Muon System Research Articles

Upgrade of the CMS muon system

This contribution illustrates the four different detector technologies used in the muon spectrometer of the Compact Muon Solenoid (CMS) experiment, installed on the Large Hadron Collider (LHC), and their future upgrades. These have the aim to cope with the scheduled increase of instantaneous luminosity of the LHC in the so-called High-Luminosity LHC phase. CMS Collab. [J. Instrum. 3, S08004 (2008), doi:10.1088/1748-0221/3/08/S08004].

ATLAS upgrade for the HL-LHC

While the on-going Run-3 data-taking campaign will provide twice the integrated proton–proton luminosity currently available at the LHC, most of the data expected for the full LHC physics program will only be delivered during the HL-LHC phase. For this, the LHC will undergo an ambitious upgrade program to be able to deliver an instantaneous luminosity of 7.5⋅1034cm−2s−1, allowing the collection of more than 3 ab−1 of data at s=13.6(14)TeV. This unprecedented data sample will allow the ATLAS experiment to perform several precision measurements to constrain the Standard Model (SM) in yet unexplored regions of phase space, in particular in the Higgs sector, only accessible at the LHC. To benefit from such a rich data sample, it is fundamental to upgrade the detector to cope with the challenging experimental conditions that include radiation doses 10 times higher than what ATLAS experienced since its construction and increase in the number of interactions per bunch crossing from the current 50-60 to 200. The upgrade of the ATLAS detector comprises a completely new all-silicon tracker with extended rapidity coverage that will replace the current inner tracker detector; a redesigned trigger and data acquisition system for the calorimeters and muon systems, allowing the implementation of a readout system that can operate complex trigger algorithms at 40 MHz. Finally, a new subsystem called High Granularity Timing Detector will aid the track-vertex association in the forward region by providing timing information to the reconstructed tracks. An important ingredient, relevant to almost all measurements, is the precise determination of the delivered luminosity with systematic uncertainties below the percent level. This challenging task will be achieved by collecting the information from several detector systems using different and complementary techniques. This document will describe the ongoing ATLAS detector upgrade status and the main results obtained with the prototypes, giving a synthetic view of the whole upgrade project.

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The CMS detector, including its muon system, has been operating at the CERN LHC in increasingly challenging conditions for about 15 years. The muon detector was designed to provide excellent triggering and track reconstruction for muons produced in proton–proton collisons at an instantaneous luminosity (L\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {L}$$\\end{document}) of 1×1034\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1 \ imes 10^{34}$$\\end{document} cm-2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-2}$$\\end{document}s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document}. During the Run 2 data-taking period (2015–2018), the LHC achieved an instantaneous luminosity of twice its design value, resulting in larger background rates and making the efficient detection of muons more difficult. While some backgrounds result from natural radioactivity, cosmic rays, and interactions of the circulating protons with residual gas in the beam pipe, the dominant source of background hits in the muon system arises from proton–proton interactions themselves. Charged hadrons leaving the calorimeters produce energy deposits in the muon chambers. In addition, high-energy particles interacting in the hadron calorimeter and forward shielding elements generate thermal neutrons, which leak out of the calorimeter and shielding structures, filling the CMS cavern. We describe the method used to measure the background rates in the various muon subsystems. These rates, in conjunction with simulations, can be used to estimate the expected backgrounds in the High-Luminosity LHC. This machine will run for at least 10 years starting in 2029 reaching an instantaneous luminosity of L=5×1034cm-2s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {L} = 5 \ imes \ ext {10}^\ ext {34}\\,\ ext {cm}^\ ext {-2}\\,\ ext {s}^\ ext {-1}$$\\end{document} and increasing ultimately to L=7.5×1034cm-2s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {L} = 7.5 \ imes \ ext {10}^\ ext {34}\\,\ ext {cm}^\ ext {-2}\\,\ ext {s}^\ ext {-1}$$\\end{document}. These background estimates have been a key ingredient for the planning and design of the muon detector upgrade.

Search for long-lived heavy neutral leptons decaying in the CMS muon detectors in proton-proton collisions at s=13 TeV

A search for heavy neutral leptons (HNLs) decaying in the CMS muon system is presented. A data sample is used corresponding to an integrated luminosity of 138 fb−1 of proton-proton collisions at s=13 TeV, recorded at the CERN LHC in 2016–2018. Decay products of long-lived HNLs could interact with the shielding materials in the CMS muon system and create hadronic and electromagnetic showers detected in the muon chambers. This distinctive signature provides a unique handle to search for HNLs with masses below 4 GeV and proper decay lengths of the order of meters. The signature is sensitive to HNL couplings to all three generations of leptons. Candidate events are required to contain a prompt electron or muon originating from a vertex on the beam axis and a displaced shower in the muon chambers. No significant deviations from the standard model background expectation are observed. In the electron (muon) channel, the most stringent limits to date are set for HNLs in the mass range of 2.1–3.0 (1.9–3.3) GeV, reaching mixing matrix element squared values as low as 8.6(4.6)×10−6. © 2024 CERN, for the CMS Collaboration 2024 CERN

Irradiation effects on GEM detectors operated at RUN1 and RUN2 at the LHCb experiment

Triple-GEM detectors with pad readout have been employed to equip the innermost region (R1) of the first station (M1) within the Muon system of the LHCb experiment. The GEM detectors have been operated with an Ar/CO2/CF4 = 45/15/40 gas mixture at a gas gain of about 4000 with an average particle flux of about 250 kHz/cm2. Throughout RUN1 and RUN2, spanning approximately 440 days of colliding beams, the GEM detectors accumulated a charge of up to 0.5 C/cm2. This paper presents a comparative analysis between a global irradiation test of GEM detectors at the Calliope facility (ENEA-Casaccia, 1.25 MeV γ ray flux from a 60Co source) and the GEMs operated at LHCb, focusing on the impacts of a CF4-based gas mixture. In both instances, the detectors were opened and the GEM foils were examined by the EN-MME-MM CERN group with a Field Emission Gun Scanning Electron Microscope (FEG-SEM) for a magnified image analysis and an X-Max Energy Dispersive X-ray Spectroscopy (EDS) for the chemical one.

The SHADOWS experiment at the CERN SPS

SHADOWS (Search for Hidden And Dark Objects With the SPS) is a proposed proton beam-dump experiment for the search of a large variety of Feebly-Interacting Particles (FIPs) at the CERN SPS. It will exploit the potential for searches and discoveries at the intensity frontier offered by the upgrade of the ECN3 beam line.SHADOWS will be located off-axis, which allows the optimisation of the signal-to-background ratio, and will collect data from up to 5×1019 protons of 400 GeV on target in 4 years of operations.The experiment has a transversal size of 2.5×2.5 m2 and is composed by an upstream veto, a 20 m long decay volume and a spectrometer with a tracking system in a dipole magnet, a timing detector, a calorimeter and a muon system. The conceived detector offers excellenttracking and timing performance for the identification and reconstruction of most of the visible final states of FIP decays. SHADOWS will allow to explore a large parameter space region of many FIPs, like light dark scalars, axion-like particles and heavy neutral leptons, with masses ranging between 0.1 and 10 GeV.This paper reports about the status of the proposal of the SHADOWS experiment, with focus on the detector challenges.

Automated object detection for muon tomography data analysis

In recent years, there have been ongoing efforts to improve screening technologies to improve security and prevent terrorist threats. The most widely used technologies for scanning shipping containers are gamma and X-ray radiography, which can be harmful to operators and the environment. Muon tomography screening systems are considered as a potential tool to enhance border security and prevent terrorist threats or smuggling, especially in the context of shipping container inspections. Muon tomography uses naturally occurring cosmic ray muons to create detailed images of the inside of objects, such as shipping containers, without the need for physical intervention. Various realistic smuggling scenarios were simulated using the GEANT4 toolkit. The implemented filtering algorithms successfully reduce background noise from the surrounding cargo, enabling the detection of concealed threats and contraband. With the tools provided by the ROOT data analysis package, prohibited items can be automatically detected and localized in a cargo container.

Longevity studies for the CMS Drift Tubes towards HL-LHC

The High Luminosity LHC (HL-LHC) program will pose a great challenge for the CMS Muon System. Existing subdetectors, which consist of Drift Tubes (DT), Resistive Plate Chambers (RPC) and Cathode Strip Chambers (CSC), will have to operate at 5 times larger instantaneous luminosity than the designed for, and, consequently, will have to sustain about 10 times the original LHC integrated luminosity. Longevity of DT system will be crucial to ensure a good performance in the CMS barrel region. Assessing DT performance is part of the upgrade program. In this talk will be reported the outcome of the accelerated irradiation studies, carried on at the CERN Gamma Irradiation Facility (GIF++) and recently concluded. These studies allowed to estimate performance of DT up to 3 times HL-LHC, and to plan a strategy to keep the longevity effects under control.

The LHCb Upgrade I

The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software.

Development of the CMS detector for the CERN LHC Run 3

Since the initial data taking of the CERN LHC, the CMS experiment has undergone substantial upgrades and improvements. This paper discusses the CMS detector as it is configured for the third data-taking period of the CERN LHC, Run 3, which started in 2022. The entire silicon pixel tracking detector was replaced. A new powering system for the superconducting solenoid was installed. The electronics of the hadron calorimeter was upgraded. All the muon electronic systems were upgraded, and new muon detector stations were added, including a gas electron multiplier detector. The precision proton spectrometer was upgraded. The dedicated luminosity detectors and the beam loss monitor were refurbished. Substantial improvements to the trigger, data acquisition, software, and computing systems were also implemented, including a new hybrid CPU/GPU farm for the high-level trigger.

SND@LHC: the scattering and neutrino detector at the LHC

SND@LHC is a compact and stand-alone experiment designed to perform measurements with neutrinos produced at the LHC in the pseudo-rapidity region of 7.2 < η < 8.4. The experiment is located 480 m downstream of the ATLAS interaction point, in the TI18 tunnel. The detector is composed of a hybrid system based on an 830 kg target made of tungsten plates, interleaved with emulsion and electronic trackers, also acting as an electromagnetic calorimeter, and followed by a hadronic calorimeter and a muon identification system. The detector is able to distinguish interactions of all three neutrino flavours, which allows probing the physics of heavy flavour production at the LHC in the very forward region. This region is of particular interest for future circular colliders and for very high energy astrophysical neutrino experiments. The detector is also able to search for the scattering of Feebly Interacting Particles. In its first phase, the detector is ready to operate throughout LHC Run 3 and collect a total of 250 fb-1.

Fast timing detectors for the muon system of a muon collider experiment: requirements from simulation and prototype performance

Looking at the future path of high-energy physics, a muon collider offers incomparable potential for discovery in the multi-TeV energy range. However, its development must address some relevant technological challenges, which arise from the short muon lifetime, 2.2 μs, and from the difficulty of producing large numbers of muons in groups with small emittance. The first one in particular leads to the production of the so-called Beam-induced Background (BIB), which affects the design of the machine and detector.The purpose of this contribution is to describe the expected performance of the muon system of a multipurpose muon collider detector designed to reconstruct the products of multi-TeV collisions with extreme accuracy.We are proposing a design of the muon system fully based on Micropattern Gaseous Detectors (MPGD), which foresees the combination of tracking layers based on Triple-GEM detectors, with a timing layer based on a new generation MPGD called Picosec. Picosec was developed in the last few years by the RD51 collaboration, with the aim of obtaining a fast timing (sub ns) MPGD.A dedicated R&D is ongoing to optimize such a technology for the application in a muon collider experiment, both from the detector and the mechanics point of views.This contribution will present the results obtained during the R&D of the Picosec technology for the muon collider both from laboratory tests and test beams performed in 2023. Special attention will be given to the performance obtained with different gas mixtures. Moreover, we will discuss the plans for the R&D dedicated to the muon collider.

Design validation of the CMS Phase-2 Triple-GEM detectors

The High-Luminosity LHC will deliverproton-proton collisions at 5.0–7.5 times the nominal LHC luminosity, with anexpected number of 140–200 pp-interactions per bunch crossing. To maintain the performance of muon triggering and reconstruction underhigh background, the forward part of the Muon spectrometer of the CMSexperiment will be upgraded with Gas Electron Multipliers (GEM) and improvedResistive Plate Chambers detectors. Particularly challenging isthe extension of the pseudorapidity of the muon system up to |η| < 2.8with a 6-layer station, named ME0, that will be installed behind the newhigh granularity calorimeter and that will see particle rates up to150 kHz/cm2 and integrate a dose of 250 krad by the end of the High Luminosity phase of the LHC.In this contribution we will present the major design changes of the Triple-GEMdetectors to adapt them for the harsh radiation environment and the highparticle rate. We shall summarize the performance of prototype Triple-GEMdetectors measured with X-rays and gamma at theCERN GIF++ irradiation facility.

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.

Analysis of discharge events in the CMS GE1/1 GEMdetectors in presence of LHC beam

In July 2022, the experiments installed on the Large Hadron Collider (LHC) accelerator ring started a new data taking phase, Run-3. Before this period, an upgrade campaign took place during the so called Long Shutdown 2 (2018–2022). In particular, the muon system of the CMS experiment has been upgraded with the installation of a new gas detector station, GE1/1, based on Gas Electron Multiplier technology (GEM). The CMS experiment has scheduled the installation of two additional GEM stations: GE2/1 and ME0. The aim of the GEM stations is to maintain the performance of the muon system, reached during the last data taking phase (Run-2), with the increase of instantaneous luminosity expected at the LHC. The installed GE1/1 station covers the pseudorapidity region 1.55 <|η|< 2.18. GE1/1 participated in the CMS Run-3 data taking from July to November 2022 and, in this period, its detectors were exposed for the first time to the radiation produced during the collisions of the LHC beams, with a center of mass energy of 13.6 TeV. Since the first days of Run-3, where only a few bunches collided in CMS, the GE1/1 detectors started to experience a significant number of discharges, affecting their smooth operation during the data taking. In this talk, we present an analysis of discharges, which started by simply counting the number of discharges occurring per detector. An interesting phenomenon observed was that the discharge rate can vary a lot among the installed detectors; this is due to the fact that the occurrence of discharges is driven by the manufacturing of the GEM foils used in the detectors. Imperfections in their manufacturing can lead to large variation in the discharge rate. In addition, the rate can vary in time, due to the fact that discharges can produce damage at the site generating them, deactivating a particular hole or, in the worst case, producing a short circuit in the GEM foil, deactivating a part of the foil amplification region. We present the evolution of the discharge rate in time and its dependence on the HV working point and on the luminosity delivered by the LHC beams. This contribution illustrates the actions taken to mitigate the discharge rate and to assure a smooth detector operation.

Exploring the potential of muon radiography for blast furnace assessments: advancements in non-invasive imaging and structural analysis

The BLEMAB European project (BLast furnace stack density Estimation through online Muon ABsorption measurements), the evolution of the previous Mu-Blast European project, is designed to investigate in detail the capability of muon radiography techniques applied to the imaging of the inner zone of a blast furnace. In particular, the goal of this collaboration is to characterize the internal region (so-called cohesive zone) where the slowly downward-moving material begins to soften and melt, which plays an important role in the performance of the blast furnace itself. In this contribution, we describe the state-of-the-art of the muon tracking system which is currently being developed and installed at a blast furnace on the ArcelorMittal site in Bremen (Germany). Moreover, we will present the GEANT4 simulation framework devised for this application together with the simulation results. Finally, we will show the possible contribution of multiple scattering effects to such peculiar applications.

The CMS Muon System and Features of Its Operation with HL-LHC

The CMS Muon System and Features of Its Operation with HL-LHC

Improved resistive plate chambers for HL-LHC upgrade of CMS

In view of the High Luminosity LHC, the CMS Muon system will be upgraded to sustain its efficient muon triggering and reconstruction performance. Resistive Plate Chambers (RPC) are dedicated detectors for muon triggering due to their excellent timing resolution. The RPC system will be extended up to 2.4 in pseudorapidity. Before the LHC Long Shutdown 3, new RE3/1 and RE4/1 stations of the forward Muon system will be equipped with improved Resistive Plate Chambers (iRPC) having, compared to the present RPC system, a different design and geometry and 2D strip readout. This advanced iRPC geometry configuration allows the rate capability to improve and hence survive the harsh background conditions during the HL-LHC phase. Several iRPC demonstrator chambers were installed in CMS during the recently completed 2nd Long Shutdown to study the detector behaviour under real LHC conditions. This paper summarizes the iRPC project and its schedule, including the status of the iRPC production sites, details of the chamber quality control procedures and results of the commissioning of the demonstrator chambers.

Novel silicon detectors in ALICE at the LHC: The ITS3 and ALICE 3 upgrades

The ALICE experiment is preparing for the ITS3 upgrade, which is set to take place during the LHC Long Shutdown 3. The aim of this upgrade is to replace the three innermost tracking layers with truly cylindrical wafer-scale Monolithic Active Pixel Sensors (MAPS). By adopting this innovative technology, ALICE will further reduce the material budget and the distance from the interaction point, thus significantly improving its tracking and vertexing capabilities. The R&amp;D program for ITS3 includes several advancements, such as operability of bent MAPS, validation of the 65 nm CMOS technology, and employment of the stitching process to produce wafer-scale sensors. In addition to the ITS3 upgrade, ALICE is designing a completely new apparatus, ALICE 3, planned for LHC Runs 5 and 6. The detector consists of a large MAPS-based tracking system covering eight units of pseudorapidity, complemented by multiple systems for particle identification, including silicon time-of-flight layers, a ring-imaging Cherenkov detector, a muon identification system, and an electromagnetic calorimeter. The vertex detector is based on an evolution of the ITS3 concept aiming at a track pointing resolution of better than 10 μm for tranverse momenta above 200 MeV/c through the integration of the tracking layers in a retractable structure inside the beam pipe. In this proceeding the detector concept of these upgrades is described, together with their physics motivations and R&amp;D status and achievements.

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.