC), the LHC experiments will require upgrades to their detectors to cope with the new accelerator performance. The upgrade of the CMS Muon Spectrometer foresees the installation of three new muon stations based on the Gas Electron Multiplier (GEM) technology, referred to as GE1/1, GE2/1 and ME0 detectors. While the installation and commissioning of the GE1/1 detectors is currently underway, the GE2/1 and ME0 detectors are expected to be installed between 2023 and 2027. The CMS Muon Collaboration has developed a novel construction design of large-area, trapezoidal-shaped GE1/1 triple-GEM detectors; in particular, a new self-stretching technique has been introduced to mechanically stretch the GEM-foils without using spacer grids or glue inside the gas volume in order to avoid dead regions (several percent) or possibly outgassing contaminants which could trigger premature aging processes. As it has been observed, the PCB boards, which define the gas enclosure of the detector, get deformed under the internal gas over-pressure, introducing irregularities in the planarity of the GE1/1 detector, which could potentially affect the uniformity of the detector performance. Therefore, the collaboration has established a set of tests and quality controls in order to quantify these irregularities and mitigate their impact on detector performance. Additionally, new solutions and design upgrades have been implemented to prevent such effects in future GE2/1 and ME0 upgrade projects. We will focus in particular on the novel design solutions based on the PCB distance holders (pillars), which the collaboration adopted for realization of the latter projects, and their impact on the performance of the detector, with a summary of the ongoing R&D activities.

Abstract. Fortresses and castles are important symbols of social and cultural identity providing tangible evidence of cultural unity in Europe. They are items for which it is always difficult to outline a credible prospect of reuse, their old raison d'être- namely the military, political and economic purposes for which they were built- having been lost. In recent years a Research Unit of the University of Bologna composed of architects from different disciplines has conducted a series of studies on fortified heritage in the Emilia Romagna region (and not only) often characterized by buildings in ruins. The purpose of this study is mainly to document a legacy, which has already been studied in depth by historians, and previously lacked reliable architectural surveys for the definition of a credible as well as sustainable conservation project. Our contribution will focus on different techniques and methods used for the survey of these architectures, the characteristics of which- in the past- have made an effective survey of these buildings difficult, if not impossible. The survey of a ruin requires, much more than the evaluation of an intact building, reading skills and an interpretation of architectural spaces to better manage the stages of documentation and data processing. Through a series of case studies of fortified buildings in ruins, we intend to describe the reasons that guided the choice of the methods and tools used and to highlight the potentials and the limits of these choices in financial terms.

Gas Electron Multiplier (GEM) technology, in particular triple-GEM, was selected for the upgrade of the CMS endcap muon system following several years of intense effort on R&D. The triple-GEM chambers (GE1/1) are being installed at station 1 during the second long shutdown with the goal of reducing the Level-1 muon trigger rate and improving the tracking performance in the harsh radiation environment foreseen in the future LHC operation [1]. A first installation of a demonstrator system started at the beginning of 2017: 10 triple-GEM detectors were installed in the CMS muon system with the aim of gaining operational experience and demonstrating the integration of the GE1/1 system into the trigger. In this context, a dedicated Detector Control System (DCS) has been developed, to control and monitor the detectors installed and integrating them into the CMS operation. This paper presents the slice test DCS, describing in detail the different parts of the system and their implementation.

The CMS muon system in the region with 2.03<|η|<2.82 is characterized by a very harsh radiation environment which can generate hit rates up to 144 kHz/cm2 and an integrated charge of 8 C/cm2 over ten years of operation. In order to increase the detector performance and acceptance for physics events including muons, a new muon station (ME0) has been proposed for installation in that region. The technology proposed is Triple—Gas Electron Multiplier (Triple-GEM), which has already been qualified for the operation in the CMS muon system. However, an additional set of studies focused on the discharge probability is necessary for the ME0 station, because of the large radiation environment mentioned above. A test was carried out in 2017 at the Cern High energy AcceleRator Mixed (CHARM) facility, with the aim of giving an estimation of the discharge probability of Triple-GEM detectors in a very intense radiation field environment, similar to the one of the CMS muon system. A dedicated standalone Geant4 simulation was performed simultaneously, to evaluate the behavior expected in the detector exposed to the CHARM field. The geometry of the detector has been carefully reproduced, as well as the background field present in the facility. This paper presents the results obtained from the Geant4 simulation, in terms of sensitivity of the detector to the CHARM environment, together with the analysis of the energy deposited in the gaps and of the processes developed inside the detector. The discharge probability test performed at CHARM will be presented, with a complete discussion of the results obtained, which turn out to be consistent with measurements performed by other groups.

The CMS Collaboration has been developing large-area triple-gas electron multiplier (GEM) detectors to be installed in the muon Endcap regions of the CMS experiment in 2019 to maintain forward muon trigger and tracking performance at the High-Luminosity upgrade of the Large Hadron Collider (LHC); 10 preproduction detectors were built at CERN to commission the first assembly line and the quality controls (QCs). These were installed in the CMS detector in early 2017 and participated in the 2017 LHC run. The collaboration has prepared several additional assembly and QC lines for distributed mass production of 160 GEM detectors at various sites worldwide. In 2017, these additional production sites have optimized construction techniques and QC procedures and validated them against common specifications by constructing additional preproduction detectors. Using the specific experience from one production site as an example, we discuss how the QCs make use of independent hardware and trained personnel to ensure fast and reliable production. Preliminary results on the construction status of CMS GEM detectors are presented with details of the assembly sites involvement.

To extend the acceptance of the CMS muon spectrometer to the region 2.4< |η| <2.8, stacks of triple-GEM chambers, forming the ME0 station, are planned for the CMS Phase 2 Upgrade. These large-area micro-pattern gaseous detectors must operate in a challenging environment with expected background particle fluxes up to 150 kHz/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Unlike traditional non-resistive gaseous detectors, the rate capability of such triple-GEM detectors is limited not by space charge effects, but by voltage drops on the chamber electrodes due to avalanche-induced currents flowing through the resistive protection circuits (introduced as discharge quenchers). We present a study of the irradiation of large-area triple-GEM detectors with moderate fluxes to obtain a high integrated hit rate. The results show drops as high as 40% of the nominal detector gas gain, which would result in severe loss of tracking efficiency. We discuss possible mitigation strategies leading to a new design for the GEM foils with electrode segmentation in the radial direction, instead of the 'traditional" transverse segmentation. The advantages of the new design include uniform hit rate across different sectors, minimization of gain-loss without the need for voltage compensation, and independence of detector gain on background flux shape.

Cosmic ray radiation is mostly composed, at sea level, by high energy muons, which are highly penetrating particles capable of crossing kilometers of rock. Cosmic ray radiation constituted the first source of projectiles used to investigate the intimate structure of matter and is currently and largely used for particle detector test and calibration. The ubiquitous and steady presence at the Earth's surface and the high penetration capability has motivated the use of cosmic ray radiation also in fields beyond particle physics, from geological and archaeological studies to industrial applications and civil security. In the present paper, cosmic ray muon detection techniques are assessed for stability monitoring applications in the field of civil engineering, in particular for static monitoring of historical buildings, where conservation constraints are more severe and the time evolution of the deformation phenomena under study may be of the order of months or years. As a significant case study, the monitoring of the wooden vaulted roof of the "Palazzo della Loggia" in the town of Brescia, in Italy, has been considered. The feasibility as well as the performances and limitations of a monitoring system based on cosmic ray tracking, in the considered case, have been studied by Monte Carlo simulation and discussed in comparison with more traditional monitoring systems. Requirements for muon detectors suitable for this particular application, as well as the results of some preliminary tests on a muon detector prototype based on scintillating fibers and silicon photomultipliers SiPM are presented.

In triple-GEM detectors, the segmentation of GEM foils in electrically independent sectors allows reducing the probability of discharge damage to the detector and improving the detector rate capability; however, a segmented foil presents thin dead regions in the separation between two sectors and the segmentation pattern has to be manually aligned with the GEM hole pattern during the foil manufacturing, a procedure potentially sensitive to errors. We describe the production and characterization of triple-GEM detectors produced with an innovative GEM foil segmentation technique, the ``random hole segmentation'', that allows an easier manufacturing of segmented GEM foils. The electrical stability to high voltage and the gain uniformity of a random-hole segmented triple-GEM prototype are measured. The results of a test beam on a prototype assembled for the Phase-2 GEM upgrade of the CMS experiment are also presented; a high-statistics efficiency measurement shows that the random hole segmentation can limit the efficiency loss of the detector in the areas between two sectors, making it a viable alternative to blank segmentation for the GEM foil manufacturing of large-area detector systems.

The CMS experiment is a general-purpose detector installed in the Large Hadron Collider (LHC) at CERN. During the High Luminosity LHC phase, the luminosity is expected to increase by a factor of 10 compared to the LHC design value. The forward region of the CMS muon system will be equipped with 3 additional triple GEM-based muon stations, where GEM stands for Gas Electron Multiplier. The three stations, in order of distance from the interaction point, are called ME0, GE1/1, and GE2/1. The ME0 station, where ME stands for Muon Endcap, is located just behind the new endcap calorimeter, where the background particle flux can reach up to 150 kHz/cm$^{2}$. Recent studies of rate capability and gain drop resulted in a design change in the segmentation of the high voltage (HV) distribution for the GEM foils. The second-generation ME0 prototype has radial segments in contrast to the (approximate) segmentation in pseudorapidity employed for GE1/1 and GE2/1. In this report, we describe the mechanical design of the second-generation prototype, the simulation of the background counting rate in the HV segments, and the measurement of the energy spectrum, the effective gain, and the response uniformity.

To accommodate the anticipated increase in luminosity, the ATLAS experiment at CERN is currently undergoing upgrades. The instantaneous luminosity, in the coming years, is anticipated to attain 7.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . The most complex upgrade project involves the replacement of the Muon Spectrometer’s inner end-cap detection stations, known as New Small Wheels (NSWs). The NSWs employ novel micro-pattern gaseous detector technology, which aims to improve system performance both in terms of trigger accuracy and spatial resolution. In order to evaluate the operational characteristics of the Micromegas chambers as well as of the associated readout electronics, a plethora of tests were performed at the new CERN Gamma Irradiation Facility (GIF++). This article describes the experimental setup and highlights the tests of the electronics response as a function of the gamma intensity.

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 0.6 m2. 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 82 mC cm−2. Mass production of KCMS GEM foils is currently in progress.

Abstract The Gas Electron Multiplier (GEM) detectors of the GE1/1 station of the CMS experiment have been operated in the CMS magnetic field for the first time on the 7 th of October 2021. During the magnetic field ramps, several discharge phenomena were observed, leading to instability in the GEM High Voltage (HV) power system. In order to reproduce the behavior, it was decided to conduct a dedicated test at the CERN North Area with the Goliath magnet, using four GE1/1 spare chambers. The test consisted in studying the characteristics of discharge events that occurred in different detector configurations and external conditions. Multiple magnetic field ramps were performed in sequence: patterns in the evolution of the discharge rates were observed with these data. The goal of this test is the understanding of the experimental conditions inducing discharges and short circuits in a GEM foil. The results of this test lead to the development of procedure for the optimal operation and performance of GEM detectors in the CMS experiment during the magnet ramps. Another important result is the estimation of the probability of short circuit generation, at 68 % confidence level, p short HV OFF = 0.42 -0.35 +0.94 % with detector HV OFF and p short HV OFF &lt; 0.49% with the HV ON. These numbers are specific for the detectors used during this test, but they provide a first quantitative indication on the phenomenon, and a point of comparison for future studies adopting the same procedure.

Resistive plate chambers (RPCs) with electrodes of high-pressure phenolic laminate and small gas gap widths down to 1 mm provide large area tracking at relatively low cost in combination with high rate capability and fast response with excellent time resolution of better than 500 ps. They are perfectly suited for experiments requiring sub-nanosecond time resolution and spatial resolution on the order of a few millimeters over large areas. Thin-gap RPCs will therefore be used for the upgrade of the barrel muon system of the ATLAS experiment at HL-LHC and are candidates for the instrumentation of future collider detectors and experiments searching for long-lived particles in experiments like ANUBIS. RPCs are also frequently used in large area cosmic ray detectors. The large demand for RPCs exceeds the presently available production capacities. At the same time, the requirements on mechanical precision, reliability and reproducibility for collider detectors have increased, especially with the reduced gas gap widths. Additional suppliers with industry-style quality assurance are therefore urgently needed. We have established RPC production procedures compliant with industrial requirements and are in the process of certifying several companies for RPC production for the ATLAS upgrade for HL-LHC and beyond. We report about the technology transfer, the RPC prototype production at the selected companies and the results of the certification procedure, as well as their performance and stability measurements in laboratory tests and at CERN SPS X5 120GeV muon beams under high rate <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs irradiation.

We present the results of aging and discharge probability studies of CMS (Compact Muon Solenoid) triple-GEM detectors. These studies has been performed in the framework of an R&D activity on triple-GEM detectors for the innermost region of the muon spectrometer of the CMS experiment in order to confirm the robustness of the triple-GEM technology and evaluate the effect of the irradiation and neutron-induced discharges on the long-term detector operation.

Abstract We present here a new study of the aging of Triple-GEM detectors in contaminated environment. The goal of this experiment is to evaluate the influence of the ionization power of particles on the longevity of the gaseous detectors and therefore determine the best configurations required to reliably reproduce the classical aging phenomena in laboratory. A 100 cm 2 triple-GEM detector operating in Ar/CO 2 (70/30%) was irradiated simultaneously with low energy X-rays and 5.5 MeV alpha particles. Hydrocarbons and Si-based molecules were added to the gas mixture in order to accelerate the aging and simulating many years of slow gas pollution. We measured the evolution of the detector performance in two irradiated zones and we performed a systematic chemical analysis of the GEM foils to measure the polymer concentration and thus the potential aging effects. The detector collected a total charge of 165 mC/cm 2 in the two irradiated sectors with no performance loss. Chemical analysis revealed a greater Si-based polymers concentration in the region irradiated with alpha particles. This is due to their higher ionization power, with respect to low energy X-rays, which generate denser electron avalanches and, thus, a higher polymerization rate. Further studies have to be performed in order to validate this result, at different experimental conditions and with different detector technologies.

Abstract A temperature monitoring system based on fibre Bragg grating (FBG) fibre optic sensors has been developed for the gas electron multiplier (GEM) chambers of the Compact Muon Solenoid (CMS) detector. The monitoring system was tested in prototype chambers undergoing a general test of the various technological solutions adopted for their construction. The test lasted about two years and was conducted with the chambers being installed in the CMS detector and operated during regular experimental running. In this paper, we present test results that address the choice of materials and procedures for the production and installation of the FBG temperature monitoring system in the final GEM chambers.

We present analytical calculations, Finite Element Analysis modelling, and physical measurements of the interstrip capacitances for different potential strip geometries and dimensions of the readout boards for the GE2/1 triple-Gas Electron Multiplier detector in the CMS muon system upgrade. The main goal of the study is to find configurations that minimize the interstrip capacitances and consequently maximize the signal-to-noise ratio for the detector. We find agreement at the 1.5–4.8% level between the two methods of calculations and on the average at the 17% level between calculations and measurements. A configuration with halved strip lengths and doubled strip widths results in a measured 27–29% reduction over the original configuration while leaving the total number of strips unchanged. We have now adopted this design modification for all eight module types of the GE2/1 detector and will produce the final detector with this new strip design.

To extend the acceptance of the CMS muon spectrometer to the region 2.4 $<|\eta|<$ 2.8, stacks of triple-GEM chambers, forming the ME0 station, are planned for the CMS Phase 2 Upgrade. These large-area micro-pattern gaseous detectors must operate in a challenging environment with expected background particle fluxes up to 150 kHz/cm$^2$. Unlike traditional non-resistive gaseous detectors, the rate capability of such triple-GEM detectors is limited not by space charge effects, but by voltage drops on the chamber electrodes due to avalanche-induced currents flowing through the resistive protection circuits (introduced as discharge quenchers). We present a study of the irradiation of large-area triple-GEM detectors with moderate fluxes to obtain a high integrated hit rate. The results show drops as high as 40% of the nominal detector gas gain, which would result in severe loss of tracking efficiency. We discuss possible mitigation strategies leading to a new design for the GEM foils with electrode segmentation in the radial direction, instead of the "traditional" transverse segmentation. The advantages of the new design include uniform hit rate across different sectors, minimization of gain-loss without the need for voltage compensation, and independence of detector gain on background flux shape.

The high-luminosity LHC (HL-LHC) upgrade is presenting new challenges for particle detector technologies. In the CMS Muon System gaseous detectors, the increase in luminosity will produce a particle background ten times higher than at the LHC. To cope with the high rate environment and maintain current performance, the triple-Gas Electron Multiplier technology is a promising candidate for high-rate capable detectors for the CMS-ME0 upgrade project in the innermost region of the forward Muon Spectrometer of the CMS experiment. An intense R&amp;D and prototyping phase is currently ongoing to prove that such technology meets the stringent performance requirements of highly efficient particle detection in the harsh background environment expected in the innermost ME0 region. Here we describe the recent rate capability studies of triple-GEM detectors operated with an Ar/CO 2 (70/30) gas mixture at an effective gas gain of 2 × 10 4 by using a high intensity 22 keV X-ray generator. Moreover, we present a novel foils design based on double-sided segmented GEM-foils, high voltage power distribution, and filtering, which the collaboration adopted for realization of the latter projects, and their impact on the performance of the detector in the light of new rate capability studies, with a summary of the ongoing R&amp;D activities.

The high-luminosity LHC (HL-LHC) upgrade is setting a new challenge for particle detection technologies. In the CMS muon system based on gas detectors,the increased luminosity will yield a ten times higher particle background compared to the present LHC conditions. To cope with the high-rate environment and to maintain the actual performance, new Gas Electron Multiplier (GEM)detector swill be installed in the innermost region of the forward CMS muon spectrometer, 2 <η < 2.8 (ME0 project). The detailed knowledge of the detector performance in the presence of such a high background is crucial for an optimized design and efficient operation at the HLLHC. A precise understanding of possible aging effects of detector materials and gases is of extreme importance. For this reason, aging tests of full sized triple-GEM detector operated with an Ar/CO2 (70/30) gas mixture at an effective gas gain of 2×10^4, are in course at GIF++, the CERN Gamma Irradiation Facility. One detector is irradiated with 662 keV gamma - rays from a 14 TBq 137Cs source and, in parallel, a second similar detector with 22 keV X-rays at the quality control lab. This contribution describes the performance of triple-GEM detectors during the irradiation test and reports on their state-of-the art.

Abstract The foreseen upgrade of the Large Hadron Collider (LHC) will lead to an increase of its luminosity up to 5 – 7 × 10 34 cm −2 s −1 , five times more than the original design value. The CMS muon system must be able to sustain a physics program after the increase of luminosity and maintain sensitivity for electroweak physics for TeV scale searches achieved during Run2. To cope with the corresponding increase in background rates and trigger requirements, the installation of additional sets of muon detectors based on Gas Electron Multiplier (GEM) technology, referred to as GE1/1, GE2/1 and ME0, has been planned. The installation and commissioning of the GE1/1 detectors in the CMS experiment have been scheduled in two separate phases: the first 72 detectors have been already installed together with their services (gas, cooling, low voltage and high voltage) in 2019 and they are undergoing the commissioning phase, while the completion of the station is foreseen in autumn 2020. The author will describe the detector design, the quality assurance and certification path, as well as will present the status of the installation and commissioning, worth its preliminary results and an overview for the complete integration of the GE1/1 project on the CMS experiment.

The Phase-II high luminosity upgrade to the Large Hadron Collider (LHC) is planned for 2023, significantly increasing the collision rate and therefore the background rate, particularly in the high $\eta$ region. To improve both the tracking and triggering of muons, the Compact Muon Solenoid (CMS) Collaboration plans to install triple-layer Gas Electron Multiplier (GEM) detectors in the CMS muon endcaps. Demonstrator GEM detectors were installed in CMS during 2017 to gain operational experience and perform a preliminary investigation of detector performance. We present the results of triple-GEM detector performance studies performed in situ during normal CMS and LHC operations in 2018. The distribution of cluster size and the efficiency to reconstruct high $p_T$ muons in proton--proton collisions are presented as well as the measurement of the environmental background rate to produce hits in the GEM detector.

Abstract In 2018, a system of large-size triple-GEM demonstrator chambers was installed in the CMS experiment at CERN's Large Hadron Collider (LHC). The demonstrator's design mimicks that of the final detector, installed for Run-3. A successful Monte Carlo (MC) simulation of the collision-induced background hit rate in this system in proton-proton collisions at 13 TeV is presented. The MC predictions are compared to CMS measurements recorded at an instantaneous luminosity of 1.5 ×10 34 cm -2 s -1 . The simulation framework uses a combination of the FLUKA and GEANT4 packages. FLUKA simulates the radiation environment around the GE1/1 chambers. The particle flux by FLUKA covers energy spectra ranging from 10 -11 to 10 4 MeV for neutrons, 10 -3 to 10 4 MeV for γ's, 10 -2 to 10 4 MeV for e ± , and 10 -1 to 10 4 MeV for charged hadrons. GEANT4 provides an estimate of the detector response (sensitivity) based on an accurate description of the detector geometry, the material composition, and the interaction of particles with the detector layers. The detector hit rate, as obtained from the simulation using FLUKA and GEANT4, is estimated as a function of the perpendicular distance from the beam line and agrees with data within the assigned uncertainties in the range 13.7-14.5%. This simulation framework can be used to obtain a reliable estimate of the background rates expected at the High Luminosity LHC.